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1 | =head1 NAME |
2 | |
3 | perlfunc - Perl builtin functions |
4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | The functions in this section can serve as terms in an expression. |
8 | They fall into two major categories: list operators and named unary |
9 | operators. These differ in their precedence relationship with a |
10 | following comma. (See the precedence table in L<perlop>.) List |
11 | operators take more than one argument, while unary operators can never |
12 | take more than one argument. Thus, a comma terminates the argument of |
13 | a unary operator, but merely separates the arguments of a list |
14 | operator. A unary operator generally provides a scalar context to its |
15 | argument, while a list operator may provide either scalar and list |
16 | contexts for its arguments. If it does both, the scalar arguments will |
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17 | be first, and the list argument will follow. (Note that there can ever |
18 | be only one list argument.) For instance, splice() has three scalar |
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19 | arguments followed by a list. |
20 | |
21 | In the syntax descriptions that follow, list operators that expect a |
22 | list (and provide list context for the elements of the list) are shown |
23 | with LIST as an argument. Such a list may consist of any combination |
24 | of scalar arguments or list values; the list values will be included |
25 | in the list as if each individual element were interpolated at that |
26 | point in the list, forming a longer single-dimensional list value. |
27 | Elements of the LIST should be separated by commas. |
28 | |
29 | Any function in the list below may be used either with or without |
30 | parentheses around its arguments. (The syntax descriptions omit the |
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31 | parentheses.) If you use the parentheses, the simple (but occasionally |
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32 | surprising) rule is this: It I<LOOKS> like a function, therefore it I<IS> a |
33 | function, and precedence doesn't matter. Otherwise it's a list |
34 | operator or unary operator, and precedence does matter. And whitespace |
35 | between the function and left parenthesis doesn't count--so you need to |
36 | be careful sometimes: |
37 | |
38 | print 1+2+3; # Prints 6. |
39 | print(1+2) + 3; # Prints 3. |
40 | print (1+2)+3; # Also prints 3! |
41 | print +(1+2)+3; # Prints 6. |
42 | print ((1+2)+3); # Prints 6. |
43 | |
44 | If you run Perl with the B<-w> switch it can warn you about this. For |
45 | example, the third line above produces: |
46 | |
47 | print (...) interpreted as function at - line 1. |
48 | Useless use of integer addition in void context at - line 1. |
49 | |
50 | For functions that can be used in either a scalar or list context, |
51 | non-abortive failure is generally indicated in a scalar context by |
52 | returning the undefined value, and in a list context by returning the |
53 | null list. |
54 | |
55 | Remember the following rule: |
56 | |
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57 | =over 8 |
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58 | |
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59 | =item I<THERE IS NO GENERAL RULE FOR CONVERTING A LIST INTO A SCALAR!> |
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60 | |
61 | =back |
62 | |
63 | Each operator and function decides which sort of value it would be most |
64 | appropriate to return in a scalar context. Some operators return the |
65 | length of the list that would have been returned in a list context. Some |
66 | operators return the first value in the list. Some operators return the |
67 | last value in the list. Some operators return a count of successful |
68 | operations. In general, they do what you want, unless you want |
69 | consistency. |
70 | |
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71 | =head2 Perl Functions by Category |
72 | |
73 | Here are Perl's functions (including things that look like |
74 | functions, like some of the keywords and named operators) |
75 | arranged by category. Some functions appear in more |
76 | than one place. |
77 | |
78 | =over |
79 | |
80 | =item Functions for SCALARs or strings |
81 | |
82 | chomp, chop, chr, crypt, hex, index, lc, lcfirst, length, |
83 | oct, ord, pack, q/STRING/, qq/STRING/, reverse, rindex, |
84 | sprintf, substr, tr///, uc, ucfirst, y/// |
85 | |
86 | =item Regular expressions and pattern matching |
87 | |
88 | m//, pos, quotemeta, s///, split, study |
89 | |
90 | =item Numeric functions |
91 | |
92 | abs, atan2, cos, exp, hex, int, log, oct, rand, sin, sqrt, |
93 | srand |
94 | |
95 | =item Functions for real @ARRAYs |
96 | |
97 | pop, push, shift, splice, unshift |
98 | |
99 | =item Functions for list data |
100 | |
101 | grep, join, map, qw/STRING/, reverse, sort, unpack |
102 | |
103 | =item Functions for real %HASHes |
104 | |
105 | delete, each, exists, keys, values |
106 | |
107 | =item Input and output functions |
108 | |
109 | binmode, close, closedir, dbmclose, dbmopen, die, eof, |
110 | fileno, flock, format, getc, print, printf, read, readdir, |
111 | rewinddir, seek, seekdir, select, syscall, sysread, |
112 | syswrite, tell, telldir, truncate, warn, write |
113 | |
114 | =item Functions for fixed length data or records |
115 | |
116 | pack, read, syscall, sysread, syswrite, unpack, vec |
117 | |
118 | =item Functions for filehandles, files, or directories |
119 | |
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120 | I<-X>, chdir, chmod, chown, chroot, fcntl, glob, ioctl, link, |
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121 | lstat, mkdir, open, opendir, readlink, rename, rmdir, |
122 | stat, symlink, umask, unlink, utime |
123 | |
124 | =item Keywords related to the control flow of your perl program |
125 | |
126 | caller, continue, die, do, dump, eval, exit, goto, last, |
127 | next, redo, return, sub, wantarray |
128 | |
129 | =item Keywords related to scoping |
130 | |
131 | caller, import, local, my, package, use |
132 | |
133 | =item Miscellaneous functions |
134 | |
135 | defined, dump, eval, formline, local, my, reset, scalar, |
136 | undef, wantarray |
137 | |
138 | =item Functions for processes and process groups |
139 | |
140 | alarm, exec, fork, getpgrp, getppid, getpriority, kill, |
141 | pipe, qx/STRING/, setpgrp, setpriority, sleep, system, |
142 | times, wait, waitpid |
143 | |
144 | =item Keywords related to perl modules |
145 | |
146 | do, import, no, package, require, use |
147 | |
148 | =item Keywords related to classes and object-orientedness |
149 | |
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150 | bless, dbmclose, dbmopen, package, ref, tie, tied, untie, use |
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151 | |
152 | =item Low-level socket functions |
153 | |
154 | accept, bind, connect, getpeername, getsockname, |
155 | getsockopt, listen, recv, send, setsockopt, shutdown, |
156 | socket, socketpair |
157 | |
158 | =item System V interprocess communication functions |
159 | |
160 | msgctl, msgget, msgrcv, msgsnd, semctl, semget, semop, |
161 | shmctl, shmget, shmread, shmwrite |
162 | |
163 | =item Fetching user and group info |
164 | |
165 | endgrent, endhostent, endnetent, endpwent, getgrent, |
166 | getgrgid, getgrnam, getlogin, getpwent, getpwnam, |
167 | getpwuid, setgrent, setpwent |
168 | |
169 | =item Fetching network info |
170 | |
171 | endprotoent, endservent, gethostbyaddr, gethostbyname, |
172 | gethostent, getnetbyaddr, getnetbyname, getnetent, |
173 | getprotobyname, getprotobynumber, getprotoent, |
174 | getservbyname, getservbyport, getservent, sethostent, |
175 | setnetent, setprotoent, setservent |
176 | |
177 | =item Time-related functions |
178 | |
179 | gmtime, localtime, time, times |
180 | |
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181 | =item Functions new in perl5 |
182 | |
183 | abs, bless, chomp, chr, exists, formline, glob, import, lc, |
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184 | lcfirst, map, my, no, prototype, qx, qw, readline, readpipe, |
185 | ref, sub*, sysopen, tie, tied, uc, ucfirst, untie, use |
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186 | |
187 | * - C<sub> was a keyword in perl4, but in perl5 it is an |
188 | operator which can be used in expressions. |
189 | |
190 | =item Functions obsoleted in perl5 |
191 | |
192 | dbmclose, dbmopen |
193 | |
194 | |
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195 | =back |
196 | |
197 | =head2 Alphabetical Listing of Perl Functions |
198 | |
199 | |
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200 | =over 8 |
201 | |
202 | =item -X FILEHANDLE |
203 | |
204 | =item -X EXPR |
205 | |
206 | =item -X |
207 | |
208 | A file test, where X is one of the letters listed below. This unary |
209 | operator takes one argument, either a filename or a filehandle, and |
210 | tests the associated file to see if something is true about it. If the |
211 | argument is omitted, tests $_, except for C<-t>, which tests STDIN. |
212 | Unless otherwise documented, it returns C<1> for TRUE and C<''> for FALSE, or |
213 | the undefined value if the file doesn't exist. Despite the funny |
214 | names, precedence is the same as any other named unary operator, and |
215 | the argument may be parenthesized like any other unary operator. The |
216 | operator may be any of: |
217 | |
218 | -r File is readable by effective uid/gid. |
219 | -w File is writable by effective uid/gid. |
220 | -x File is executable by effective uid/gid. |
221 | -o File is owned by effective uid. |
222 | |
223 | -R File is readable by real uid/gid. |
224 | -W File is writable by real uid/gid. |
225 | -X File is executable by real uid/gid. |
226 | -O File is owned by real uid. |
227 | |
228 | -e File exists. |
229 | -z File has zero size. |
230 | -s File has non-zero size (returns size). |
231 | |
232 | -f File is a plain file. |
233 | -d File is a directory. |
234 | -l File is a symbolic link. |
235 | -p File is a named pipe (FIFO). |
236 | -S File is a socket. |
237 | -b File is a block special file. |
238 | -c File is a character special file. |
239 | -t Filehandle is opened to a tty. |
240 | |
241 | -u File has setuid bit set. |
242 | -g File has setgid bit set. |
243 | -k File has sticky bit set. |
244 | |
245 | -T File is a text file. |
246 | -B File is a binary file (opposite of -T). |
247 | |
248 | -M Age of file in days when script started. |
249 | -A Same for access time. |
250 | -C Same for inode change time. |
251 | |
252 | The interpretation of the file permission operators C<-r>, C<-R>, C<-w>, |
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253 | C<-W>, C<-x>, and C<-X> is based solely on the mode of the file and the |
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254 | uids and gids of the user. There may be other reasons you can't actually |
255 | read, write or execute the file. Also note that, for the superuser, |
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256 | C<-r>, C<-R>, C<-w>, and C<-W> always return 1, and C<-x> and C<-X> return |
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257 | 1 if any execute bit is set in the mode. Scripts run by the superuser may |
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258 | thus need to do a stat() to determine the actual mode of the |
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259 | file, or temporarily set the uid to something else. |
260 | |
261 | Example: |
262 | |
263 | while (<>) { |
264 | chop; |
265 | next unless -f $_; # ignore specials |
266 | ... |
267 | } |
268 | |
269 | Note that C<-s/a/b/> does not do a negated substitution. Saying |
270 | C<-exp($foo)> still works as expected, however--only single letters |
271 | following a minus are interpreted as file tests. |
272 | |
273 | The C<-T> and C<-B> switches work as follows. The first block or so of the |
274 | file is examined for odd characters such as strange control codes or |
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275 | characters with the high bit set. If too many odd characters (E<gt>30%) |
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276 | are found, it's a C<-B> file, otherwise it's a C<-T> file. Also, any file |
277 | containing null in the first block is considered a binary file. If C<-T> |
278 | or C<-B> is used on a filehandle, the current stdio buffer is examined |
279 | rather than the first block. Both C<-T> and C<-B> return TRUE on a null |
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280 | file, or a file at EOF when testing a filehandle. Because you have to |
281 | read a file to do the C<-T> test, on most occasions you want to use a C<-f> |
282 | against the file first, as in C<next unless -f $file && -T $file>. |
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283 | |
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284 | If any of the file tests (or either the stat() or lstat() operators) are given |
285 | the special filehandle consisting of a solitary underline, then the stat |
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286 | structure of the previous file test (or stat operator) is used, saving |
287 | a system call. (This doesn't work with C<-t>, and you need to remember |
288 | that lstat() and C<-l> will leave values in the stat structure for the |
289 | symbolic link, not the real file.) Example: |
290 | |
291 | print "Can do.\n" if -r $a || -w _ || -x _; |
292 | |
293 | stat($filename); |
294 | print "Readable\n" if -r _; |
295 | print "Writable\n" if -w _; |
296 | print "Executable\n" if -x _; |
297 | print "Setuid\n" if -u _; |
298 | print "Setgid\n" if -g _; |
299 | print "Sticky\n" if -k _; |
300 | print "Text\n" if -T _; |
301 | print "Binary\n" if -B _; |
302 | |
303 | =item abs VALUE |
304 | |
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305 | =item abs |
306 | |
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307 | Returns the absolute value of its argument. |
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308 | If VALUE is omitted, uses $_. |
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309 | |
310 | =item accept NEWSOCKET,GENERICSOCKET |
311 | |
312 | Accepts an incoming socket connect, just as the accept(2) system call |
313 | does. Returns the packed address if it succeeded, FALSE otherwise. |
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314 | See example in L<perlipc/"Sockets: Client/Server Communication">. |
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315 | |
316 | =item alarm SECONDS |
317 | |
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318 | =item alarm |
319 | |
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320 | Arranges to have a SIGALRM delivered to this process after the |
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321 | specified number of seconds have elapsed. If SECONDS is not specified, |
322 | the value stored in $_ is used. (On some machines, |
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323 | unfortunately, the elapsed time may be up to one second less than you |
324 | specified because of how seconds are counted.) Only one timer may be |
325 | counting at once. Each call disables the previous timer, and an |
326 | argument of 0 may be supplied to cancel the previous timer without |
327 | starting a new one. The returned value is the amount of time remaining |
328 | on the previous timer. |
329 | |
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330 | For delays of finer granularity than one second, you may use Perl's |
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331 | syscall() interface to access setitimer(2) if your system supports it, |
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332 | or else see L</select()> below. It is not advised to intermix alarm() |
333 | and sleep() calls. |
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334 | |
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335 | If you want to use alarm() to time out a system call you need to use an |
336 | eval/die pair. You can't rely on the alarm causing the system call to |
337 | fail with $! set to EINTR because Perl sets up signal handlers to |
338 | restart system calls on some systems. Using eval/die always works. |
339 | |
340 | eval { |
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341 | local $SIG{ALRM} = sub { die "alarm\n" }; # NB \n required |
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342 | alarm $timeout; |
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343 | $nread = sysread SOCKET, $buffer, $size; |
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344 | alarm 0; |
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345 | }; |
346 | die if $@ && $@ ne "alarm\n"; # propagate errors |
347 | if ($@) { |
348 | # timed out |
349 | } |
350 | else { |
351 | # didn't |
352 | } |
353 | |
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354 | =item atan2 Y,X |
355 | |
356 | Returns the arctangent of Y/X in the range -PI to PI. |
357 | |
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358 | For the tangent operation, you may use the POSIX::tan() |
359 | function, or use the familiar relation: |
360 | |
361 | sub tan { sin($_[0]) / cos($_[0]) } |
362 | |
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363 | =item bind SOCKET,NAME |
364 | |
365 | Binds a network address to a socket, just as the bind system call |
366 | does. Returns TRUE if it succeeded, FALSE otherwise. NAME should be a |
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367 | packed address of the appropriate type for the socket. See the examples in |
368 | L<perlipc/"Sockets: Client/Server Communication">. |
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369 | |
370 | =item binmode FILEHANDLE |
371 | |
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372 | Arranges for the file to be read or written in "binary" mode in operating |
373 | systems that distinguish between binary and text files. Files that are |
374 | not in binary mode have CR LF sequences translated to LF on input and LF |
375 | translated to CR LF on output. Binmode has no effect under Unix; in DOS |
376 | and similarly archaic systems, it may be imperative--otherwise your |
377 | DOS-damaged C library may mangle your file. The key distinction between |
378 | systems that need binmode and those that don't is their text file |
379 | formats. Systems like Unix and Plan9 that delimit lines with a single |
380 | character, and that encode that character in C as '\n', do not need |
381 | C<binmode>. The rest need it. If FILEHANDLE is an expression, the value |
382 | is taken as the name of the filehandle. |
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383 | |
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384 | =item bless REF,CLASSNAME |
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385 | |
386 | =item bless REF |
387 | |
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388 | This function tells the thingy referenced by REF that it is now |
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389 | an object in the CLASSNAME package--or the current package if no CLASSNAME |
390 | is specified, which is often the case. It returns the reference for |
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391 | convenience, because a bless() is often the last thing in a constructor. |
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392 | Always use the two-argument version if the function doing the blessing |
393 | might be inherited by a derived class. See L<perlobj> for more about the |
394 | blessing (and blessings) of objects. |
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395 | |
396 | =item caller EXPR |
397 | |
398 | =item caller |
399 | |
400 | Returns the context of the current subroutine call. In a scalar context, |
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401 | returns the caller's package name if there is a caller, that is, if |
402 | we're in a subroutine or eval() or require(), and the undefined value |
403 | otherwise. In a list context, returns |
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404 | |
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405 | ($package, $filename, $line) = caller; |
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406 | |
407 | With EXPR, it returns some extra information that the debugger uses to |
408 | print a stack trace. The value of EXPR indicates how many call frames |
409 | to go back before the current one. |
410 | |
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411 | ($package, $filename, $line, $subroutine, |
412 | $hasargs, $wantarray, $evaltext, $is_require) = caller($i); |
413 | |
414 | Here $subroutine may be C<"(eval)"> if the frame is not a subroutine |
415 | call, but C<L<eval>>. In such a case additional elements $evaltext and |
416 | $is_require are set: $is_require is true if the frame is created by |
417 | C<L<require>> or C<L<use>> statement, $evaltext contains the text of |
418 | C<L<eval EXPR>> statement. In particular, for C<L<eval BLOCK>> |
419 | statement $filename is C<"(eval)">, but $evaltext is undefined. (Note |
420 | also that C<L<use>> statement creates a C<L<require>> frame inside |
421 | an C<L<eval EXPR>>) frame. |
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422 | |
423 | Furthermore, when called from within the DB package, caller returns more |
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424 | detailed information: it sets the list variable @DB::args to be the |
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425 | arguments with which that subroutine was invoked. |
426 | |
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427 | =item chdir EXPR |
428 | |
429 | Changes the working directory to EXPR, if possible. If EXPR is |
430 | omitted, changes to home directory. Returns TRUE upon success, FALSE |
431 | otherwise. See example under die(). |
432 | |
433 | =item chmod LIST |
434 | |
435 | Changes the permissions of a list of files. The first element of the |
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436 | list must be the numerical mode, which should probably be an octal |
437 | number. Returns the number of files successfully changed. |
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438 | |
439 | $cnt = chmod 0755, 'foo', 'bar'; |
440 | chmod 0755, @executables; |
441 | |
442 | =item chomp VARIABLE |
443 | |
444 | =item chomp LIST |
445 | |
446 | =item chomp |
447 | |
448 | This is a slightly safer version of chop (see below). It removes any |
449 | line ending that corresponds to the current value of C<$/> (also known as |
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450 | $INPUT_RECORD_SEPARATOR in the C<English> module). It returns the total |
451 | number of characters removed from all its arguments. It's often used to |
452 | remove the newline from the end of an input record when you're worried |
453 | that the final record may be missing its newline. When in paragraph mode |
454 | (C<$/ = "">), it removes all trailing newlines from the string. If |
455 | VARIABLE is omitted, it chomps $_. Example: |
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456 | |
457 | while (<>) { |
458 | chomp; # avoid \n on last field |
459 | @array = split(/:/); |
460 | ... |
461 | } |
462 | |
463 | You can actually chomp anything that's an lvalue, including an assignment: |
464 | |
465 | chomp($cwd = `pwd`); |
466 | chomp($answer = <STDIN>); |
467 | |
468 | If you chomp a list, each element is chomped, and the total number of |
469 | characters removed is returned. |
470 | |
471 | =item chop VARIABLE |
472 | |
473 | =item chop LIST |
474 | |
475 | =item chop |
476 | |
477 | Chops off the last character of a string and returns the character |
478 | chopped. It's used primarily to remove the newline from the end of an |
479 | input record, but is much more efficient than C<s/\n//> because it neither |
480 | scans nor copies the string. If VARIABLE is omitted, chops $_. |
481 | Example: |
482 | |
483 | while (<>) { |
484 | chop; # avoid \n on last field |
485 | @array = split(/:/); |
486 | ... |
487 | } |
488 | |
489 | You can actually chop anything that's an lvalue, including an assignment: |
490 | |
491 | chop($cwd = `pwd`); |
492 | chop($answer = <STDIN>); |
493 | |
494 | If you chop a list, each element is chopped. Only the value of the |
495 | last chop is returned. |
496 | |
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497 | Note that chop returns the last character. To return all but the last |
498 | character, use C<substr($string, 0, -1)>. |
499 | |
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500 | =item chown LIST |
501 | |
502 | Changes the owner (and group) of a list of files. The first two |
503 | elements of the list must be the I<NUMERICAL> uid and gid, in that order. |
504 | Returns the number of files successfully changed. |
505 | |
506 | $cnt = chown $uid, $gid, 'foo', 'bar'; |
507 | chown $uid, $gid, @filenames; |
508 | |
509 | Here's an example that looks up non-numeric uids in the passwd file: |
510 | |
511 | print "User: "; |
512 | chop($user = <STDIN>); |
513 | print "Files: " |
514 | chop($pattern = <STDIN>); |
515 | |
516 | ($login,$pass,$uid,$gid) = getpwnam($user) |
517 | or die "$user not in passwd file"; |
518 | |
519 | @ary = <${pattern}>; # expand filenames |
520 | chown $uid, $gid, @ary; |
521 | |
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522 | On most systems, you are not allowed to change the ownership of the |
523 | file unless you're the superuser, although you should be able to change |
524 | the group to any of your secondary groups. On insecure systems, these |
525 | restrictions may be relaxed, but this is not a portable assumption. |
526 | |
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527 | =item chr NUMBER |
528 | |
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529 | =item chr |
530 | |
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531 | Returns the character represented by that NUMBER in the character set. |
532 | For example, C<chr(65)> is "A" in ASCII. |
533 | |
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534 | If NUMBER is omitted, uses $_. |
535 | |
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536 | =item chroot FILENAME |
537 | |
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538 | =item chroot |
539 | |
4633a7c4 |
540 | This function works as the system call by the same name: it makes the |
541 | named directory the new root directory for all further pathnames that |
542 | begin with a "/" by your process and all of its children. (It doesn't |
28757baa |
543 | change your current working directory, which is unaffected.) For security |
4633a7c4 |
544 | reasons, this call is restricted to the superuser. If FILENAME is |
545 | omitted, does chroot to $_. |
a0d0e21e |
546 | |
547 | =item close FILEHANDLE |
548 | |
549 | Closes the file or pipe associated with the file handle, returning TRUE |
550 | only if stdio successfully flushes buffers and closes the system file |
551 | descriptor. You don't have to close FILEHANDLE if you are immediately |
5f05dabc |
552 | going to do another open() on it, because open() will close it for you. (See |
a0d0e21e |
553 | open().) However, an explicit close on an input file resets the line |
554 | counter ($.), while the implicit close done by open() does not. Also, |
555 | closing a pipe will wait for the process executing on the pipe to |
556 | complete, in case you want to look at the output of the pipe |
557 | afterwards. Closing a pipe explicitly also puts the status value of |
558 | the command into C<$?>. Example: |
559 | |
560 | open(OUTPUT, '|sort >foo'); # pipe to sort |
561 | ... # print stuff to output |
562 | close OUTPUT; # wait for sort to finish |
563 | open(INPUT, 'foo'); # get sort's results |
564 | |
565 | FILEHANDLE may be an expression whose value gives the real filehandle name. |
566 | |
567 | =item closedir DIRHANDLE |
568 | |
569 | Closes a directory opened by opendir(). |
570 | |
571 | =item connect SOCKET,NAME |
572 | |
573 | Attempts to connect to a remote socket, just as the connect system call |
574 | does. Returns TRUE if it succeeded, FALSE otherwise. NAME should be a |
4633a7c4 |
575 | packed address of the appropriate type for the socket. See the examples in |
576 | L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e |
577 | |
cb1a09d0 |
578 | =item continue BLOCK |
579 | |
580 | Actually a flow control statement rather than a function. If there is a |
581 | C<continue> BLOCK attached to a BLOCK (typically in a C<while> or |
582 | C<foreach>), it is always executed just before the conditional is about to |
583 | be evaluated again, just like the third part of a C<for> loop in C. Thus |
584 | it can be used to increment a loop variable, even when the loop has been |
585 | continued via the C<next> statement (which is similar to the C C<continue> |
586 | statement). |
587 | |
a0d0e21e |
588 | =item cos EXPR |
589 | |
590 | Returns the cosine of EXPR (expressed in radians). If EXPR is omitted |
591 | takes cosine of $_. |
592 | |
28757baa |
593 | For the inverse cosine operation, you may use the POSIX::acos() |
594 | function, or use this relation: |
595 | |
596 | sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) } |
597 | |
a0d0e21e |
598 | =item crypt PLAINTEXT,SALT |
599 | |
4633a7c4 |
600 | Encrypts a string exactly like the crypt(3) function in the C library |
601 | (assuming that you actually have a version there that has not been |
602 | extirpated as a potential munition). This can prove useful for checking |
603 | the password file for lousy passwords, amongst other things. Only the |
604 | guys wearing white hats should do this. |
a0d0e21e |
605 | |
606 | Here's an example that makes sure that whoever runs this program knows |
607 | their own password: |
608 | |
609 | $pwd = (getpwuid($<))[1]; |
610 | $salt = substr($pwd, 0, 2); |
611 | |
612 | system "stty -echo"; |
613 | print "Password: "; |
614 | chop($word = <STDIN>); |
615 | print "\n"; |
616 | system "stty echo"; |
617 | |
618 | if (crypt($word, $salt) ne $pwd) { |
619 | die "Sorry...\n"; |
620 | } else { |
621 | print "ok\n"; |
622 | } |
623 | |
5f05dabc |
624 | Of course, typing in your own password to whomever asks you |
748a9306 |
625 | for it is unwise. |
a0d0e21e |
626 | |
627 | =item dbmclose ASSOC_ARRAY |
628 | |
629 | [This function has been superseded by the untie() function.] |
630 | |
631 | Breaks the binding between a DBM file and an associative array. |
632 | |
633 | =item dbmopen ASSOC,DBNAME,MODE |
634 | |
635 | [This function has been superseded by the tie() function.] |
636 | |
cb1a09d0 |
637 | This binds a dbm(3), ndbm(3), sdbm(3), gdbm(), or Berkeley DB file to an |
638 | associative array. ASSOC is the name of the associative array. (Unlike |
639 | normal open, the first argument is I<NOT> a filehandle, even though it |
640 | looks like one). DBNAME is the name of the database (without the F<.dir> |
641 | or F<.pag> extension if any). If the database does not exist, it is |
642 | created with protection specified by MODE (as modified by the umask()). |
5f05dabc |
643 | If your system supports only the older DBM functions, you may perform only |
cb1a09d0 |
644 | one dbmopen() in your program. In older versions of Perl, if your system |
645 | had neither DBM nor ndbm, calling dbmopen() produced a fatal error; it now |
646 | falls back to sdbm(3). |
a0d0e21e |
647 | |
648 | If you don't have write access to the DBM file, you can only read |
649 | associative array variables, not set them. If you want to test whether |
650 | you can write, either use file tests or try setting a dummy array entry |
651 | inside an eval(), which will trap the error. |
652 | |
653 | Note that functions such as keys() and values() may return huge array |
654 | values when used on large DBM files. You may prefer to use the each() |
655 | function to iterate over large DBM files. Example: |
656 | |
657 | # print out history file offsets |
658 | dbmopen(%HIST,'/usr/lib/news/history',0666); |
659 | while (($key,$val) = each %HIST) { |
660 | print $key, ' = ', unpack('L',$val), "\n"; |
661 | } |
662 | dbmclose(%HIST); |
663 | |
cb1a09d0 |
664 | See also L<AnyDBM_File> for a more general description of the pros and |
184e9718 |
665 | cons of the various dbm approaches, as well as L<DB_File> for a particularly |
cb1a09d0 |
666 | rich implementation. |
4633a7c4 |
667 | |
a0d0e21e |
668 | =item defined EXPR |
669 | |
bbce6d69 |
670 | =item defined |
671 | |
cb1a09d0 |
672 | Returns a boolean value saying whether EXPR has a real value |
bbce6d69 |
673 | or not. If EXPR is not present, $_ will be checked. Many operations |
674 | return the undefined value under exceptional conditions, such as end of |
675 | file, uninitialized variable, system error and such. This function |
676 | allows you to distinguish between an undefined |
a0d0e21e |
677 | null scalar and a defined null scalar with operations that might return |
678 | a real null string, such as referencing elements of an array. You may |
679 | also check to see if arrays or subroutines exist. Use of defined on |
680 | predefined variables is not guaranteed to produce intuitive results. |
681 | |
682 | When used on a hash array element, it tells you whether the value |
683 | is defined, not whether the key exists in the hash. Use exists() for that. |
684 | |
685 | Examples: |
686 | |
687 | print if defined $switch{'D'}; |
688 | print "$val\n" while defined($val = pop(@ary)); |
689 | die "Can't readlink $sym: $!" |
690 | unless defined($value = readlink $sym); |
691 | eval '@foo = ()' if defined(@foo); |
692 | die "No XYZ package defined" unless defined %_XYZ; |
693 | sub foo { defined &$bar ? &$bar(@_) : die "No bar"; } |
694 | |
695 | See also undef(). |
696 | |
a5f75d66 |
697 | Note: many folks tend to overuse defined(), and then are surprised to |
698 | discover that the number 0 and the null string are, in fact, defined |
699 | concepts. For example, if you say |
700 | |
701 | "ab" =~ /a(.*)b/; |
702 | |
703 | the pattern match succeeds, and $1 is defined, despite the fact that it |
704 | matched "nothing". But it didn't really match nothing--rather, it |
705 | matched something that happened to be 0 characters long. This is all |
706 | very above-board and honest. When a function returns an undefined value, |
707 | it's an admission that it couldn't give you an honest answer. So |
5f05dabc |
708 | you should use defined() only when you're questioning the integrity |
a5f75d66 |
709 | of what you're trying to do. At other times, a simple comparison to |
710 | 0 or "" is what you want. |
711 | |
28757baa |
712 | Another surprise is that using defined() on an entire array or |
713 | hash reports whether memory for that aggregate has ever been |
714 | allocated. So an array you set to the empty list appears undefined |
715 | initially, and one that once was full and that you then set to |
716 | the empty list still appears defined. You should instead use a |
717 | simple test for size: |
718 | |
719 | if (@an_array) { print "has array elements\n" } |
720 | if (%a_hash) { print "has hash members\n" } |
721 | |
722 | Using undef() on these, however, does clear their memory and then report |
723 | them as not defined anymore, but you shoudln't do that unless you don't |
724 | plan to use them again, because it saves time when you load them up |
725 | again to have memory already ready to be filled. |
726 | |
727 | This counter-intuitive behaviour of defined() on aggregates may be |
728 | changed, fixed, or broken in a future release of Perl. |
729 | |
a0d0e21e |
730 | =item delete EXPR |
731 | |
5f05dabc |
732 | Deletes the specified key(s) and their associated values from a hash |
733 | array. For each key, returns the deleted value associated with that key, |
734 | or the undefined value if there was no such key. Deleting from C<$ENV{}> |
735 | modifies the environment. Deleting from an array tied to a DBM file |
736 | deletes the entry from the DBM file. (But deleting from a tie()d hash |
737 | doesn't necessarily return anything.) |
a0d0e21e |
738 | |
739 | The following deletes all the values of an associative array: |
740 | |
5f05dabc |
741 | foreach $key (keys %HASH) { |
742 | delete $HASH{$key}; |
a0d0e21e |
743 | } |
744 | |
5f05dabc |
745 | And so does this: |
746 | |
747 | delete @HASH{keys %HASH} |
748 | |
749 | (But both of these are slower than the undef() command.) Note that the |
750 | EXPR can be arbitrarily complicated as long as the final operation is a |
751 | hash element lookup or hash slice: |
a0d0e21e |
752 | |
753 | delete $ref->[$x][$y]{$key}; |
5f05dabc |
754 | delete @{$ref->[$x][$y]}{$key1, $key2, @morekeys}; |
a0d0e21e |
755 | |
756 | =item die LIST |
757 | |
758 | Outside of an eval(), prints the value of LIST to C<STDERR> and exits with |
184e9718 |
759 | the current value of C<$!> (errno). If C<$!> is 0, exits with the value of |
28757baa |
760 | C<($? E<gt>E<gt> 8)> (back-tick `command` status). If C<($? E<gt>E<gt> 8)> |
761 | is 0, exits with 255. Inside an eval(), the error message is stuffed into |
762 | C<$@>, and the eval() is terminated with the undefined value; this makes |
763 | die() the way to raise an exception. |
a0d0e21e |
764 | |
765 | Equivalent examples: |
766 | |
767 | die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news'; |
768 | chdir '/usr/spool/news' or die "Can't cd to spool: $!\n" |
769 | |
770 | If the value of EXPR does not end in a newline, the current script line |
771 | number and input line number (if any) are also printed, and a newline |
772 | is supplied. Hint: sometimes appending ", stopped" to your message |
773 | will cause it to make better sense when the string "at foo line 123" is |
774 | appended. Suppose you are running script "canasta". |
775 | |
776 | die "/etc/games is no good"; |
777 | die "/etc/games is no good, stopped"; |
778 | |
779 | produce, respectively |
780 | |
781 | /etc/games is no good at canasta line 123. |
782 | /etc/games is no good, stopped at canasta line 123. |
783 | |
784 | See also exit() and warn(). |
785 | |
786 | =item do BLOCK |
787 | |
788 | Not really a function. Returns the value of the last command in the |
789 | sequence of commands indicated by BLOCK. When modified by a loop |
790 | modifier, executes the BLOCK once before testing the loop condition. |
791 | (On other statements the loop modifiers test the conditional first.) |
792 | |
793 | =item do SUBROUTINE(LIST) |
794 | |
795 | A deprecated form of subroutine call. See L<perlsub>. |
796 | |
797 | =item do EXPR |
798 | |
799 | Uses the value of EXPR as a filename and executes the contents of the |
800 | file as a Perl script. Its primary use is to include subroutines |
801 | from a Perl subroutine library. |
802 | |
803 | do 'stat.pl'; |
804 | |
805 | is just like |
806 | |
807 | eval `cat stat.pl`; |
808 | |
809 | except that it's more efficient, more concise, keeps track of the |
810 | current filename for error messages, and searches all the B<-I> |
811 | libraries if the file isn't in the current directory (see also the @INC |
812 | array in L<perlvar/Predefined Names>). It's the same, however, in that it does |
5f05dabc |
813 | re-parse the file every time you call it, so you probably don't want to |
a0d0e21e |
814 | do this inside a loop. |
815 | |
816 | Note that inclusion of library modules is better done with the |
4633a7c4 |
817 | use() and require() operators, which also do error checking |
818 | and raise an exception if there's a problem. |
a0d0e21e |
819 | |
820 | =item dump LABEL |
821 | |
822 | This causes an immediate core dump. Primarily this is so that you can |
823 | use the B<undump> program to turn your core dump into an executable binary |
824 | after having initialized all your variables at the beginning of the |
825 | program. When the new binary is executed it will begin by executing a |
826 | C<goto LABEL> (with all the restrictions that C<goto> suffers). Think of |
827 | it as a goto with an intervening core dump and reincarnation. If LABEL |
828 | is omitted, restarts the program from the top. WARNING: any files |
829 | opened at the time of the dump will NOT be open any more when the |
830 | program is reincarnated, with possible resulting confusion on the part |
831 | of Perl. See also B<-u> option in L<perlrun>. |
832 | |
833 | Example: |
834 | |
835 | #!/usr/bin/perl |
836 | require 'getopt.pl'; |
837 | require 'stat.pl'; |
838 | %days = ( |
839 | 'Sun' => 1, |
840 | 'Mon' => 2, |
841 | 'Tue' => 3, |
842 | 'Wed' => 4, |
843 | 'Thu' => 5, |
844 | 'Fri' => 6, |
845 | 'Sat' => 7, |
846 | ); |
847 | |
848 | dump QUICKSTART if $ARGV[0] eq '-d'; |
849 | |
850 | QUICKSTART: |
851 | Getopt('f'); |
852 | |
853 | =item each ASSOC_ARRAY |
854 | |
da0045b7 |
855 | When called in a list context, returns a 2-element array consisting |
856 | of the key and value for the next element of an associative array, |
857 | so that you can iterate over it. When called in a scalar context, |
5f05dabc |
858 | returns the key for only the next element in the associative array. |
a0d0e21e |
859 | Entries are returned in an apparently random order. When the array is |
da0045b7 |
860 | entirely read, a null array is returned in list context (which when |
861 | assigned produces a FALSE (0) value), and C<undef> is returned in a |
862 | scalar context. The next call to each() after that will start |
a0d0e21e |
863 | iterating again. The iterator can be reset only by reading all the |
864 | elements from the array. You should not add elements to an array while |
865 | you're iterating over it. There is a single iterator for each |
5f05dabc |
866 | associative array, shared by all each(), keys(), and values() function |
a0d0e21e |
867 | calls in the program. The following prints out your environment like |
868 | the printenv(1) program, only in a different order: |
869 | |
870 | while (($key,$value) = each %ENV) { |
871 | print "$key=$value\n"; |
872 | } |
873 | |
874 | See also keys() and values(). |
875 | |
876 | =item eof FILEHANDLE |
877 | |
4633a7c4 |
878 | =item eof () |
879 | |
a0d0e21e |
880 | =item eof |
881 | |
882 | Returns 1 if the next read on FILEHANDLE will return end of file, or if |
883 | FILEHANDLE is not open. FILEHANDLE may be an expression whose value |
884 | gives the real filehandle name. (Note that this function actually |
885 | reads a character and then ungetc()s it, so it is not very useful in an |
748a9306 |
886 | interactive context.) Do not read from a terminal file (or call |
887 | C<eof(FILEHANDLE)> on it) after end-of-file is reached. Filetypes such |
888 | as terminals may lose the end-of-file condition if you do. |
889 | |
890 | An C<eof> without an argument uses the last file read as argument. |
891 | Empty parentheses () may be used to indicate |
5f05dabc |
892 | the pseudo file formed of the files listed on the command line, i.e., |
37798a01 |
893 | C<eof()> is reasonable to use inside a while (E<lt>E<gt>) loop to detect the end |
a0d0e21e |
894 | of only the last file. Use C<eof(ARGV)> or eof without the parentheses to |
37798a01 |
895 | test I<EACH> file in a while (E<lt>E<gt>) loop. Examples: |
a0d0e21e |
896 | |
748a9306 |
897 | # reset line numbering on each input file |
898 | while (<>) { |
899 | print "$.\t$_"; |
900 | close(ARGV) if (eof); # Not eof(). |
901 | } |
902 | |
a0d0e21e |
903 | # insert dashes just before last line of last file |
904 | while (<>) { |
905 | if (eof()) { |
906 | print "--------------\n"; |
748a9306 |
907 | close(ARGV); # close or break; is needed if we |
908 | # are reading from the terminal |
a0d0e21e |
909 | } |
910 | print; |
911 | } |
912 | |
a0d0e21e |
913 | Practical hint: you almost never need to use C<eof> in Perl, because the |
37798a01 |
914 | input operators return undef when they run out of data. |
a0d0e21e |
915 | |
916 | =item eval EXPR |
917 | |
918 | =item eval BLOCK |
919 | |
920 | EXPR is parsed and executed as if it were a little Perl program. It |
921 | is executed in the context of the current Perl program, so that any |
5f05dabc |
922 | variable settings or subroutine and format definitions remain afterwards. |
a0d0e21e |
923 | The value returned is the value of the last expression evaluated, or a |
55497cff |
924 | return statement may be used, just as with subroutines. The last |
925 | expression is evaluated in scalar or array context, depending on the |
926 | context of the eval. |
a0d0e21e |
927 | |
928 | If there is a syntax error or runtime error, or a die() statement is |
929 | executed, an undefined value is returned by eval(), and C<$@> is set to the |
930 | error message. If there was no error, C<$@> is guaranteed to be a null |
931 | string. If EXPR is omitted, evaluates $_. The final semicolon, if |
932 | any, may be omitted from the expression. |
933 | |
5f05dabc |
934 | Note that, because eval() traps otherwise-fatal errors, it is useful for |
4633a7c4 |
935 | determining whether a particular feature (such as socket() or symlink()) |
a0d0e21e |
936 | is implemented. It is also Perl's exception trapping mechanism, where |
937 | the die operator is used to raise exceptions. |
938 | |
939 | If the code to be executed doesn't vary, you may use the eval-BLOCK |
940 | form to trap run-time errors without incurring the penalty of |
941 | recompiling each time. The error, if any, is still returned in C<$@>. |
942 | Examples: |
943 | |
944 | # make divide-by-zero non-fatal |
945 | eval { $answer = $a / $b; }; warn $@ if $@; |
946 | |
947 | # same thing, but less efficient |
948 | eval '$answer = $a / $b'; warn $@ if $@; |
949 | |
950 | # a compile-time error |
951 | eval { $answer = }; |
952 | |
953 | # a run-time error |
954 | eval '$answer ='; # sets $@ |
955 | |
956 | With an eval(), you should be especially careful to remember what's |
957 | being looked at when: |
958 | |
959 | eval $x; # CASE 1 |
960 | eval "$x"; # CASE 2 |
961 | |
962 | eval '$x'; # CASE 3 |
963 | eval { $x }; # CASE 4 |
964 | |
965 | eval "\$$x++" # CASE 5 |
966 | $$x++; # CASE 6 |
967 | |
968 | Cases 1 and 2 above behave identically: they run the code contained in the |
969 | variable $x. (Although case 2 has misleading double quotes making the |
970 | reader wonder what else might be happening (nothing is).) Cases 3 and 4 |
184e9718 |
971 | likewise behave in the same way: they run the code E<lt>$xE<gt>, which does |
a0d0e21e |
972 | nothing at all. (Case 4 is preferred for purely visual reasons.) Case 5 |
973 | is a place where normally you I<WOULD> like to use double quotes, except |
cb1a09d0 |
974 | that in that particular situation, you can just use symbolic references |
a0d0e21e |
975 | instead, as in case 6. |
976 | |
977 | =item exec LIST |
978 | |
55497cff |
979 | The exec() function executes a system command I<AND NEVER RETURNS>, |
980 | unless the command does not exist and is executed directly instead of |
981 | via C</bin/sh -c> (see below). Use system() instead of exec() if you |
982 | want it to return. |
a0d0e21e |
983 | |
984 | If there is more than one argument in LIST, or if LIST is an array with |
985 | more than one value, calls execvp(3) with the arguments in LIST. If |
986 | there is only one scalar argument, the argument is checked for shell |
987 | metacharacters. If there are any, the entire argument is passed to |
988 | C</bin/sh -c> for parsing. If there are none, the argument is split |
989 | into words and passed directly to execvp(), which is more efficient. |
37798a01 |
990 | Note: exec() and system() do not flush your output buffer, so you may |
a0d0e21e |
991 | need to set C<$|> to avoid lost output. Examples: |
992 | |
993 | exec '/bin/echo', 'Your arguments are: ', @ARGV; |
994 | exec "sort $outfile | uniq"; |
995 | |
996 | If you don't really want to execute the first argument, but want to lie |
997 | to the program you are executing about its own name, you can specify |
998 | the program you actually want to run as an "indirect object" (without a |
999 | comma) in front of the LIST. (This always forces interpretation of the |
1000 | LIST as a multi-valued list, even if there is only a single scalar in |
1001 | the list.) Example: |
1002 | |
1003 | $shell = '/bin/csh'; |
1004 | exec $shell '-sh'; # pretend it's a login shell |
1005 | |
1006 | or, more directly, |
1007 | |
1008 | exec {'/bin/csh'} '-sh'; # pretend it's a login shell |
1009 | |
1010 | =item exists EXPR |
1011 | |
1012 | Returns TRUE if the specified hash key exists in its hash array, even |
1013 | if the corresponding value is undefined. |
1014 | |
1015 | print "Exists\n" if exists $array{$key}; |
1016 | print "Defined\n" if defined $array{$key}; |
1017 | print "True\n" if $array{$key}; |
1018 | |
5f05dabc |
1019 | A hash element can be TRUE only if it's defined, and defined if |
a0d0e21e |
1020 | it exists, but the reverse doesn't necessarily hold true. |
1021 | |
1022 | Note that the EXPR can be arbitrarily complicated as long as the final |
1023 | operation is a hash key lookup: |
1024 | |
1025 | if (exists $ref->[$x][$y]{$key}) { ... } |
1026 | |
1027 | =item exit EXPR |
1028 | |
1029 | Evaluates EXPR and exits immediately with that value. (Actually, it |
1030 | calls any defined C<END> routines first, but the C<END> routines may not |
1031 | abort the exit. Likewise any object destructors that need to be called |
1032 | are called before exit.) Example: |
1033 | |
1034 | $ans = <STDIN>; |
1035 | exit 0 if $ans =~ /^[Xx]/; |
1036 | |
1037 | See also die(). If EXPR is omitted, exits with 0 status. |
1038 | |
28757baa |
1039 | You shouldn't use exit() to abort a subroutine if there's any chance that |
1040 | someone might want to trap whatever error happened. Use die() instead, |
1041 | which can be trapped by an eval(). |
1042 | |
a0d0e21e |
1043 | =item exp EXPR |
1044 | |
bbce6d69 |
1045 | =item exp |
1046 | |
a0d0e21e |
1047 | Returns I<e> (the natural logarithm base) to the power of EXPR. |
1048 | If EXPR is omitted, gives C<exp($_)>. |
1049 | |
1050 | =item fcntl FILEHANDLE,FUNCTION,SCALAR |
1051 | |
1052 | Implements the fcntl(2) function. You'll probably have to say |
1053 | |
1054 | use Fcntl; |
1055 | |
1056 | first to get the correct function definitions. Argument processing and |
1057 | value return works just like ioctl() below. Note that fcntl() will produce |
1058 | a fatal error if used on a machine that doesn't implement fcntl(2). |
1059 | For example: |
1060 | |
1061 | use Fcntl; |
1062 | fcntl($filehandle, F_GETLK, $packed_return_buffer); |
1063 | |
1064 | =item fileno FILEHANDLE |
1065 | |
1066 | Returns the file descriptor for a filehandle. This is useful for |
1067 | constructing bitmaps for select(). If FILEHANDLE is an expression, the |
1068 | value is taken as the name of the filehandle. |
1069 | |
1070 | =item flock FILEHANDLE,OPERATION |
1071 | |
8ebc5c01 |
1072 | Calls flock(2), or an emulation of it, on FILEHANDLE. Returns TRUE for |
1073 | success, FALSE on failure. Will produce a fatal error if used on a |
1074 | machine that doesn't implement flock(2), fcntl(2) locking, or lockf(3). |
1075 | flock() is Perl's portable file locking interface, although it will lock |
1076 | only entire files, not records. |
1077 | |
1078 | OPERATION is one of LOCK_SH, LOCK_EX, or LOCK_UN, possibly combined with |
1079 | LOCK_NB. These constants are traditionally valued 1, 2, 8 and 4, but |
1080 | you can use the symbolic names if you pull them in with an explicit |
1081 | request to the Fcntl module. The names can be requested as a group with |
1082 | the :flock tag (or they can be requested individually, of course). |
1083 | LOCK_SH requests a shared lock, LOCK_EX requests an exclusive lock, and |
1084 | LOCK_UN releases a previously requested lock. If LOCK_NB is added to |
1085 | LOCK_SH or LOCK_EX then flock() will return immediately rather than |
1086 | blocking waiting for the lock (check the return status to see if you got |
1087 | it). |
1088 | |
1089 | Note that the emulation built with lockf(3) doesn't provide shared |
1090 | locks, and it requires that FILEHANDLE be open with write intent. These |
1091 | are the semantics that lockf(3) implements. Most (all?) systems |
1092 | implement lockf(3) in terms of fcntl(2) locking, though, so the |
1093 | differing semantics shouldn't bite too many people. |
1094 | |
1095 | Note also that some versions of flock() cannot lock things over the |
1096 | network; you would need to use the more system-specific fcntl() for |
1097 | that. If you like you can force Perl to ignore your system's flock(2) |
1098 | function, and so provide its own fcntl(2)-based emulation, by passing |
1099 | the switch C<-Ud_flock> to the F<Configure> program when you configure |
1100 | perl. |
4633a7c4 |
1101 | |
1102 | Here's a mailbox appender for BSD systems. |
a0d0e21e |
1103 | |
7e1af8bc |
1104 | use Fcntl ':flock'; # import LOCK_* constants |
a0d0e21e |
1105 | |
1106 | sub lock { |
7e1af8bc |
1107 | flock(MBOX,LOCK_EX); |
a0d0e21e |
1108 | # and, in case someone appended |
1109 | # while we were waiting... |
1110 | seek(MBOX, 0, 2); |
1111 | } |
1112 | |
1113 | sub unlock { |
7e1af8bc |
1114 | flock(MBOX,LOCK_UN); |
a0d0e21e |
1115 | } |
1116 | |
1117 | open(MBOX, ">>/usr/spool/mail/$ENV{'USER'}") |
1118 | or die "Can't open mailbox: $!"; |
1119 | |
1120 | lock(); |
1121 | print MBOX $msg,"\n\n"; |
1122 | unlock(); |
1123 | |
cb1a09d0 |
1124 | See also L<DB_File> for other flock() examples. |
a0d0e21e |
1125 | |
1126 | =item fork |
1127 | |
1128 | Does a fork(2) system call. Returns the child pid to the parent process |
4633a7c4 |
1129 | and 0 to the child process, or C<undef> if the fork is unsuccessful. |
a0d0e21e |
1130 | Note: unflushed buffers remain unflushed in both processes, which means |
28757baa |
1131 | you may need to set C<$|> ($AUTOFLUSH in English) or call the autoflush() |
1132 | method of IO::Handle to avoid duplicate output. |
a0d0e21e |
1133 | |
1134 | If you fork() without ever waiting on your children, you will accumulate |
1135 | zombies: |
1136 | |
4633a7c4 |
1137 | $SIG{CHLD} = sub { wait }; |
a0d0e21e |
1138 | |
1139 | There's also the double-fork trick (error checking on |
1140 | fork() returns omitted); |
1141 | |
1142 | unless ($pid = fork) { |
1143 | unless (fork) { |
1144 | exec "what you really wanna do"; |
1145 | die "no exec"; |
1146 | # ... or ... |
4633a7c4 |
1147 | ## (some_perl_code_here) |
a0d0e21e |
1148 | exit 0; |
1149 | } |
1150 | exit 0; |
1151 | } |
1152 | waitpid($pid,0); |
1153 | |
cb1a09d0 |
1154 | See also L<perlipc> for more examples of forking and reaping |
1155 | moribund children. |
1156 | |
28757baa |
1157 | Note that if your forked child inherits system file descriptors like |
1158 | STDIN and STDOUT that are actually connected by a pipe or socket, even |
1159 | if you exit, the remote server (such as, say, httpd or rsh) won't think |
1160 | you're done. You should reopen those to /dev/null if it's any issue. |
1161 | |
cb1a09d0 |
1162 | =item format |
1163 | |
1164 | Declare a picture format with use by the write() function. For |
1165 | example: |
1166 | |
1167 | format Something = |
1168 | Test: @<<<<<<<< @||||| @>>>>> |
1169 | $str, $%, '$' . int($num) |
1170 | . |
1171 | |
1172 | $str = "widget"; |
184e9718 |
1173 | $num = $cost/$quantity; |
cb1a09d0 |
1174 | $~ = 'Something'; |
1175 | write; |
1176 | |
1177 | See L<perlform> for many details and examples. |
1178 | |
a0d0e21e |
1179 | |
1180 | =item formline PICTURE, LIST |
1181 | |
4633a7c4 |
1182 | This is an internal function used by C<format>s, though you may call it |
a0d0e21e |
1183 | too. It formats (see L<perlform>) a list of values according to the |
1184 | contents of PICTURE, placing the output into the format output |
4633a7c4 |
1185 | accumulator, C<$^A> (or $ACCUMULATOR in English). |
1186 | Eventually, when a write() is done, the contents of |
a0d0e21e |
1187 | C<$^A> are written to some filehandle, but you could also read C<$^A> |
1188 | yourself and then set C<$^A> back to "". Note that a format typically |
1189 | does one formline() per line of form, but the formline() function itself |
748a9306 |
1190 | doesn't care how many newlines are embedded in the PICTURE. This means |
4633a7c4 |
1191 | that the C<~> and C<~~> tokens will treat the entire PICTURE as a single line. |
748a9306 |
1192 | You may therefore need to use multiple formlines to implement a single |
1193 | record format, just like the format compiler. |
1194 | |
5f05dabc |
1195 | Be careful if you put double quotes around the picture, because an "C<@>" |
748a9306 |
1196 | character may be taken to mean the beginning of an array name. |
4633a7c4 |
1197 | formline() always returns TRUE. See L<perlform> for other examples. |
a0d0e21e |
1198 | |
1199 | =item getc FILEHANDLE |
1200 | |
1201 | =item getc |
1202 | |
1203 | Returns the next character from the input file attached to FILEHANDLE, |
1204 | or a null string at end of file. If FILEHANDLE is omitted, reads from STDIN. |
4633a7c4 |
1205 | This is not particularly efficient. It cannot be used to get unbuffered |
cb1a09d0 |
1206 | single-characters, however. For that, try something more like: |
4633a7c4 |
1207 | |
1208 | if ($BSD_STYLE) { |
1209 | system "stty cbreak </dev/tty >/dev/tty 2>&1"; |
1210 | } |
1211 | else { |
cb1a09d0 |
1212 | system "stty", '-icanon', 'eol', "\001"; |
4633a7c4 |
1213 | } |
1214 | |
1215 | $key = getc(STDIN); |
1216 | |
1217 | if ($BSD_STYLE) { |
1218 | system "stty -cbreak </dev/tty >/dev/tty 2>&1"; |
1219 | } |
1220 | else { |
5f05dabc |
1221 | system "stty", 'icanon', 'eol', '^@'; # ASCII null |
4633a7c4 |
1222 | } |
1223 | print "\n"; |
1224 | |
1225 | Determination of whether to whether $BSD_STYLE should be set |
cb1a09d0 |
1226 | is left as an exercise to the reader. |
1227 | |
28757baa |
1228 | The POSIX::getattr() function can do this more portably on systems |
1229 | alleging POSIX compliance. |
cb1a09d0 |
1230 | See also the C<Term::ReadKey> module from your nearest CPAN site; |
28757baa |
1231 | details on CPAN can be found on L<perlmod/CPAN>. |
a0d0e21e |
1232 | |
1233 | =item getlogin |
1234 | |
1235 | Returns the current login from F</etc/utmp>, if any. If null, use |
4633a7c4 |
1236 | getpwuid(). |
a0d0e21e |
1237 | |
1238 | $login = getlogin || (getpwuid($<))[0] || "Kilroy"; |
1239 | |
da0045b7 |
1240 | Do not consider getlogin() for authentication: it is not as |
4633a7c4 |
1241 | secure as getpwuid(). |
1242 | |
a0d0e21e |
1243 | =item getpeername SOCKET |
1244 | |
1245 | Returns the packed sockaddr address of other end of the SOCKET connection. |
1246 | |
4633a7c4 |
1247 | use Socket; |
1248 | $hersockaddr = getpeername(SOCK); |
1249 | ($port, $iaddr) = unpack_sockaddr_in($hersockaddr); |
1250 | $herhostname = gethostbyaddr($iaddr, AF_INET); |
1251 | $herstraddr = inet_ntoa($iaddr); |
a0d0e21e |
1252 | |
1253 | =item getpgrp PID |
1254 | |
47e29363 |
1255 | Returns the current process group for the specified PID. Use |
1256 | a PID of 0 to get the current process group for the |
4633a7c4 |
1257 | current process. Will raise an exception if used on a machine that |
a0d0e21e |
1258 | doesn't implement getpgrp(2). If PID is omitted, returns process |
47e29363 |
1259 | group of current process. Note that the POSIX version of getpgrp() |
1260 | does not accept a PID argument, so only PID==0 is truly portable. |
a0d0e21e |
1261 | |
1262 | =item getppid |
1263 | |
1264 | Returns the process id of the parent process. |
1265 | |
1266 | =item getpriority WHICH,WHO |
1267 | |
4633a7c4 |
1268 | Returns the current priority for a process, a process group, or a user. |
1269 | (See L<getpriority(2)>.) Will raise a fatal exception if used on a |
a0d0e21e |
1270 | machine that doesn't implement getpriority(2). |
1271 | |
1272 | =item getpwnam NAME |
1273 | |
1274 | =item getgrnam NAME |
1275 | |
1276 | =item gethostbyname NAME |
1277 | |
1278 | =item getnetbyname NAME |
1279 | |
1280 | =item getprotobyname NAME |
1281 | |
1282 | =item getpwuid UID |
1283 | |
1284 | =item getgrgid GID |
1285 | |
1286 | =item getservbyname NAME,PROTO |
1287 | |
1288 | =item gethostbyaddr ADDR,ADDRTYPE |
1289 | |
1290 | =item getnetbyaddr ADDR,ADDRTYPE |
1291 | |
1292 | =item getprotobynumber NUMBER |
1293 | |
1294 | =item getservbyport PORT,PROTO |
1295 | |
1296 | =item getpwent |
1297 | |
1298 | =item getgrent |
1299 | |
1300 | =item gethostent |
1301 | |
1302 | =item getnetent |
1303 | |
1304 | =item getprotoent |
1305 | |
1306 | =item getservent |
1307 | |
1308 | =item setpwent |
1309 | |
1310 | =item setgrent |
1311 | |
1312 | =item sethostent STAYOPEN |
1313 | |
1314 | =item setnetent STAYOPEN |
1315 | |
1316 | =item setprotoent STAYOPEN |
1317 | |
1318 | =item setservent STAYOPEN |
1319 | |
1320 | =item endpwent |
1321 | |
1322 | =item endgrent |
1323 | |
1324 | =item endhostent |
1325 | |
1326 | =item endnetent |
1327 | |
1328 | =item endprotoent |
1329 | |
1330 | =item endservent |
1331 | |
1332 | These routines perform the same functions as their counterparts in the |
1333 | system library. Within a list context, the return values from the |
1334 | various get routines are as follows: |
1335 | |
1336 | ($name,$passwd,$uid,$gid, |
1337 | $quota,$comment,$gcos,$dir,$shell) = getpw* |
1338 | ($name,$passwd,$gid,$members) = getgr* |
1339 | ($name,$aliases,$addrtype,$length,@addrs) = gethost* |
1340 | ($name,$aliases,$addrtype,$net) = getnet* |
1341 | ($name,$aliases,$proto) = getproto* |
1342 | ($name,$aliases,$port,$proto) = getserv* |
1343 | |
1344 | (If the entry doesn't exist you get a null list.) |
1345 | |
1346 | Within a scalar context, you get the name, unless the function was a |
1347 | lookup by name, in which case you get the other thing, whatever it is. |
1348 | (If the entry doesn't exist you get the undefined value.) For example: |
1349 | |
1350 | $uid = getpwnam |
1351 | $name = getpwuid |
1352 | $name = getpwent |
1353 | $gid = getgrnam |
1354 | $name = getgrgid |
1355 | $name = getgrent |
1356 | etc. |
1357 | |
1358 | The $members value returned by I<getgr*()> is a space separated list of |
1359 | the login names of the members of the group. |
1360 | |
1361 | For the I<gethost*()> functions, if the C<h_errno> variable is supported in |
1362 | C, it will be returned to you via C<$?> if the function call fails. The |
1363 | @addrs value returned by a successful call is a list of the raw |
1364 | addresses returned by the corresponding system library call. In the |
1365 | Internet domain, each address is four bytes long and you can unpack it |
1366 | by saying something like: |
1367 | |
1368 | ($a,$b,$c,$d) = unpack('C4',$addr[0]); |
1369 | |
1370 | =item getsockname SOCKET |
1371 | |
1372 | Returns the packed sockaddr address of this end of the SOCKET connection. |
1373 | |
4633a7c4 |
1374 | use Socket; |
1375 | $mysockaddr = getsockname(SOCK); |
1376 | ($port, $myaddr) = unpack_sockaddr_in($mysockaddr); |
a0d0e21e |
1377 | |
1378 | =item getsockopt SOCKET,LEVEL,OPTNAME |
1379 | |
1380 | Returns the socket option requested, or undefined if there is an error. |
1381 | |
1382 | =item glob EXPR |
1383 | |
1384 | Returns the value of EXPR with filename expansions such as a shell |
184e9718 |
1385 | would do. This is the internal function implementing the E<lt>*.*E<gt> |
4633a7c4 |
1386 | operator, except it's easier to use. |
a0d0e21e |
1387 | |
1388 | =item gmtime EXPR |
1389 | |
1390 | Converts a time as returned by the time function to a 9-element array |
5f05dabc |
1391 | with the time localized for the standard Greenwich time zone. |
4633a7c4 |
1392 | Typically used as follows: |
a0d0e21e |
1393 | |
1394 | |
1395 | ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = |
1396 | gmtime(time); |
1397 | |
1398 | All array elements are numeric, and come straight out of a struct tm. |
1399 | In particular this means that $mon has the range 0..11 and $wday has |
1400 | the range 0..6. If EXPR is omitted, does C<gmtime(time())>. |
1401 | |
1402 | =item goto LABEL |
1403 | |
748a9306 |
1404 | =item goto EXPR |
1405 | |
a0d0e21e |
1406 | =item goto &NAME |
1407 | |
1408 | The goto-LABEL form finds the statement labeled with LABEL and resumes |
1409 | execution there. It may not be used to go into any construct that |
1410 | requires initialization, such as a subroutine or a foreach loop. It |
1411 | also can't be used to go into a construct that is optimized away. It |
1412 | can be used to go almost anywhere else within the dynamic scope, |
1413 | including out of subroutines, but it's usually better to use some other |
1414 | construct such as last or die. The author of Perl has never felt the |
1415 | need to use this form of goto (in Perl, that is--C is another matter). |
1416 | |
748a9306 |
1417 | The goto-EXPR form expects a label name, whose scope will be resolved |
1418 | dynamically. This allows for computed gotos per FORTRAN, but isn't |
1419 | necessarily recommended if you're optimizing for maintainability: |
1420 | |
1421 | goto ("FOO", "BAR", "GLARCH")[$i]; |
1422 | |
a0d0e21e |
1423 | The goto-&NAME form is highly magical, and substitutes a call to the |
1424 | named subroutine for the currently running subroutine. This is used by |
1425 | AUTOLOAD subroutines that wish to load another subroutine and then |
1426 | pretend that the other subroutine had been called in the first place |
1427 | (except that any modifications to @_ in the current subroutine are |
1428 | propagated to the other subroutine.) After the goto, not even caller() |
1429 | will be able to tell that this routine was called first. |
1430 | |
1431 | =item grep BLOCK LIST |
1432 | |
1433 | =item grep EXPR,LIST |
1434 | |
1435 | Evaluates the BLOCK or EXPR for each element of LIST (locally setting |
1436 | $_ to each element) and returns the list value consisting of those |
1437 | elements for which the expression evaluated to TRUE. In a scalar |
1438 | context, returns the number of times the expression was TRUE. |
1439 | |
1440 | @foo = grep(!/^#/, @bar); # weed out comments |
1441 | |
1442 | or equivalently, |
1443 | |
1444 | @foo = grep {!/^#/} @bar; # weed out comments |
1445 | |
5f05dabc |
1446 | Note that, because $_ is a reference into the list value, it can be used |
a0d0e21e |
1447 | to modify the elements of the array. While this is useful and |
1448 | supported, it can cause bizarre results if the LIST is not a named |
1449 | array. |
1450 | |
1451 | =item hex EXPR |
1452 | |
bbce6d69 |
1453 | =item hex |
1454 | |
4633a7c4 |
1455 | Interprets EXPR as a hex string and returns the corresponding decimal |
1456 | value. (To convert strings that might start with 0 or 0x see |
1457 | oct().) If EXPR is omitted, uses $_. |
a0d0e21e |
1458 | |
1459 | =item import |
1460 | |
1461 | There is no built-in import() function. It is merely an ordinary |
4633a7c4 |
1462 | method (subroutine) defined (or inherited) by modules that wish to export |
a0d0e21e |
1463 | names to another module. The use() function calls the import() method |
4633a7c4 |
1464 | for the package used. See also L</use>, L<perlmod>, and L<Exporter>. |
a0d0e21e |
1465 | |
1466 | =item index STR,SUBSTR,POSITION |
1467 | |
1468 | =item index STR,SUBSTR |
1469 | |
4633a7c4 |
1470 | Returns the position of the first occurrence of SUBSTR in STR at or after |
1471 | POSITION. If POSITION is omitted, starts searching from the beginning of |
184e9718 |
1472 | the string. The return value is based at 0 (or whatever you've set the C<$[> |
4633a7c4 |
1473 | variable to--but don't do that). If the substring is not found, returns |
a0d0e21e |
1474 | one less than the base, ordinarily -1. |
1475 | |
1476 | =item int EXPR |
1477 | |
bbce6d69 |
1478 | =item int |
1479 | |
a0d0e21e |
1480 | Returns the integer portion of EXPR. If EXPR is omitted, uses $_. |
1481 | |
1482 | =item ioctl FILEHANDLE,FUNCTION,SCALAR |
1483 | |
1484 | Implements the ioctl(2) function. You'll probably have to say |
1485 | |
4633a7c4 |
1486 | require "ioctl.ph"; # probably in /usr/local/lib/perl/ioctl.ph |
a0d0e21e |
1487 | |
4633a7c4 |
1488 | first to get the correct function definitions. If F<ioctl.ph> doesn't |
a0d0e21e |
1489 | exist or doesn't have the correct definitions you'll have to roll your |
4633a7c4 |
1490 | own, based on your C header files such as F<E<lt>sys/ioctl.hE<gt>>. |
1491 | (There is a Perl script called B<h2ph> that comes with the Perl kit which |
1492 | may help you in this, but it's non-trivial.) SCALAR will be read and/or |
1493 | written depending on the FUNCTION--a pointer to the string value of SCALAR |
1494 | will be passed as the third argument of the actual ioctl call. (If SCALAR |
1495 | has no string value but does have a numeric value, that value will be |
1496 | passed rather than a pointer to the string value. To guarantee this to be |
1497 | TRUE, add a 0 to the scalar before using it.) The pack() and unpack() |
1498 | functions are useful for manipulating the values of structures used by |
1499 | ioctl(). The following example sets the erase character to DEL. |
a0d0e21e |
1500 | |
1501 | require 'ioctl.ph'; |
4633a7c4 |
1502 | $getp = &TIOCGETP; |
1503 | die "NO TIOCGETP" if $@ || !$getp; |
a0d0e21e |
1504 | $sgttyb_t = "ccccs"; # 4 chars and a short |
4633a7c4 |
1505 | if (ioctl(STDIN,$getp,$sgttyb)) { |
a0d0e21e |
1506 | @ary = unpack($sgttyb_t,$sgttyb); |
1507 | $ary[2] = 127; |
1508 | $sgttyb = pack($sgttyb_t,@ary); |
4633a7c4 |
1509 | ioctl(STDIN,&TIOCSETP,$sgttyb) |
a0d0e21e |
1510 | || die "Can't ioctl: $!"; |
1511 | } |
1512 | |
1513 | The return value of ioctl (and fcntl) is as follows: |
1514 | |
1515 | if OS returns: then Perl returns: |
1516 | -1 undefined value |
1517 | 0 string "0 but true" |
1518 | anything else that number |
1519 | |
1520 | Thus Perl returns TRUE on success and FALSE on failure, yet you can |
1521 | still easily determine the actual value returned by the operating |
1522 | system: |
1523 | |
1524 | ($retval = ioctl(...)) || ($retval = -1); |
1525 | printf "System returned %d\n", $retval; |
1526 | |
1527 | =item join EXPR,LIST |
1528 | |
1529 | Joins the separate strings of LIST or ARRAY into a single string with |
1530 | fields separated by the value of EXPR, and returns the string. |
1531 | Example: |
1532 | |
1533 | $_ = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell); |
1534 | |
1535 | See L<perlfunc/split>. |
1536 | |
1537 | =item keys ASSOC_ARRAY |
1538 | |
1539 | Returns a normal array consisting of all the keys of the named |
1540 | associative array. (In a scalar context, returns the number of keys.) |
1541 | The keys are returned in an apparently random order, but it is the same |
1542 | order as either the values() or each() function produces (given that |
1543 | the associative array has not been modified). Here is yet another way |
1544 | to print your environment: |
1545 | |
1546 | @keys = keys %ENV; |
1547 | @values = values %ENV; |
1548 | while ($#keys >= 0) { |
1549 | print pop(@keys), '=', pop(@values), "\n"; |
1550 | } |
1551 | |
1552 | or how about sorted by key: |
1553 | |
1554 | foreach $key (sort(keys %ENV)) { |
1555 | print $key, '=', $ENV{$key}, "\n"; |
1556 | } |
1557 | |
4633a7c4 |
1558 | To sort an array by value, you'll need to use a C<sort{}> |
cb1a09d0 |
1559 | function. Here's a descending numeric sort of a hash by its values: |
4633a7c4 |
1560 | |
1561 | foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash)) { |
1562 | printf "%4d %s\n", $hash{$key}, $key; |
1563 | } |
1564 | |
55497cff |
1565 | As an lvalue C<keys> allows you to increase the number of hash buckets |
1566 | allocated for the given associative array. This can gain you a measure |
1567 | of efficiency if you know the hash is going to get big. (This is |
1568 | similar to pre-extending an array by assigning a larger number to |
1569 | $#array.) If you say |
1570 | |
1571 | keys %hash = 200; |
1572 | |
1573 | then C<%hash> will have at least 200 buckets allocated for it. These |
1574 | buckets will be retained even if you do C<%hash = ()>, use C<undef |
1575 | %hash> if you want to free the storage while C<%hash> is still in scope. |
1576 | You can't shrink the number of buckets allocated for the hash using |
1577 | C<keys> in this way (but you needn't worry about doing this by accident, |
1578 | as trying has no effect). |
1579 | |
a0d0e21e |
1580 | =item kill LIST |
1581 | |
4633a7c4 |
1582 | Sends a signal to a list of processes. The first element of |
1583 | the list must be the signal to send. Returns the number of |
1584 | processes successfully signaled. |
a0d0e21e |
1585 | |
1586 | $cnt = kill 1, $child1, $child2; |
1587 | kill 9, @goners; |
1588 | |
4633a7c4 |
1589 | Unlike in the shell, in Perl if the I<SIGNAL> is negative, it kills |
1590 | process groups instead of processes. (On System V, a negative I<PROCESS> |
1591 | number will also kill process groups, but that's not portable.) That |
1592 | means you usually want to use positive not negative signals. You may also |
da0045b7 |
1593 | use a signal name in quotes. See L<perlipc/"Signals"> for details. |
a0d0e21e |
1594 | |
1595 | =item last LABEL |
1596 | |
1597 | =item last |
1598 | |
1599 | The C<last> command is like the C<break> statement in C (as used in |
1600 | loops); it immediately exits the loop in question. If the LABEL is |
1601 | omitted, the command refers to the innermost enclosing loop. The |
1602 | C<continue> block, if any, is not executed: |
1603 | |
4633a7c4 |
1604 | LINE: while (<STDIN>) { |
1605 | last LINE if /^$/; # exit when done with header |
a0d0e21e |
1606 | ... |
1607 | } |
1608 | |
1609 | =item lc EXPR |
1610 | |
bbce6d69 |
1611 | =item lc |
1612 | |
a0d0e21e |
1613 | Returns an lowercased version of EXPR. This is the internal function |
4633a7c4 |
1614 | implementing the \L escape in double-quoted strings. |
a034a98d |
1615 | Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>. |
a0d0e21e |
1616 | |
bbce6d69 |
1617 | If EXPR is omitted, uses $_. |
1618 | |
a0d0e21e |
1619 | =item lcfirst EXPR |
1620 | |
bbce6d69 |
1621 | =item lcfirst |
1622 | |
a0d0e21e |
1623 | Returns the value of EXPR with the first character lowercased. This is |
1624 | the internal function implementing the \l escape in double-quoted strings. |
a034a98d |
1625 | Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>. |
a0d0e21e |
1626 | |
bbce6d69 |
1627 | If EXPR is omitted, uses $_. |
1628 | |
a0d0e21e |
1629 | =item length EXPR |
1630 | |
bbce6d69 |
1631 | =item length |
1632 | |
a0d0e21e |
1633 | Returns the length in characters of the value of EXPR. If EXPR is |
1634 | omitted, returns length of $_. |
1635 | |
1636 | =item link OLDFILE,NEWFILE |
1637 | |
1638 | Creates a new filename linked to the old filename. Returns 1 for |
1639 | success, 0 otherwise. |
1640 | |
1641 | =item listen SOCKET,QUEUESIZE |
1642 | |
1643 | Does the same thing that the listen system call does. Returns TRUE if |
4633a7c4 |
1644 | it succeeded, FALSE otherwise. See example in L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e |
1645 | |
1646 | =item local EXPR |
1647 | |
a0d0e21e |
1648 | A local modifies the listed variables to be local to the enclosing block, |
5f05dabc |
1649 | subroutine, C<eval{}>, or C<do>. If more than one value is listed, the |
1650 | list must be placed in parentheses. See L<perlsub/"Temporary Values via |
cb1a09d0 |
1651 | local()"> for details. |
a0d0e21e |
1652 | |
cb1a09d0 |
1653 | But you really probably want to be using my() instead, because local() isn't |
1654 | what most people think of as "local"). See L<perlsub/"Private Variables |
1655 | via my()"> for details. |
a0d0e21e |
1656 | |
1657 | =item localtime EXPR |
1658 | |
1659 | Converts a time as returned by the time function to a 9-element array |
5f05dabc |
1660 | with the time analyzed for the local time zone. Typically used as |
a0d0e21e |
1661 | follows: |
1662 | |
1663 | ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) = |
1664 | localtime(time); |
1665 | |
1666 | All array elements are numeric, and come straight out of a struct tm. |
1667 | In particular this means that $mon has the range 0..11 and $wday has |
1668 | the range 0..6. If EXPR is omitted, does localtime(time). |
1669 | |
1670 | In a scalar context, prints out the ctime(3) value: |
1671 | |
5f05dabc |
1672 | $now_string = localtime; # e.g., "Thu Oct 13 04:54:34 1994" |
a0d0e21e |
1673 | |
37798a01 |
1674 | Also see the F<timelocal.pl> library, and the strftime(3) function available |
da0045b7 |
1675 | via the POSIX module. |
a0d0e21e |
1676 | |
1677 | =item log EXPR |
1678 | |
bbce6d69 |
1679 | =item log |
1680 | |
a0d0e21e |
1681 | Returns logarithm (base I<e>) of EXPR. If EXPR is omitted, returns log |
1682 | of $_. |
1683 | |
1684 | =item lstat FILEHANDLE |
1685 | |
1686 | =item lstat EXPR |
1687 | |
bbce6d69 |
1688 | =item lstat |
1689 | |
a0d0e21e |
1690 | Does the same thing as the stat() function, but stats a symbolic link |
1691 | instead of the file the symbolic link points to. If symbolic links are |
1692 | unimplemented on your system, a normal stat() is done. |
1693 | |
bbce6d69 |
1694 | If EXPR is omitted, stats $_. |
1695 | |
a0d0e21e |
1696 | =item m// |
1697 | |
1698 | The match operator. See L<perlop>. |
1699 | |
1700 | =item map BLOCK LIST |
1701 | |
1702 | =item map EXPR,LIST |
1703 | |
1704 | Evaluates the BLOCK or EXPR for each element of LIST (locally setting $_ to each |
1705 | element) and returns the list value composed of the results of each such |
1706 | evaluation. Evaluates BLOCK or EXPR in a list context, so each element of LIST |
1707 | may produce zero, one, or more elements in the returned value. |
1708 | |
1709 | @chars = map(chr, @nums); |
1710 | |
1711 | translates a list of numbers to the corresponding characters. And |
1712 | |
4633a7c4 |
1713 | %hash = map { getkey($_) => $_ } @array; |
a0d0e21e |
1714 | |
1715 | is just a funny way to write |
1716 | |
1717 | %hash = (); |
1718 | foreach $_ (@array) { |
4633a7c4 |
1719 | $hash{getkey($_)} = $_; |
a0d0e21e |
1720 | } |
1721 | |
1722 | =item mkdir FILENAME,MODE |
1723 | |
1724 | Creates the directory specified by FILENAME, with permissions specified |
1725 | by MODE (as modified by umask). If it succeeds it returns 1, otherwise |
184e9718 |
1726 | it returns 0 and sets C<$!> (errno). |
a0d0e21e |
1727 | |
1728 | =item msgctl ID,CMD,ARG |
1729 | |
4633a7c4 |
1730 | Calls the System V IPC function msgctl(2). If CMD is &IPC_STAT, then ARG |
a0d0e21e |
1731 | must be a variable which will hold the returned msqid_ds structure. |
1732 | Returns like ioctl: the undefined value for error, "0 but true" for |
1733 | zero, or the actual return value otherwise. |
1734 | |
1735 | =item msgget KEY,FLAGS |
1736 | |
4633a7c4 |
1737 | Calls the System V IPC function msgget(2). Returns the message queue id, |
a0d0e21e |
1738 | or the undefined value if there is an error. |
1739 | |
1740 | =item msgsnd ID,MSG,FLAGS |
1741 | |
1742 | Calls the System V IPC function msgsnd to send the message MSG to the |
1743 | message queue ID. MSG must begin with the long integer message type, |
c07a80fd |
1744 | which may be created with C<pack("l", $type)>. Returns TRUE if |
a0d0e21e |
1745 | successful, or FALSE if there is an error. |
1746 | |
1747 | =item msgrcv ID,VAR,SIZE,TYPE,FLAGS |
1748 | |
1749 | Calls the System V IPC function msgrcv to receive a message from |
1750 | message queue ID into variable VAR with a maximum message size of |
1751 | SIZE. Note that if a message is received, the message type will be the |
1752 | first thing in VAR, and the maximum length of VAR is SIZE plus the size |
1753 | of the message type. Returns TRUE if successful, or FALSE if there is |
1754 | an error. |
1755 | |
1756 | =item my EXPR |
1757 | |
1758 | A "my" declares the listed variables to be local (lexically) to the |
cb1a09d0 |
1759 | enclosing block, subroutine, C<eval>, or C<do/require/use>'d file. If |
5f05dabc |
1760 | more than one value is listed, the list must be placed in parentheses. See |
cb1a09d0 |
1761 | L<perlsub/"Private Variables via my()"> for details. |
4633a7c4 |
1762 | |
a0d0e21e |
1763 | =item next LABEL |
1764 | |
1765 | =item next |
1766 | |
1767 | The C<next> command is like the C<continue> statement in C; it starts |
1768 | the next iteration of the loop: |
1769 | |
4633a7c4 |
1770 | LINE: while (<STDIN>) { |
1771 | next LINE if /^#/; # discard comments |
a0d0e21e |
1772 | ... |
1773 | } |
1774 | |
1775 | Note that if there were a C<continue> block on the above, it would get |
1776 | executed even on discarded lines. If the LABEL is omitted, the command |
1777 | refers to the innermost enclosing loop. |
1778 | |
1779 | =item no Module LIST |
1780 | |
1781 | See the "use" function, which "no" is the opposite of. |
1782 | |
1783 | =item oct EXPR |
1784 | |
bbce6d69 |
1785 | =item oct |
1786 | |
4633a7c4 |
1787 | Interprets EXPR as an octal string and returns the corresponding |
1788 | decimal value. (If EXPR happens to start off with 0x, interprets it as |
1789 | a hex string instead.) The following will handle decimal, octal, and |
1790 | hex in the standard Perl or C notation: |
a0d0e21e |
1791 | |
1792 | $val = oct($val) if $val =~ /^0/; |
1793 | |
1794 | If EXPR is omitted, uses $_. |
1795 | |
1796 | =item open FILEHANDLE,EXPR |
1797 | |
1798 | =item open FILEHANDLE |
1799 | |
1800 | Opens the file whose filename is given by EXPR, and associates it with |
5f05dabc |
1801 | FILEHANDLE. If FILEHANDLE is an expression, its value is used as the |
1802 | name of the real filehandle wanted. If EXPR is omitted, the scalar |
1803 | variable of the same name as the FILEHANDLE contains the filename. |
1804 | (Note that lexical variables--those declared with C<my>--will not work |
1805 | for this purpose; so if you're using C<my>, specify EXPR in your call |
1806 | to open.) |
1807 | |
1808 | If the filename begins with '<' or nothing, the file is opened for input. |
1809 | If the filename begins with '>', the file is truncated and opened for |
1810 | output. If the filename begins with '>>', the file is opened for |
1811 | appending. You can put a '+' in front of the '>' or '<' to indicate that |
1812 | you want both read and write access to the file; thus '+<' is almost |
1813 | always preferred for read/write updates--the '+>' mode would clobber the |
1814 | file first. The prefix and the filename may be separated with spaces. |
1815 | These various prefixes correspond to the fopen(3) modes of 'r', 'r+', 'w', |
1816 | 'w+', 'a', and 'a+'. |
1817 | |
1818 | If the filename begins with "|", the filename is interpreted as a command |
1819 | to which output is to be piped, and if the filename ends with a "|", the |
1820 | filename is interpreted See L<perlipc/"Using open() for IPC"> for more |
1821 | examples of this. as command which pipes input to us. (You may not have |
7e1af8bc |
1822 | a raw open() to a command that pipes both in I<and> out, but see |
1823 | L<IPC::Open2>, L<IPC::Open3>, and L<perlipc/"Bidirectional Communication"> |
1824 | for alternatives.) |
cb1a09d0 |
1825 | |
184e9718 |
1826 | Opening '-' opens STDIN and opening 'E<gt>-' opens STDOUT. Open returns |
4633a7c4 |
1827 | non-zero upon success, the undefined value otherwise. If the open |
1828 | involved a pipe, the return value happens to be the pid of the |
cb1a09d0 |
1829 | subprocess. |
1830 | |
1831 | If you're unfortunate enough to be running Perl on a system that |
1832 | distinguishes between text files and binary files (modern operating |
1833 | systems don't care), then you should check out L</binmode> for tips for |
1834 | dealing with this. The key distinction between systems that need binmode |
1835 | and those that don't is their text file formats. Systems like Unix and |
1836 | Plan9 that delimit lines with a single character, and that encode that |
1837 | character in C as '\n', do not need C<binmode>. The rest need it. |
1838 | |
cb1a09d0 |
1839 | Examples: |
a0d0e21e |
1840 | |
1841 | $ARTICLE = 100; |
1842 | open ARTICLE or die "Can't find article $ARTICLE: $!\n"; |
1843 | while (<ARTICLE>) {... |
1844 | |
1845 | open(LOG, '>>/usr/spool/news/twitlog'); # (log is reserved) |
1846 | |
cb1a09d0 |
1847 | open(DBASE, '+<dbase.mine'); # open for update |
1848 | |
4633a7c4 |
1849 | open(ARTICLE, "caesar <$article |"); # decrypt article |
a0d0e21e |
1850 | |
4633a7c4 |
1851 | open(EXTRACT, "|sort >/tmp/Tmp$$"); # $$ is our process id |
a0d0e21e |
1852 | |
1853 | # process argument list of files along with any includes |
1854 | |
1855 | foreach $file (@ARGV) { |
1856 | process($file, 'fh00'); |
1857 | } |
1858 | |
1859 | sub process { |
1860 | local($filename, $input) = @_; |
1861 | $input++; # this is a string increment |
1862 | unless (open($input, $filename)) { |
1863 | print STDERR "Can't open $filename: $!\n"; |
1864 | return; |
1865 | } |
1866 | |
1867 | while (<$input>) { # note use of indirection |
1868 | if (/^#include "(.*)"/) { |
1869 | process($1, $input); |
1870 | next; |
1871 | } |
1872 | ... # whatever |
1873 | } |
1874 | } |
1875 | |
1876 | You may also, in the Bourne shell tradition, specify an EXPR beginning |
184e9718 |
1877 | with "E<gt>&", in which case the rest of the string is interpreted as the |
a0d0e21e |
1878 | name of a filehandle (or file descriptor, if numeric) which is to be |
184e9718 |
1879 | duped and opened. You may use & after E<gt>, E<gt>E<gt>, E<lt>, +E<gt>, |
5f05dabc |
1880 | +E<gt>E<gt>, and +E<lt>. The |
a0d0e21e |
1881 | mode you specify should match the mode of the original filehandle. |
184e9718 |
1882 | (Duping a filehandle does not take into account any existing contents of |
cb1a09d0 |
1883 | stdio buffers.) |
a0d0e21e |
1884 | Here is a script that saves, redirects, and restores STDOUT and |
1885 | STDERR: |
1886 | |
1887 | #!/usr/bin/perl |
1888 | open(SAVEOUT, ">&STDOUT"); |
1889 | open(SAVEERR, ">&STDERR"); |
1890 | |
1891 | open(STDOUT, ">foo.out") || die "Can't redirect stdout"; |
1892 | open(STDERR, ">&STDOUT") || die "Can't dup stdout"; |
1893 | |
1894 | select(STDERR); $| = 1; # make unbuffered |
1895 | select(STDOUT); $| = 1; # make unbuffered |
1896 | |
1897 | print STDOUT "stdout 1\n"; # this works for |
1898 | print STDERR "stderr 1\n"; # subprocesses too |
1899 | |
1900 | close(STDOUT); |
1901 | close(STDERR); |
1902 | |
1903 | open(STDOUT, ">&SAVEOUT"); |
1904 | open(STDERR, ">&SAVEERR"); |
1905 | |
1906 | print STDOUT "stdout 2\n"; |
1907 | print STDERR "stderr 2\n"; |
1908 | |
1909 | |
184e9718 |
1910 | If you specify "E<lt>&=N", where N is a number, then Perl will do an |
4633a7c4 |
1911 | equivalent of C's fdopen() of that file descriptor; this is more |
1912 | parsimonious of file descriptors. For example: |
a0d0e21e |
1913 | |
1914 | open(FILEHANDLE, "<&=$fd") |
1915 | |
5f05dabc |
1916 | If you open a pipe on the command "-", i.e., either "|-" or "-|", then |
a0d0e21e |
1917 | there is an implicit fork done, and the return value of open is the pid |
1918 | of the child within the parent process, and 0 within the child |
184e9718 |
1919 | process. (Use C<defined($pid)> to determine whether the open was successful.) |
a0d0e21e |
1920 | The filehandle behaves normally for the parent, but i/o to that |
1921 | filehandle is piped from/to the STDOUT/STDIN of the child process. |
1922 | In the child process the filehandle isn't opened--i/o happens from/to |
1923 | the new STDOUT or STDIN. Typically this is used like the normal |
1924 | piped open when you want to exercise more control over just how the |
1925 | pipe command gets executed, such as when you are running setuid, and |
4633a7c4 |
1926 | don't want to have to scan shell commands for metacharacters. |
1927 | The following pairs are more or less equivalent: |
a0d0e21e |
1928 | |
1929 | open(FOO, "|tr '[a-z]' '[A-Z]'"); |
1930 | open(FOO, "|-") || exec 'tr', '[a-z]', '[A-Z]'; |
1931 | |
1932 | open(FOO, "cat -n '$file'|"); |
1933 | open(FOO, "-|") || exec 'cat', '-n', $file; |
1934 | |
4633a7c4 |
1935 | See L<perlipc/"Safe Pipe Opens"> for more examples of this. |
1936 | |
a0d0e21e |
1937 | Explicitly closing any piped filehandle causes the parent process to |
184e9718 |
1938 | wait for the child to finish, and returns the status value in C<$?>. |
a0d0e21e |
1939 | Note: on any operation which may do a fork, unflushed buffers remain |
184e9718 |
1940 | unflushed in both processes, which means you may need to set C<$|> to |
a0d0e21e |
1941 | avoid duplicate output. |
1942 | |
5f05dabc |
1943 | Using the constructor from the IO::Handle package (or one of its |
1944 | subclasses, such as IO::File or IO::Socket), |
c07a80fd |
1945 | you can generate anonymous filehandles which have the scope of whatever |
1946 | variables hold references to them, and automatically close whenever |
1947 | and however you leave that scope: |
1948 | |
5f05dabc |
1949 | use IO::File; |
c07a80fd |
1950 | ... |
1951 | sub read_myfile_munged { |
1952 | my $ALL = shift; |
5f05dabc |
1953 | my $handle = new IO::File; |
c07a80fd |
1954 | open($handle, "myfile") or die "myfile: $!"; |
1955 | $first = <$handle> |
1956 | or return (); # Automatically closed here. |
1957 | mung $first or die "mung failed"; # Or here. |
1958 | return $first, <$handle> if $ALL; # Or here. |
1959 | $first; # Or here. |
1960 | } |
1961 | |
a0d0e21e |
1962 | The filename that is passed to open will have leading and trailing |
5f05dabc |
1963 | whitespace deleted. To open a file with arbitrary weird |
a0d0e21e |
1964 | characters in it, it's necessary to protect any leading and trailing |
1965 | whitespace thusly: |
1966 | |
cb1a09d0 |
1967 | $file =~ s#^(\s)#./$1#; |
1968 | open(FOO, "< $file\0"); |
1969 | |
c07a80fd |
1970 | If you want a "real" C open() (see L<open(2)> on your system), then |
1971 | you should use the sysopen() function. This is another way to |
1972 | protect your filenames from interpretation. For example: |
cb1a09d0 |
1973 | |
28757baa |
1974 | use IO::Handle; |
c07a80fd |
1975 | sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL, 0700) |
1976 | or die "sysopen $path: $!"; |
1977 | HANDLE->autoflush(1); |
1978 | HANDLE->print("stuff $$\n"); |
1979 | seek(HANDLE, 0, 0); |
1980 | print "File contains: ", <HANDLE>; |
cb1a09d0 |
1981 | |
1982 | See L</seek()> for some details about mixing reading and writing. |
a0d0e21e |
1983 | |
1984 | =item opendir DIRHANDLE,EXPR |
1985 | |
1986 | Opens a directory named EXPR for processing by readdir(), telldir(), |
5f05dabc |
1987 | seekdir(), rewinddir(), and closedir(). Returns TRUE if successful. |
a0d0e21e |
1988 | DIRHANDLEs have their own namespace separate from FILEHANDLEs. |
1989 | |
1990 | =item ord EXPR |
1991 | |
bbce6d69 |
1992 | =item ord |
1993 | |
a0d0e21e |
1994 | Returns the numeric ascii value of the first character of EXPR. If |
1995 | EXPR is omitted, uses $_. |
1996 | |
1997 | =item pack TEMPLATE,LIST |
1998 | |
1999 | Takes an array or list of values and packs it into a binary structure, |
2000 | returning the string containing the structure. The TEMPLATE is a |
2001 | sequence of characters that give the order and type of values, as |
2002 | follows: |
2003 | |
2004 | A An ascii string, will be space padded. |
2005 | a An ascii string, will be null padded. |
2006 | b A bit string (ascending bit order, like vec()). |
2007 | B A bit string (descending bit order). |
2008 | h A hex string (low nybble first). |
2009 | H A hex string (high nybble first). |
2010 | |
2011 | c A signed char value. |
2012 | C An unsigned char value. |
2013 | s A signed short value. |
2014 | S An unsigned short value. |
2015 | i A signed integer value. |
2016 | I An unsigned integer value. |
2017 | l A signed long value. |
2018 | L An unsigned long value. |
2019 | |
2020 | n A short in "network" order. |
2021 | N A long in "network" order. |
2022 | v A short in "VAX" (little-endian) order. |
2023 | V A long in "VAX" (little-endian) order. |
2024 | |
2025 | f A single-precision float in the native format. |
2026 | d A double-precision float in the native format. |
2027 | |
2028 | p A pointer to a null-terminated string. |
2029 | P A pointer to a structure (fixed-length string). |
2030 | |
2031 | u A uuencoded string. |
2032 | |
def98dd4 |
2033 | w A BER compressed integer. Bytes give an unsigned integer base |
2034 | 128, most significant digit first, with as few digits as |
2035 | possible, and with the bit 8 of each byte except the last set |
2036 | to "1." |
2037 | |
a0d0e21e |
2038 | x A null byte. |
2039 | X Back up a byte. |
2040 | @ Null fill to absolute position. |
2041 | |
2042 | Each letter may optionally be followed by a number which gives a repeat |
5f05dabc |
2043 | count. With all types except "a", "A", "b", "B", "h", "H", and "P" the |
a0d0e21e |
2044 | pack function will gobble up that many values from the LIST. A * for the |
2045 | repeat count means to use however many items are left. The "a" and "A" |
2046 | types gobble just one value, but pack it as a string of length count, |
2047 | padding with nulls or spaces as necessary. (When unpacking, "A" strips |
2048 | trailing spaces and nulls, but "a" does not.) Likewise, the "b" and "B" |
2049 | fields pack a string that many bits long. The "h" and "H" fields pack a |
2050 | string that many nybbles long. The "P" packs a pointer to a structure of |
2051 | the size indicated by the length. Real numbers (floats and doubles) are |
2052 | in the native machine format only; due to the multiplicity of floating |
2053 | formats around, and the lack of a standard "network" representation, no |
2054 | facility for interchange has been made. This means that packed floating |
2055 | point data written on one machine may not be readable on another - even if |
2056 | both use IEEE floating point arithmetic (as the endian-ness of the memory |
2057 | representation is not part of the IEEE spec). Note that Perl uses doubles |
2058 | internally for all numeric calculation, and converting from double into |
5f05dabc |
2059 | float and thence back to double again will lose precision (i.e., |
a0d0e21e |
2060 | C<unpack("f", pack("f", $foo)>) will not in general equal $foo). |
2061 | |
2062 | Examples: |
2063 | |
2064 | $foo = pack("cccc",65,66,67,68); |
2065 | # foo eq "ABCD" |
2066 | $foo = pack("c4",65,66,67,68); |
2067 | # same thing |
2068 | |
2069 | $foo = pack("ccxxcc",65,66,67,68); |
2070 | # foo eq "AB\0\0CD" |
2071 | |
2072 | $foo = pack("s2",1,2); |
2073 | # "\1\0\2\0" on little-endian |
2074 | # "\0\1\0\2" on big-endian |
2075 | |
2076 | $foo = pack("a4","abcd","x","y","z"); |
2077 | # "abcd" |
2078 | |
2079 | $foo = pack("aaaa","abcd","x","y","z"); |
2080 | # "axyz" |
2081 | |
2082 | $foo = pack("a14","abcdefg"); |
2083 | # "abcdefg\0\0\0\0\0\0\0" |
2084 | |
2085 | $foo = pack("i9pl", gmtime); |
2086 | # a real struct tm (on my system anyway) |
2087 | |
2088 | sub bintodec { |
2089 | unpack("N", pack("B32", substr("0" x 32 . shift, -32))); |
2090 | } |
2091 | |
2092 | The same template may generally also be used in the unpack function. |
2093 | |
cb1a09d0 |
2094 | =item package NAMESPACE |
2095 | |
2096 | Declares the compilation unit as being in the given namespace. The scope |
2097 | of the package declaration is from the declaration itself through the end of |
2098 | the enclosing block (the same scope as the local() operator). All further |
2099 | unqualified dynamic identifiers will be in this namespace. A package |
5f05dabc |
2100 | statement affects only dynamic variables--including those you've used |
cb1a09d0 |
2101 | local() on--but I<not> lexical variables created with my(). Typically it |
2102 | would be the first declaration in a file to be included by the C<require> |
2103 | or C<use> operator. You can switch into a package in more than one place; |
5f05dabc |
2104 | it influences merely which symbol table is used by the compiler for the |
cb1a09d0 |
2105 | rest of that block. You can refer to variables and filehandles in other |
2106 | packages by prefixing the identifier with the package name and a double |
2107 | colon: C<$Package::Variable>. If the package name is null, the C<main> |
2108 | package as assumed. That is, C<$::sail> is equivalent to C<$main::sail>. |
2109 | |
2110 | See L<perlmod/"Packages"> for more information about packages, modules, |
2111 | and classes. See L<perlsub> for other scoping issues. |
2112 | |
a0d0e21e |
2113 | =item pipe READHANDLE,WRITEHANDLE |
2114 | |
2115 | Opens a pair of connected pipes like the corresponding system call. |
2116 | Note that if you set up a loop of piped processes, deadlock can occur |
2117 | unless you are very careful. In addition, note that Perl's pipes use |
184e9718 |
2118 | stdio buffering, so you may need to set C<$|> to flush your WRITEHANDLE |
a0d0e21e |
2119 | after each command, depending on the application. |
2120 | |
7e1af8bc |
2121 | See L<IPC::Open2>, L<IPC::Open3>, and L<perlipc/"Bidirectional Communication"> |
4633a7c4 |
2122 | for examples of such things. |
2123 | |
a0d0e21e |
2124 | =item pop ARRAY |
2125 | |
28757baa |
2126 | =item pop |
2127 | |
a0d0e21e |
2128 | Pops and returns the last value of the array, shortening the array by |
2129 | 1. Has a similar effect to |
2130 | |
2131 | $tmp = $ARRAY[$#ARRAY--]; |
2132 | |
2133 | If there are no elements in the array, returns the undefined value. |
cb1a09d0 |
2134 | If ARRAY is omitted, pops the |
2135 | @ARGV array in the main program, and the @_ array in subroutines, just |
2136 | like shift(). |
a0d0e21e |
2137 | |
2138 | =item pos SCALAR |
2139 | |
bbce6d69 |
2140 | =item pos |
2141 | |
4633a7c4 |
2142 | Returns the offset of where the last C<m//g> search left off for the variable |
bbce6d69 |
2143 | is in question ($_ is used when the variable is not specified). May be |
44a8e56a |
2144 | modified to change that offset. Such modification will also influence |
2145 | the C<\G> zero-width assertion in regular expressions. See L<perlre> and |
2146 | L<perlop>. |
a0d0e21e |
2147 | |
2148 | =item print FILEHANDLE LIST |
2149 | |
2150 | =item print LIST |
2151 | |
2152 | =item print |
2153 | |
cb1a09d0 |
2154 | Prints a string or a comma-separated list of strings. Returns TRUE |
a0d0e21e |
2155 | if successful. FILEHANDLE may be a scalar variable name, in which case |
cb1a09d0 |
2156 | the variable contains the name of or a reference to the filehandle, thus introducing one |
a0d0e21e |
2157 | level of indirection. (NOTE: If FILEHANDLE is a variable and the next |
2158 | token is a term, it may be misinterpreted as an operator unless you |
5f05dabc |
2159 | interpose a + or put parentheses around the arguments.) If FILEHANDLE is |
a0d0e21e |
2160 | omitted, prints by default to standard output (or to the last selected |
da0045b7 |
2161 | output channel--see L</select>). If LIST is also omitted, prints $_ to |
a0d0e21e |
2162 | STDOUT. To set the default output channel to something other than |
2163 | STDOUT use the select operation. Note that, because print takes a |
2164 | LIST, anything in the LIST is evaluated in a list context, and any |
2165 | subroutine that you call will have one or more of its expressions |
2166 | evaluated in a list context. Also be careful not to follow the print |
2167 | keyword with a left parenthesis unless you want the corresponding right |
2168 | parenthesis to terminate the arguments to the print--interpose a + or |
5f05dabc |
2169 | put parentheses around all the arguments. |
a0d0e21e |
2170 | |
4633a7c4 |
2171 | Note that if you're storing FILEHANDLES in an array or other expression, |
da0045b7 |
2172 | you will have to use a block returning its value instead: |
4633a7c4 |
2173 | |
2174 | print { $files[$i] } "stuff\n"; |
2175 | print { $OK ? STDOUT : STDERR } "stuff\n"; |
2176 | |
5f05dabc |
2177 | =item printf FILEHANDLE FORMAT, LIST |
a0d0e21e |
2178 | |
5f05dabc |
2179 | =item printf FORMAT, LIST |
a0d0e21e |
2180 | |
a034a98d |
2181 | Equivalent to C<print FILEHANDLE sprintf(FORMAT, LIST)>. The first argument |
2182 | of the list will be interpreted as the printf format. If C<use locale> is |
2183 | in effect, the character used for the decimal point in formatted real numbers |
2184 | is affected by the LC_NUMERIC locale. See L<perllocale>. |
a0d0e21e |
2185 | |
28757baa |
2186 | Don't fall into the trap of using a printf() when a simple |
2187 | print() would do. The print() is more efficient, and less |
2188 | error prone. |
2189 | |
da0045b7 |
2190 | =item prototype FUNCTION |
2191 | |
2192 | Returns the prototype of a function as a string (or C<undef> if the |
5f05dabc |
2193 | function has no prototype). FUNCTION is a reference to, or the name of, |
2194 | the function whose prototype you want to retrieve. |
da0045b7 |
2195 | |
a0d0e21e |
2196 | =item push ARRAY,LIST |
2197 | |
2198 | Treats ARRAY as a stack, and pushes the values of LIST |
2199 | onto the end of ARRAY. The length of ARRAY increases by the length of |
2200 | LIST. Has the same effect as |
2201 | |
2202 | for $value (LIST) { |
2203 | $ARRAY[++$#ARRAY] = $value; |
2204 | } |
2205 | |
2206 | but is more efficient. Returns the new number of elements in the array. |
2207 | |
2208 | =item q/STRING/ |
2209 | |
2210 | =item qq/STRING/ |
2211 | |
2212 | =item qx/STRING/ |
2213 | |
2214 | =item qw/STRING/ |
2215 | |
2216 | Generalized quotes. See L<perlop>. |
2217 | |
2218 | =item quotemeta EXPR |
2219 | |
bbce6d69 |
2220 | =item quotemeta |
2221 | |
a034a98d |
2222 | Returns the value of EXPR with with all non-alphanumeric |
2223 | characters backslashed. (That is, all characters not matching |
2224 | C</[A-Za-z_0-9]/> will be preceded by a backslash in the |
2225 | returned string, regardless of any locale settings.) |
2226 | This is the internal function implementing |
a0d0e21e |
2227 | the \Q escape in double-quoted strings. |
2228 | |
bbce6d69 |
2229 | If EXPR is omitted, uses $_. |
2230 | |
a0d0e21e |
2231 | =item rand EXPR |
2232 | |
2233 | =item rand |
2234 | |
2235 | Returns a random fractional number between 0 and the value of EXPR. |
2236 | (EXPR should be positive.) If EXPR is omitted, returns a value between |
2237 | 0 and 1. This function produces repeatable sequences unless srand() |
2238 | is invoked. See also srand(). |
2239 | |
2240 | (Note: if your rand function consistently returns numbers that are too |
2241 | large or too small, then your version of Perl was probably compiled |
2242 | with the wrong number of RANDBITS. As a workaround, you can usually |
2243 | multiply EXPR by the correct power of 2 to get the range you want. |
2244 | This will make your script unportable, however. It's better to recompile |
2245 | if you can.) |
2246 | |
2247 | =item read FILEHANDLE,SCALAR,LENGTH,OFFSET |
2248 | |
2249 | =item read FILEHANDLE,SCALAR,LENGTH |
2250 | |
2251 | Attempts to read LENGTH bytes of data into variable SCALAR from the |
2252 | specified FILEHANDLE. Returns the number of bytes actually read, or |
2253 | undef if there was an error. SCALAR will be grown or shrunk to the |
2254 | length actually read. An OFFSET may be specified to place the read |
2255 | data at some other place than the beginning of the string. This call |
2256 | is actually implemented in terms of stdio's fread call. To get a true |
2257 | read system call, see sysread(). |
2258 | |
2259 | =item readdir DIRHANDLE |
2260 | |
2261 | Returns the next directory entry for a directory opened by opendir(). |
2262 | If used in a list context, returns all the rest of the entries in the |
2263 | directory. If there are no more entries, returns an undefined value in |
2264 | a scalar context or a null list in a list context. |
2265 | |
cb1a09d0 |
2266 | If you're planning to filetest the return values out of a readdir(), you'd |
5f05dabc |
2267 | better prepend the directory in question. Otherwise, because we didn't |
cb1a09d0 |
2268 | chdir() there, it would have been testing the wrong file. |
2269 | |
2270 | opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!"; |
2271 | @dots = grep { /^\./ && -f "$some_dir/$_" } readdir(DIR); |
2272 | closedir DIR; |
2273 | |
a0d0e21e |
2274 | =item readlink EXPR |
2275 | |
bbce6d69 |
2276 | =item readlink |
2277 | |
a0d0e21e |
2278 | Returns the value of a symbolic link, if symbolic links are |
2279 | implemented. If not, gives a fatal error. If there is some system |
184e9718 |
2280 | error, returns the undefined value and sets C<$!> (errno). If EXPR is |
a0d0e21e |
2281 | omitted, uses $_. |
2282 | |
2283 | =item recv SOCKET,SCALAR,LEN,FLAGS |
2284 | |
2285 | Receives a message on a socket. Attempts to receive LENGTH bytes of |
2286 | data into variable SCALAR from the specified SOCKET filehandle. |
2287 | Actually does a C recvfrom(), so that it can returns the address of the |
2288 | sender. Returns the undefined value if there's an error. SCALAR will |
2289 | be grown or shrunk to the length actually read. Takes the same flags |
4633a7c4 |
2290 | as the system call of the same name. |
2291 | See L<perlipc/"UDP: Message Passing"> for examples. |
a0d0e21e |
2292 | |
2293 | =item redo LABEL |
2294 | |
2295 | =item redo |
2296 | |
2297 | The C<redo> command restarts the loop block without evaluating the |
2298 | conditional again. The C<continue> block, if any, is not executed. If |
2299 | the LABEL is omitted, the command refers to the innermost enclosing |
2300 | loop. This command is normally used by programs that want to lie to |
2301 | themselves about what was just input: |
2302 | |
2303 | # a simpleminded Pascal comment stripper |
2304 | # (warning: assumes no { or } in strings) |
4633a7c4 |
2305 | LINE: while (<STDIN>) { |
a0d0e21e |
2306 | while (s|({.*}.*){.*}|$1 |) {} |
2307 | s|{.*}| |; |
2308 | if (s|{.*| |) { |
2309 | $front = $_; |
2310 | while (<STDIN>) { |
2311 | if (/}/) { # end of comment? |
2312 | s|^|$front{|; |
4633a7c4 |
2313 | redo LINE; |
a0d0e21e |
2314 | } |
2315 | } |
2316 | } |
2317 | print; |
2318 | } |
2319 | |
2320 | =item ref EXPR |
2321 | |
bbce6d69 |
2322 | =item ref |
2323 | |
2324 | Returns a TRUE value if EXPR is a reference, FALSE otherwise. If EXPR |
2325 | is not specified, $_ will be used. The value returned depends on the |
2326 | type of thing the reference is a reference to. |
a0d0e21e |
2327 | Builtin types include: |
2328 | |
2329 | REF |
2330 | SCALAR |
2331 | ARRAY |
2332 | HASH |
2333 | CODE |
2334 | GLOB |
2335 | |
2336 | If the referenced object has been blessed into a package, then that package |
2337 | name is returned instead. You can think of ref() as a typeof() operator. |
2338 | |
2339 | if (ref($r) eq "HASH") { |
2340 | print "r is a reference to an associative array.\n"; |
2341 | } |
2342 | if (!ref ($r) { |
2343 | print "r is not a reference at all.\n"; |
2344 | } |
2345 | |
2346 | See also L<perlref>. |
2347 | |
2348 | =item rename OLDNAME,NEWNAME |
2349 | |
2350 | Changes the name of a file. Returns 1 for success, 0 otherwise. Will |
5f05dabc |
2351 | not work across file system boundaries. |
a0d0e21e |
2352 | |
2353 | =item require EXPR |
2354 | |
2355 | =item require |
2356 | |
2357 | Demands some semantics specified by EXPR, or by $_ if EXPR is not |
2358 | supplied. If EXPR is numeric, demands that the current version of Perl |
184e9718 |
2359 | (C<$]> or $PERL_VERSION) be equal or greater than EXPR. |
a0d0e21e |
2360 | |
2361 | Otherwise, demands that a library file be included if it hasn't already |
2362 | been included. The file is included via the do-FILE mechanism, which is |
2363 | essentially just a variety of eval(). Has semantics similar to the following |
2364 | subroutine: |
2365 | |
2366 | sub require { |
2367 | local($filename) = @_; |
2368 | return 1 if $INC{$filename}; |
2369 | local($realfilename,$result); |
2370 | ITER: { |
2371 | foreach $prefix (@INC) { |
2372 | $realfilename = "$prefix/$filename"; |
2373 | if (-f $realfilename) { |
2374 | $result = do $realfilename; |
2375 | last ITER; |
2376 | } |
2377 | } |
2378 | die "Can't find $filename in \@INC"; |
2379 | } |
2380 | die $@ if $@; |
2381 | die "$filename did not return true value" unless $result; |
2382 | $INC{$filename} = $realfilename; |
2383 | $result; |
2384 | } |
2385 | |
2386 | Note that the file will not be included twice under the same specified |
2387 | name. The file must return TRUE as the last statement to indicate |
2388 | successful execution of any initialization code, so it's customary to |
2389 | end such a file with "1;" unless you're sure it'll return TRUE |
2390 | otherwise. But it's better just to put the "C<1;>", in case you add more |
2391 | statements. |
2392 | |
da0045b7 |
2393 | If EXPR is a bare word, the require assumes a "F<.pm>" extension and |
2394 | replaces "F<::>" with "F</>" in the filename for you, |
a0d0e21e |
2395 | to make it easy to load standard modules. This form of loading of |
2396 | modules does not risk altering your namespace. |
2397 | |
da0045b7 |
2398 | For a yet-more-powerful import facility, see L</use> and |
748a9306 |
2399 | L<perlmod>. |
a0d0e21e |
2400 | |
2401 | =item reset EXPR |
2402 | |
2403 | =item reset |
2404 | |
2405 | Generally used in a C<continue> block at the end of a loop to clear |
2406 | variables and reset ?? searches so that they work again. The |
2407 | expression is interpreted as a list of single characters (hyphens |
2408 | allowed for ranges). All variables and arrays beginning with one of |
2409 | those letters are reset to their pristine state. If the expression is |
5f05dabc |
2410 | omitted, one-match searches (?pattern?) are reset to match again. Resets |
2411 | only variables or searches in the current package. Always returns |
a0d0e21e |
2412 | 1. Examples: |
2413 | |
2414 | reset 'X'; # reset all X variables |
2415 | reset 'a-z'; # reset lower case variables |
2416 | reset; # just reset ?? searches |
2417 | |
5f05dabc |
2418 | Resetting "A-Z" is not recommended because you'll wipe out your |
2419 | ARGV and ENV arrays. Resets only package variables--lexical variables |
a0d0e21e |
2420 | are unaffected, but they clean themselves up on scope exit anyway, |
da0045b7 |
2421 | so you'll probably want to use them instead. See L</my>. |
a0d0e21e |
2422 | |
2423 | =item return LIST |
2424 | |
2425 | Returns from a subroutine or eval with the value specified. (Note that |
4633a7c4 |
2426 | in the absence of a return a subroutine or eval() will automatically |
a0d0e21e |
2427 | return the value of the last expression evaluated.) |
2428 | |
2429 | =item reverse LIST |
2430 | |
2431 | In a list context, returns a list value consisting of the elements |
2432 | of LIST in the opposite order. In a scalar context, returns a string |
2433 | value consisting of the bytes of the first element of LIST in the |
4633a7c4 |
2434 | opposite order. |
2435 | |
2436 | print reverse <>; # line tac |
2437 | |
2438 | undef $/; |
2439 | print scalar reverse scalar <>; # byte tac |
a0d0e21e |
2440 | |
2441 | =item rewinddir DIRHANDLE |
2442 | |
2443 | Sets the current position to the beginning of the directory for the |
2444 | readdir() routine on DIRHANDLE. |
2445 | |
2446 | =item rindex STR,SUBSTR,POSITION |
2447 | |
2448 | =item rindex STR,SUBSTR |
2449 | |
2450 | Works just like index except that it returns the position of the LAST |
2451 | occurrence of SUBSTR in STR. If POSITION is specified, returns the |
2452 | last occurrence at or before that position. |
2453 | |
2454 | =item rmdir FILENAME |
2455 | |
bbce6d69 |
2456 | =item rmdir |
2457 | |
a0d0e21e |
2458 | Deletes the directory specified by FILENAME if it is empty. If it |
184e9718 |
2459 | succeeds it returns 1, otherwise it returns 0 and sets C<$!> (errno). If |
a0d0e21e |
2460 | FILENAME is omitted, uses $_. |
2461 | |
2462 | =item s/// |
2463 | |
2464 | The substitution operator. See L<perlop>. |
2465 | |
2466 | =item scalar EXPR |
2467 | |
2468 | Forces EXPR to be interpreted in a scalar context and returns the value |
cb1a09d0 |
2469 | of EXPR. |
2470 | |
2471 | @counts = ( scalar @a, scalar @b, scalar @c ); |
2472 | |
2473 | There is no equivalent operator to force an expression to |
2474 | be interpolated in a list context because it's in practice never |
2475 | needed. If you really wanted to do so, however, you could use |
2476 | the construction C<@{[ (some expression) ]}>, but usually a simple |
2477 | C<(some expression)> suffices. |
a0d0e21e |
2478 | |
2479 | =item seek FILEHANDLE,POSITION,WHENCE |
2480 | |
2481 | Randomly positions the file pointer for FILEHANDLE, just like the fseek() |
2482 | call of stdio. FILEHANDLE may be an expression whose value gives the name |
2483 | of the filehandle. The values for WHENCE are 0 to set the file pointer to |
2484 | POSITION, 1 to set the it to current plus POSITION, and 2 to set it to EOF |
2485 | plus offset. You may use the values SEEK_SET, SEEK_CUR, and SEEK_END for |
4633a7c4 |
2486 | this from POSIX module. Returns 1 upon success, 0 otherwise. |
a0d0e21e |
2487 | |
cb1a09d0 |
2488 | On some systems you have to do a seek whenever you switch between reading |
2489 | and writing. Amongst other things, this may have the effect of calling |
2490 | stdio's clearerr(3). A "whence" of 1 (SEEK_CUR) is useful for not moving |
2491 | the file pointer: |
2492 | |
2493 | seek(TEST,0,1); |
2494 | |
2495 | This is also useful for applications emulating C<tail -f>. Once you hit |
2496 | EOF on your read, and then sleep for a while, you might have to stick in a |
2497 | seek() to reset things. First the simple trick listed above to clear the |
2498 | filepointer. The seek() doesn't change the current position, but it |
2499 | I<does> clear the end-of-file condition on the handle, so that the next |
5f05dabc |
2500 | C<E<lt>FILEE<gt>> makes Perl try again to read something. We hope. |
cb1a09d0 |
2501 | |
2502 | If that doesn't work (some stdios are particularly cantankerous), then |
2503 | you may need something more like this: |
2504 | |
2505 | for (;;) { |
2506 | for ($curpos = tell(FILE); $_ = <FILE>; $curpos = tell(FILE)) { |
2507 | # search for some stuff and put it into files |
2508 | } |
2509 | sleep($for_a_while); |
2510 | seek(FILE, $curpos, 0); |
2511 | } |
2512 | |
a0d0e21e |
2513 | =item seekdir DIRHANDLE,POS |
2514 | |
2515 | Sets the current position for the readdir() routine on DIRHANDLE. POS |
2516 | must be a value returned by telldir(). Has the same caveats about |
2517 | possible directory compaction as the corresponding system library |
2518 | routine. |
2519 | |
2520 | =item select FILEHANDLE |
2521 | |
2522 | =item select |
2523 | |
2524 | Returns the currently selected filehandle. Sets the current default |
2525 | filehandle for output, if FILEHANDLE is supplied. This has two |
2526 | effects: first, a C<write> or a C<print> without a filehandle will |
2527 | default to this FILEHANDLE. Second, references to variables related to |
2528 | output will refer to this output channel. For example, if you have to |
2529 | set the top of form format for more than one output channel, you might |
2530 | do the following: |
2531 | |
2532 | select(REPORT1); |
2533 | $^ = 'report1_top'; |
2534 | select(REPORT2); |
2535 | $^ = 'report2_top'; |
2536 | |
2537 | FILEHANDLE may be an expression whose value gives the name of the |
2538 | actual filehandle. Thus: |
2539 | |
2540 | $oldfh = select(STDERR); $| = 1; select($oldfh); |
2541 | |
4633a7c4 |
2542 | Some programmers may prefer to think of filehandles as objects with |
2543 | methods, preferring to write the last example as: |
a0d0e21e |
2544 | |
28757baa |
2545 | use IO::Handle; |
a0d0e21e |
2546 | STDERR->autoflush(1); |
2547 | |
2548 | =item select RBITS,WBITS,EBITS,TIMEOUT |
2549 | |
5f05dabc |
2550 | This calls the select(2) system call with the bit masks specified, which |
a0d0e21e |
2551 | can be constructed using fileno() and vec(), along these lines: |
2552 | |
2553 | $rin = $win = $ein = ''; |
2554 | vec($rin,fileno(STDIN),1) = 1; |
2555 | vec($win,fileno(STDOUT),1) = 1; |
2556 | $ein = $rin | $win; |
2557 | |
2558 | If you want to select on many filehandles you might wish to write a |
2559 | subroutine: |
2560 | |
2561 | sub fhbits { |
2562 | local(@fhlist) = split(' ',$_[0]); |
2563 | local($bits); |
2564 | for (@fhlist) { |
2565 | vec($bits,fileno($_),1) = 1; |
2566 | } |
2567 | $bits; |
2568 | } |
4633a7c4 |
2569 | $rin = fhbits('STDIN TTY SOCK'); |
a0d0e21e |
2570 | |
2571 | The usual idiom is: |
2572 | |
2573 | ($nfound,$timeleft) = |
2574 | select($rout=$rin, $wout=$win, $eout=$ein, $timeout); |
2575 | |
c07a80fd |
2576 | or to block until something becomes ready just do this |
a0d0e21e |
2577 | |
2578 | $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef); |
2579 | |
5f05dabc |
2580 | Most systems do not bother to return anything useful in $timeleft, so |
c07a80fd |
2581 | calling select() in a scalar context just returns $nfound. |
2582 | |
5f05dabc |
2583 | Any of the bit masks can also be undef. The timeout, if specified, is |
a0d0e21e |
2584 | in seconds, which may be fractional. Note: not all implementations are |
2585 | capable of returning the $timeleft. If not, they always return |
2586 | $timeleft equal to the supplied $timeout. |
2587 | |
ff68c719 |
2588 | You can effect a sleep of 250 milliseconds this way: |
a0d0e21e |
2589 | |
2590 | select(undef, undef, undef, 0.25); |
2591 | |
184e9718 |
2592 | B<WARNING>: Do not attempt to mix buffered I/O (like read() or E<lt>FHE<gt>) |
cb1a09d0 |
2593 | with select(). You have to use sysread() instead. |
a0d0e21e |
2594 | |
2595 | =item semctl ID,SEMNUM,CMD,ARG |
2596 | |
2597 | Calls the System V IPC function semctl. If CMD is &IPC_STAT or |
2598 | &GETALL, then ARG must be a variable which will hold the returned |
2599 | semid_ds structure or semaphore value array. Returns like ioctl: the |
2600 | undefined value for error, "0 but true" for zero, or the actual return |
2601 | value otherwise. |
2602 | |
2603 | =item semget KEY,NSEMS,FLAGS |
2604 | |
2605 | Calls the System V IPC function semget. Returns the semaphore id, or |
2606 | the undefined value if there is an error. |
2607 | |
2608 | =item semop KEY,OPSTRING |
2609 | |
2610 | Calls the System V IPC function semop to perform semaphore operations |
2611 | such as signaling and waiting. OPSTRING must be a packed array of |
2612 | semop structures. Each semop structure can be generated with |
2613 | C<pack("sss", $semnum, $semop, $semflag)>. The number of semaphore |
2614 | operations is implied by the length of OPSTRING. Returns TRUE if |
2615 | successful, or FALSE if there is an error. As an example, the |
2616 | following code waits on semaphore $semnum of semaphore id $semid: |
2617 | |
2618 | $semop = pack("sss", $semnum, -1, 0); |
2619 | die "Semaphore trouble: $!\n" unless semop($semid, $semop); |
2620 | |
2621 | To signal the semaphore, replace "-1" with "1". |
2622 | |
2623 | =item send SOCKET,MSG,FLAGS,TO |
2624 | |
2625 | =item send SOCKET,MSG,FLAGS |
2626 | |
2627 | Sends a message on a socket. Takes the same flags as the system call |
2628 | of the same name. On unconnected sockets you must specify a |
2629 | destination to send TO, in which case it does a C sendto(). Returns |
2630 | the number of characters sent, or the undefined value if there is an |
2631 | error. |
4633a7c4 |
2632 | See L<perlipc/"UDP: Message Passing"> for examples. |
a0d0e21e |
2633 | |
2634 | =item setpgrp PID,PGRP |
2635 | |
2636 | Sets the current process group for the specified PID, 0 for the current |
2637 | process. Will produce a fatal error if used on a machine that doesn't |
5f05dabc |
2638 | implement setpgrp(2). If the arguments are omitted, it defaults to |
47e29363 |
2639 | 0,0. Note that the POSIX version of setpgrp() does not accept any |
2640 | arguments, so only setpgrp 0,0 is portable. |
a0d0e21e |
2641 | |
2642 | =item setpriority WHICH,WHO,PRIORITY |
2643 | |
2644 | Sets the current priority for a process, a process group, or a user. |
748a9306 |
2645 | (See setpriority(2).) Will produce a fatal error if used on a machine |
a0d0e21e |
2646 | that doesn't implement setpriority(2). |
2647 | |
2648 | =item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL |
2649 | |
2650 | Sets the socket option requested. Returns undefined if there is an |
2651 | error. OPTVAL may be specified as undef if you don't want to pass an |
2652 | argument. |
2653 | |
2654 | =item shift ARRAY |
2655 | |
2656 | =item shift |
2657 | |
2658 | Shifts the first value of the array off and returns it, shortening the |
2659 | array by 1 and moving everything down. If there are no elements in the |
2660 | array, returns the undefined value. If ARRAY is omitted, shifts the |
2661 | @ARGV array in the main program, and the @_ array in subroutines. |
2662 | (This is determined lexically.) See also unshift(), push(), and pop(). |
2663 | Shift() and unshift() do the same thing to the left end of an array |
2664 | that push() and pop() do to the right end. |
2665 | |
2666 | =item shmctl ID,CMD,ARG |
2667 | |
2668 | Calls the System V IPC function shmctl. If CMD is &IPC_STAT, then ARG |
2669 | must be a variable which will hold the returned shmid_ds structure. |
2670 | Returns like ioctl: the undefined value for error, "0 but true" for |
2671 | zero, or the actual return value otherwise. |
2672 | |
2673 | =item shmget KEY,SIZE,FLAGS |
2674 | |
2675 | Calls the System V IPC function shmget. Returns the shared memory |
2676 | segment id, or the undefined value if there is an error. |
2677 | |
2678 | =item shmread ID,VAR,POS,SIZE |
2679 | |
2680 | =item shmwrite ID,STRING,POS,SIZE |
2681 | |
2682 | Reads or writes the System V shared memory segment ID starting at |
2683 | position POS for size SIZE by attaching to it, copying in/out, and |
2684 | detaching from it. When reading, VAR must be a variable which will |
2685 | hold the data read. When writing, if STRING is too long, only SIZE |
2686 | bytes are used; if STRING is too short, nulls are written to fill out |
2687 | SIZE bytes. Return TRUE if successful, or FALSE if there is an error. |
2688 | |
2689 | =item shutdown SOCKET,HOW |
2690 | |
2691 | Shuts down a socket connection in the manner indicated by HOW, which |
2692 | has the same interpretation as in the system call of the same name. |
2693 | |
2694 | =item sin EXPR |
2695 | |
bbce6d69 |
2696 | =item sin |
2697 | |
a0d0e21e |
2698 | Returns the sine of EXPR (expressed in radians). If EXPR is omitted, |
2699 | returns sine of $_. |
2700 | |
28757baa |
2701 | For the inverse sine operation, you may use the POSIX::sin() |
2702 | function, or use this relation: |
2703 | |
2704 | sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) } |
2705 | |
a0d0e21e |
2706 | =item sleep EXPR |
2707 | |
2708 | =item sleep |
2709 | |
2710 | Causes the script to sleep for EXPR seconds, or forever if no EXPR. |
2711 | May be interrupted by sending the process a SIGALRM. Returns the |
2712 | number of seconds actually slept. You probably cannot mix alarm() and |
5f05dabc |
2713 | sleep() calls, because sleep() is often implemented using alarm(). |
a0d0e21e |
2714 | |
2715 | On some older systems, it may sleep up to a full second less than what |
2716 | you requested, depending on how it counts seconds. Most modern systems |
2717 | always sleep the full amount. |
2718 | |
cb1a09d0 |
2719 | For delays of finer granularity than one second, you may use Perl's |
2720 | syscall() interface to access setitimer(2) if your system supports it, |
2721 | or else see L</select()> below. |
2722 | |
5f05dabc |
2723 | See also the POSIX module's sigpause() function. |
2724 | |
a0d0e21e |
2725 | =item socket SOCKET,DOMAIN,TYPE,PROTOCOL |
2726 | |
2727 | Opens a socket of the specified kind and attaches it to filehandle |
5f05dabc |
2728 | SOCKET. DOMAIN, TYPE, and PROTOCOL are specified the same as for the |
a0d0e21e |
2729 | system call of the same name. You should "use Socket;" first to get |
4633a7c4 |
2730 | the proper definitions imported. See the example in L<perlipc/"Sockets: Client/Server Communication">. |
a0d0e21e |
2731 | |
2732 | =item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL |
2733 | |
2734 | Creates an unnamed pair of sockets in the specified domain, of the |
5f05dabc |
2735 | specified type. DOMAIN, TYPE, and PROTOCOL are specified the same as |
a0d0e21e |
2736 | for the system call of the same name. If unimplemented, yields a fatal |
2737 | error. Returns TRUE if successful. |
2738 | |
2739 | =item sort SUBNAME LIST |
2740 | |
2741 | =item sort BLOCK LIST |
2742 | |
2743 | =item sort LIST |
2744 | |
2745 | Sorts the LIST and returns the sorted list value. Nonexistent values |
2746 | of arrays are stripped out. If SUBNAME or BLOCK is omitted, sorts |
2747 | in standard string comparison order. If SUBNAME is specified, it |
2748 | gives the name of a subroutine that returns an integer less than, equal |
2749 | to, or greater than 0, depending on how the elements of the array are |
184e9718 |
2750 | to be ordered. (The E<lt>=E<gt> and cmp operators are extremely useful in such |
a0d0e21e |
2751 | routines.) SUBNAME may be a scalar variable name, in which case the |
2752 | value provides the name of the subroutine to use. In place of a |
2753 | SUBNAME, you can provide a BLOCK as an anonymous, in-line sort |
2754 | subroutine. |
2755 | |
cb1a09d0 |
2756 | In the interests of efficiency the normal calling code for subroutines is |
2757 | bypassed, with the following effects: the subroutine may not be a |
2758 | recursive subroutine, and the two elements to be compared are passed into |
2759 | the subroutine not via @_ but as the package global variables $a and |
2760 | $b (see example below). They are passed by reference, so don't |
2761 | modify $a and $b. And don't try to declare them as lexicals either. |
a0d0e21e |
2762 | |
a034a98d |
2763 | When C<use locale> is in effect, C<sort LIST> sorts LIST according to the |
2764 | current collation locale. See L<perllocale>. |
2765 | |
a0d0e21e |
2766 | Examples: |
2767 | |
2768 | # sort lexically |
2769 | @articles = sort @files; |
2770 | |
2771 | # same thing, but with explicit sort routine |
2772 | @articles = sort {$a cmp $b} @files; |
2773 | |
cb1a09d0 |
2774 | # now case-insensitively |
2775 | @articles = sort { uc($a) cmp uc($b)} @files; |
2776 | |
a0d0e21e |
2777 | # same thing in reversed order |
2778 | @articles = sort {$b cmp $a} @files; |
2779 | |
2780 | # sort numerically ascending |
2781 | @articles = sort {$a <=> $b} @files; |
2782 | |
2783 | # sort numerically descending |
2784 | @articles = sort {$b <=> $a} @files; |
2785 | |
2786 | # sort using explicit subroutine name |
2787 | sub byage { |
2788 | $age{$a} <=> $age{$b}; # presuming integers |
2789 | } |
2790 | @sortedclass = sort byage @class; |
2791 | |
c07a80fd |
2792 | # this sorts the %age associative arrays by value |
5f05dabc |
2793 | # instead of key using an in-line function |
c07a80fd |
2794 | @eldest = sort { $age{$b} <=> $age{$a} } keys %age; |
2795 | |
a0d0e21e |
2796 | sub backwards { $b cmp $a; } |
2797 | @harry = ('dog','cat','x','Cain','Abel'); |
2798 | @george = ('gone','chased','yz','Punished','Axed'); |
2799 | print sort @harry; |
2800 | # prints AbelCaincatdogx |
2801 | print sort backwards @harry; |
2802 | # prints xdogcatCainAbel |
2803 | print sort @george, 'to', @harry; |
2804 | # prints AbelAxedCainPunishedcatchaseddoggonetoxyz |
2805 | |
cb1a09d0 |
2806 | # inefficiently sort by descending numeric compare using |
2807 | # the first integer after the first = sign, or the |
2808 | # whole record case-insensitively otherwise |
2809 | |
2810 | @new = sort { |
2811 | ($b =~ /=(\d+)/)[0] <=> ($a =~ /=(\d+)/)[0] |
2812 | || |
2813 | uc($a) cmp uc($b) |
2814 | } @old; |
2815 | |
2816 | # same thing, but much more efficiently; |
2817 | # we'll build auxiliary indices instead |
2818 | # for speed |
2819 | @nums = @caps = (); |
2820 | for (@old) { |
2821 | push @nums, /=(\d+)/; |
2822 | push @caps, uc($_); |
2823 | } |
2824 | |
2825 | @new = @old[ sort { |
2826 | $nums[$b] <=> $nums[$a] |
2827 | || |
2828 | $caps[$a] cmp $caps[$b] |
2829 | } 0..$#old |
2830 | ]; |
2831 | |
2832 | # same thing using a Schwartzian Transform (no temps) |
2833 | @new = map { $_->[0] } |
2834 | sort { $b->[1] <=> $a->[1] |
2835 | || |
2836 | $a->[2] cmp $b->[2] |
2837 | } map { [$_, /=(\d+)/, uc($_)] } @old; |
2838 | |
184e9718 |
2839 | If you're using strict, you I<MUST NOT> declare $a |
cb1a09d0 |
2840 | and $b as lexicals. They are package globals. That means |
2841 | if you're in the C<main> package, it's |
2842 | |
2843 | @articles = sort {$main::b <=> $main::a} @files; |
2844 | |
2845 | or just |
2846 | |
2847 | @articles = sort {$::b <=> $::a} @files; |
2848 | |
2849 | but if you're in the C<FooPack> package, it's |
2850 | |
2851 | @articles = sort {$FooPack::b <=> $FooPack::a} @files; |
2852 | |
55497cff |
2853 | The comparison function is required to behave. If it returns |
2854 | inconsistent results (sometimes saying $x[1] is less than $x[2] and |
2855 | sometimes saying the opposite, for example) the Perl interpreter will |
2856 | probably crash and dump core. This is entirely due to and dependent |
2857 | upon your system's qsort(3) library routine; this routine often avoids |
2858 | sanity checks in the interest of speed. |
2859 | |
a0d0e21e |
2860 | =item splice ARRAY,OFFSET,LENGTH,LIST |
2861 | |
2862 | =item splice ARRAY,OFFSET,LENGTH |
2863 | |
2864 | =item splice ARRAY,OFFSET |
2865 | |
2866 | Removes the elements designated by OFFSET and LENGTH from an array, and |
2867 | replaces them with the elements of LIST, if any. Returns the elements |
2868 | removed from the array. The array grows or shrinks as necessary. If |
2869 | LENGTH is omitted, removes everything from OFFSET onward. The |
5f05dabc |
2870 | following equivalences hold (assuming C<$[ == 0>): |
a0d0e21e |
2871 | |
2872 | push(@a,$x,$y) splice(@a,$#a+1,0,$x,$y) |
2873 | pop(@a) splice(@a,-1) |
2874 | shift(@a) splice(@a,0,1) |
2875 | unshift(@a,$x,$y) splice(@a,0,0,$x,$y) |
2876 | $a[$x] = $y splice(@a,$x,1,$y); |
2877 | |
2878 | Example, assuming array lengths are passed before arrays: |
2879 | |
2880 | sub aeq { # compare two list values |
2881 | local(@a) = splice(@_,0,shift); |
2882 | local(@b) = splice(@_,0,shift); |
2883 | return 0 unless @a == @b; # same len? |
2884 | while (@a) { |
2885 | return 0 if pop(@a) ne pop(@b); |
2886 | } |
2887 | return 1; |
2888 | } |
2889 | if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... } |
2890 | |
2891 | =item split /PATTERN/,EXPR,LIMIT |
2892 | |
2893 | =item split /PATTERN/,EXPR |
2894 | |
2895 | =item split /PATTERN/ |
2896 | |
2897 | =item split |
2898 | |
2899 | Splits a string into an array of strings, and returns it. |
2900 | |
2901 | If not in a list context, returns the number of fields found and splits into |
2902 | the @_ array. (In a list context, you can force the split into @_ by |
2903 | using C<??> as the pattern delimiters, but it still returns the array |
2904 | value.) The use of implicit split to @_ is deprecated, however. |
2905 | |
2906 | If EXPR is omitted, splits the $_ string. If PATTERN is also omitted, |
4633a7c4 |
2907 | splits on whitespace (after skipping any leading whitespace). Anything |
2908 | matching PATTERN is taken to be a delimiter separating the fields. (Note |
2909 | that the delimiter may be longer than one character.) If LIMIT is |
2910 | specified and is not negative, splits into no more than that many fields |
2911 | (though it may split into fewer). If LIMIT is unspecified, trailing null |
2912 | fields are stripped (which potential users of pop() would do well to |
2913 | remember). If LIMIT is negative, it is treated as if an arbitrarily large |
2914 | LIMIT had been specified. |
a0d0e21e |
2915 | |
2916 | A pattern matching the null string (not to be confused with |
748a9306 |
2917 | a null pattern C<//>, which is just one member of the set of patterns |
a0d0e21e |
2918 | matching a null string) will split the value of EXPR into separate |
2919 | characters at each point it matches that way. For example: |
2920 | |
2921 | print join(':', split(/ */, 'hi there')); |
2922 | |
2923 | produces the output 'h:i:t:h:e:r:e'. |
2924 | |
5f05dabc |
2925 | The LIMIT parameter can be used to split a line partially |
a0d0e21e |
2926 | |
2927 | ($login, $passwd, $remainder) = split(/:/, $_, 3); |
2928 | |
2929 | When assigning to a list, if LIMIT is omitted, Perl supplies a LIMIT |
2930 | one larger than the number of variables in the list, to avoid |
2931 | unnecessary work. For the list above LIMIT would have been 4 by |
2932 | default. In time critical applications it behooves you not to split |
2933 | into more fields than you really need. |
2934 | |
2935 | If the PATTERN contains parentheses, additional array elements are |
2936 | created from each matching substring in the delimiter. |
2937 | |
da0045b7 |
2938 | split(/([,-])/, "1-10,20", 3); |
a0d0e21e |
2939 | |
2940 | produces the list value |
2941 | |
2942 | (1, '-', 10, ',', 20) |
2943 | |
4633a7c4 |
2944 | If you had the entire header of a normal Unix email message in $header, |
2945 | you could split it up into fields and their values this way: |
2946 | |
2947 | $header =~ s/\n\s+/ /g; # fix continuation lines |
2948 | %hdrs = (UNIX_FROM => split /^(.*?):\s*/m, $header); |
2949 | |
a0d0e21e |
2950 | The pattern C</PATTERN/> may be replaced with an expression to specify |
2951 | patterns that vary at runtime. (To do runtime compilation only once, |
748a9306 |
2952 | use C</$variable/o>.) |
2953 | |
2954 | As a special case, specifying a PATTERN of space (C<' '>) will split on |
2955 | white space just as split with no arguments does. Thus, split(' ') can |
2956 | be used to emulate B<awk>'s default behavior, whereas C<split(/ /)> |
2957 | will give you as many null initial fields as there are leading spaces. |
2958 | A split on /\s+/ is like a split(' ') except that any leading |
2959 | whitespace produces a null first field. A split with no arguments |
2960 | really does a C<split(' ', $_)> internally. |
a0d0e21e |
2961 | |
2962 | Example: |
2963 | |
2964 | open(passwd, '/etc/passwd'); |
2965 | while (<passwd>) { |
748a9306 |
2966 | ($login, $passwd, $uid, $gid, $gcos, |
2967 | $home, $shell) = split(/:/); |
a0d0e21e |
2968 | ... |
2969 | } |
2970 | |
2971 | (Note that $shell above will still have a newline on it. See L</chop>, |
2972 | L</chomp>, and L</join>.) |
2973 | |
5f05dabc |
2974 | =item sprintf FORMAT, LIST |
a0d0e21e |
2975 | |
2976 | Returns a string formatted by the usual printf conventions of the C |
cb1a09d0 |
2977 | language. See L<sprintf(3)> or L<printf(3)> on your system for details. |
2978 | (The * character for an indirectly specified length is not |
a0d0e21e |
2979 | supported, but you can get the same effect by interpolating a variable |
a034a98d |
2980 | into the pattern.) If C<use locale> is |
2981 | in effect, the character used for the decimal point in formatted real numbers |
2982 | is affected by the LC_NUMERIC locale. See L<perllocale>. |
2983 | Some C libraries' implementations of sprintf() can |
cb1a09d0 |
2984 | dump core when fed ludicrous arguments. |
a0d0e21e |
2985 | |
2986 | =item sqrt EXPR |
2987 | |
bbce6d69 |
2988 | =item sqrt |
2989 | |
a0d0e21e |
2990 | Return the square root of EXPR. If EXPR is omitted, returns square |
2991 | root of $_. |
2992 | |
2993 | =item srand EXPR |
2994 | |
cb1a09d0 |
2995 | Sets the random number seed for the C<rand> operator. If EXPR is omitted, |
5f05dabc |
2996 | uses a semi-random value based on the current time and process ID, among |
0078ec44 |
2997 | other things. In versions of Perl prior to 5.004 the default seed was |
2998 | just the current time(). This isn't a particularly good seed, so many |
2999 | old programs supply their own seed value (often C<time ^ $$> or C<time ^ |
3000 | ($$ + ($$ << 15))>), but that isn't necessary any more. |
28757baa |
3001 | |
0078ec44 |
3002 | You need something much more random than the default seed for |
3003 | cryptographic purposes, though. Checksumming the compressed output of |
3004 | one or more rapidly changing operating system status programs is the |
3005 | usual method. For example: |
28757baa |
3006 | |
3007 | srand (time ^ $$ ^ unpack "%L*", `ps axww | gzip`); |
3008 | |
0078ec44 |
3009 | If you're particularly concerned with this, see the Math::TrulyRandom |
3010 | module in CPAN. |
3011 | |
3012 | Do I<not> call srand() multiple times in your program unless you know |
28757baa |
3013 | exactly what you're doing and why you're doing it. The point of the |
3014 | function is to "seed" the rand() function so that rand() can produce |
3015 | a different sequence each time you run your program. Just do it once at the |
3016 | top of your program, or you I<won't> get random numbers out of rand()! |
3017 | |
3018 | Frequently called programs (like CGI scripts) that simply use |
3019 | |
3020 | time ^ $$ |
3021 | |
3022 | for a seed can fall prey to the mathematical property that |
3023 | |
3024 | a^b == (a+1)^(b+1) |
3025 | |
0078ec44 |
3026 | one-third of the time. So don't do that. |
28757baa |
3027 | |
a0d0e21e |
3028 | =item stat FILEHANDLE |
3029 | |
3030 | =item stat EXPR |
3031 | |
bbce6d69 |
3032 | =item stat |
3033 | |
a0d0e21e |
3034 | Returns a 13-element array giving the status info for a file, either the |
bbce6d69 |
3035 | file opened via FILEHANDLE, or named by EXPR. If EXPR is omitted, it |
3036 | stats $_. Returns a null list if the stat fails. Typically used as |
3037 | follows: |
3038 | |
a0d0e21e |
3039 | |
3040 | ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size, |
3041 | $atime,$mtime,$ctime,$blksize,$blocks) |
3042 | = stat($filename); |
3043 | |
c07a80fd |
3044 | Not all fields are supported on all filesystem types. Here are the |
3045 | meaning of the fields: |
3046 | |
3047 | dev device number of filesystem |
3048 | ino inode number |
3049 | mode file mode (type and permissions) |
3050 | nlink number of (hard) links to the file |
3051 | uid numeric user ID of file's owner |
5f05dabc |
3052 | gid numeric group ID of file's owner |
c07a80fd |
3053 | rdev the device identifier (special files only) |
3054 | size total size of file, in bytes |
3055 | atime last access time since the epoch |
3056 | mtime last modify time since the epoch |
3057 | ctime inode change time (NOT creation type!) since the epoch |
5f05dabc |
3058 | blksize preferred block size for file system I/O |
c07a80fd |
3059 | blocks actual number of blocks allocated |
3060 | |
3061 | (The epoch was at 00:00 January 1, 1970 GMT.) |
3062 | |
a0d0e21e |
3063 | If stat is passed the special filehandle consisting of an underline, no |
3064 | stat is done, but the current contents of the stat structure from the |
3065 | last stat or filetest are returned. Example: |
3066 | |
3067 | if (-x $file && (($d) = stat(_)) && $d < 0) { |
3068 | print "$file is executable NFS file\n"; |
3069 | } |
3070 | |
5f05dabc |
3071 | (This works on machines only for which the device number is negative under NFS.) |
a0d0e21e |
3072 | |
3073 | =item study SCALAR |
3074 | |
3075 | =item study |
3076 | |
184e9718 |
3077 | Takes extra time to study SCALAR (C<$_> if unspecified) in anticipation of |
a0d0e21e |
3078 | doing many pattern matches on the string before it is next modified. |
3079 | This may or may not save time, depending on the nature and number of |
3080 | patterns you are searching on, and on the distribution of character |
3081 | frequencies in the string to be searched--you probably want to compare |
5f05dabc |
3082 | run times with and without it to see which runs faster. Those loops |
a0d0e21e |
3083 | which scan for many short constant strings (including the constant |
3084 | parts of more complex patterns) will benefit most. You may have only |
3085 | one study active at a time--if you study a different scalar the first |
3086 | is "unstudied". (The way study works is this: a linked list of every |
3087 | character in the string to be searched is made, so we know, for |
3088 | example, where all the 'k' characters are. From each search string, |
3089 | the rarest character is selected, based on some static frequency tables |
3090 | constructed from some C programs and English text. Only those places |
3091 | that contain this "rarest" character are examined.) |
3092 | |
3093 | For example, here is a loop which inserts index producing entries |
3094 | before any line containing a certain pattern: |
3095 | |
3096 | while (<>) { |
3097 | study; |
3098 | print ".IX foo\n" if /\bfoo\b/; |
3099 | print ".IX bar\n" if /\bbar\b/; |
3100 | print ".IX blurfl\n" if /\bblurfl\b/; |
3101 | ... |
3102 | print; |
3103 | } |
3104 | |
3105 | In searching for /\bfoo\b/, only those locations in $_ that contain "f" |
3106 | will be looked at, because "f" is rarer than "o". In general, this is |
3107 | a big win except in pathological cases. The only question is whether |
3108 | it saves you more time than it took to build the linked list in the |
3109 | first place. |
3110 | |
3111 | Note that if you have to look for strings that you don't know till |
3112 | runtime, you can build an entire loop as a string and eval that to |
3113 | avoid recompiling all your patterns all the time. Together with |
3114 | undefining $/ to input entire files as one record, this can be very |
3115 | fast, often faster than specialized programs like fgrep(1). The following |
184e9718 |
3116 | scans a list of files (C<@files>) for a list of words (C<@words>), and prints |
a0d0e21e |
3117 | out the names of those files that contain a match: |
3118 | |
3119 | $search = 'while (<>) { study;'; |
3120 | foreach $word (@words) { |
3121 | $search .= "++\$seen{\$ARGV} if /\\b$word\\b/;\n"; |
3122 | } |
3123 | $search .= "}"; |
3124 | @ARGV = @files; |
3125 | undef $/; |
3126 | eval $search; # this screams |
5f05dabc |
3127 | $/ = "\n"; # put back to normal input delimiter |
a0d0e21e |
3128 | foreach $file (sort keys(%seen)) { |
3129 | print $file, "\n"; |
3130 | } |
3131 | |
cb1a09d0 |
3132 | =item sub BLOCK |
3133 | |
3134 | =item sub NAME |
3135 | |
3136 | =item sub NAME BLOCK |
3137 | |
3138 | This is subroutine definition, not a real function I<per se>. With just a |
3139 | NAME (and possibly prototypes), it's just a forward declaration. Without |
3140 | a NAME, it's an anonymous function declaration, and does actually return a |
3141 | value: the CODE ref of the closure you just created. See L<perlsub> and |
3142 | L<perlref> for details. |
3143 | |
a0d0e21e |
3144 | =item substr EXPR,OFFSET,LEN |
3145 | |
3146 | =item substr EXPR,OFFSET |
3147 | |
3148 | Extracts a substring out of EXPR and returns it. First character is at |
3149 | offset 0, or whatever you've set $[ to. If OFFSET is negative, starts |
3150 | that far from the end of the string. If LEN is omitted, returns |
748a9306 |
3151 | everything to the end of the string. If LEN is negative, leaves that |
3152 | many characters off the end of the string. |
3153 | |
3154 | You can use the substr() function |
a0d0e21e |
3155 | as an lvalue, in which case EXPR must be an lvalue. If you assign |
3156 | something shorter than LEN, the string will shrink, and if you assign |
3157 | something longer than LEN, the string will grow to accommodate it. To |
3158 | keep the string the same length you may need to pad or chop your value |
3159 | using sprintf(). |
3160 | |
3161 | =item symlink OLDFILE,NEWFILE |
3162 | |
3163 | Creates a new filename symbolically linked to the old filename. |
3164 | Returns 1 for success, 0 otherwise. On systems that don't support |
3165 | symbolic links, produces a fatal error at run time. To check for that, |
3166 | use eval: |
3167 | |
3168 | $symlink_exists = (eval 'symlink("","");', $@ eq ''); |
3169 | |
3170 | =item syscall LIST |
3171 | |
3172 | Calls the system call specified as the first element of the list, |
3173 | passing the remaining elements as arguments to the system call. If |
3174 | unimplemented, produces a fatal error. The arguments are interpreted |
3175 | as follows: if a given argument is numeric, the argument is passed as |
3176 | an int. If not, the pointer to the string value is passed. You are |
3177 | responsible to make sure a string is pre-extended long enough to |
3178 | receive any result that might be written into a string. If your |
3179 | integer arguments are not literals and have never been interpreted in a |
3180 | numeric context, you may need to add 0 to them to force them to look |
3181 | like numbers. |
3182 | |
3183 | require 'syscall.ph'; # may need to run h2ph |
3184 | syscall(&SYS_write, fileno(STDOUT), "hi there\n", 9); |
3185 | |
5f05dabc |
3186 | Note that Perl supports passing of up to only 14 arguments to your system call, |
a0d0e21e |
3187 | which in practice should usually suffice. |
3188 | |
c07a80fd |
3189 | =item sysopen FILEHANDLE,FILENAME,MODE |
3190 | |
3191 | =item sysopen FILEHANDLE,FILENAME,MODE,PERMS |
3192 | |
3193 | Opens the file whose filename is given by FILENAME, and associates it |
3194 | with FILEHANDLE. If FILEHANDLE is an expression, its value is used as |
3195 | the name of the real filehandle wanted. This function calls the |
3196 | underlying operating system's C<open> function with the parameters |
3197 | FILENAME, MODE, PERMS. |
3198 | |
3199 | The possible values and flag bits of the MODE parameter are |
3200 | system-dependent; they are available via the standard module C<Fcntl>. |
3201 | However, for historical reasons, some values are universal: zero means |
3202 | read-only, one means write-only, and two means read/write. |
3203 | |
3204 | If the file named by FILENAME does not exist and the C<open> call |
3205 | creates it (typically because MODE includes the O_CREAT flag), then |
3206 | the value of PERMS specifies the permissions of the newly created |
3207 | file. If PERMS is omitted, the default value is 0666, which allows |
3208 | read and write for all. This default is reasonable: see C<umask>. |
3209 | |
28757baa |
3210 | The IO::File module provides a more object-oriented approach, if you're |
3211 | into that kind of thing. |
3212 | |
a0d0e21e |
3213 | =item sysread FILEHANDLE,SCALAR,LENGTH,OFFSET |
3214 | |
3215 | =item sysread FILEHANDLE,SCALAR,LENGTH |
3216 | |
3217 | Attempts to read LENGTH bytes of data into variable SCALAR from the |
3218 | specified FILEHANDLE, using the system call read(2). It bypasses |
3219 | stdio, so mixing this with other kinds of reads may cause confusion. |
3220 | Returns the number of bytes actually read, or undef if there was an |
ff68c719 |
3221 | error. SCALAR will be grown or shrunk so that the last byte actually |
3222 | read is the last byte of the scalar after the read. |
3223 | |
3224 | An OFFSET may be specified to place the read data at some place in the |
3225 | string other than the beginning. A negative OFFSET specifies |
3226 | placement at that many bytes counting backwards from the end of the |
3227 | string. A positive OFFSET greater than the length of SCALAR results |
3228 | in the string being padded to the required size with "\0" bytes before |
3229 | the result of the read is appended. |
a0d0e21e |
3230 | |
3231 | =item system LIST |
3232 | |
3233 | Does exactly the same thing as "exec LIST" except that a fork is done |
3234 | first, and the parent process waits for the child process to complete. |
3235 | Note that argument processing varies depending on the number of |
3236 | arguments. The return value is the exit status of the program as |
3237 | returned by the wait() call. To get the actual exit value divide by |
cb1a09d0 |
3238 | 256. See also L</exec>. This is I<NOT> what you want to use to capture |
28757baa |
3239 | the output from a command, for that you should use merely back-ticks or |
3240 | qx//, as described in L<perlop/"`STRING`">. |
a0d0e21e |
3241 | |
28757baa |
3242 | Because system() and back-ticks block SIGINT and SIGQUIT, killing the |
3243 | program they're running doesn't actually interrupt your program. |
3244 | |
3245 | @args = ("command", "arg1", "arg2"); |
3246 | system(@args) == 0 |
3247 | or die "system @args failed: $?" |
3248 | |
3249 | Here's a more elaborate example of analysing the return value from |
3250 | system() on a UNIX system to check for all possibilities, including for |
3251 | signals and coredumps. |
3252 | |
3253 | $rc = 0xffff & system @args; |
3254 | printf "system(%s) returned %#04x: ", "@args", $rc; |
3255 | if ($rc == 0) { |
3256 | print "ran with normal exit\n"; |
3257 | } |
3258 | elsif ($rc == 0xff00) { |
3259 | print "command failed: $!\n"; |
3260 | } |
3261 | elsif ($rc > 0x80) { |
3262 | $rc >>= 8; |
3263 | print "ran with non-zero exit status $rc\n"; |
3264 | } |
3265 | else { |
3266 | print "ran with "; |
3267 | if ($rc & 0x80) { |
3268 | $rc &= ~0x80; |
3269 | print "coredump from "; |
3270 | } |
3271 | print "signal $rc\n" |
3272 | } |
3273 | $ok = ($rc != 0); |
3274 | |
a0d0e21e |
3275 | =item syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET |
3276 | |
3277 | =item syswrite FILEHANDLE,SCALAR,LENGTH |
3278 | |
3279 | Attempts to write LENGTH bytes of data from variable SCALAR to the |
3280 | specified FILEHANDLE, using the system call write(2). It bypasses |
3281 | stdio, so mixing this with prints may cause confusion. Returns the |
bbce6d69 |
3282 | number of bytes actually written, or undef if there was an error. |
3283 | If the length is greater than the available data, only as much data as |
ff68c719 |
3284 | is available will be written. |
3285 | |
3286 | An OFFSET may be specified to write the data from some part of the |
3287 | string other than the beginning. A negative OFFSET specifies writing |
3288 | from that many bytes counting backwards from the end of the string. |
a0d0e21e |
3289 | |
3290 | =item tell FILEHANDLE |
3291 | |
3292 | =item tell |
3293 | |
3294 | Returns the current file position for FILEHANDLE. FILEHANDLE may be an |
3295 | expression whose value gives the name of the actual filehandle. If |
3296 | FILEHANDLE is omitted, assumes the file last read. |
3297 | |
3298 | =item telldir DIRHANDLE |
3299 | |
3300 | Returns the current position of the readdir() routines on DIRHANDLE. |
3301 | Value may be given to seekdir() to access a particular location in a |
3302 | directory. Has the same caveats about possible directory compaction as |
3303 | the corresponding system library routine. |
3304 | |
4633a7c4 |
3305 | =item tie VARIABLE,CLASSNAME,LIST |
a0d0e21e |
3306 | |
4633a7c4 |
3307 | This function binds a variable to a package class that will provide the |
3308 | implementation for the variable. VARIABLE is the name of the variable |
3309 | to be enchanted. CLASSNAME is the name of a class implementing objects |
3310 | of correct type. Any additional arguments are passed to the "new" |
3311 | method of the class (meaning TIESCALAR, TIEARRAY, or TIEHASH). |
3312 | Typically these are arguments such as might be passed to the dbm_open() |
cb1a09d0 |
3313 | function of C. The object returned by the "new" method is also |
3314 | returned by the tie() function, which would be useful if you want to |
4633a7c4 |
3315 | access other methods in CLASSNAME. |
a0d0e21e |
3316 | |
3317 | Note that functions such as keys() and values() may return huge array |
748a9306 |
3318 | values when used on large objects, like DBM files. You may prefer to |
3319 | use the each() function to iterate over such. Example: |
a0d0e21e |
3320 | |
3321 | # print out history file offsets |
4633a7c4 |
3322 | use NDBM_File; |
da0045b7 |
3323 | tie(%HIST, 'NDBM_File', '/usr/lib/news/history', 1, 0); |
a0d0e21e |
3324 | while (($key,$val) = each %HIST) { |
3325 | print $key, ' = ', unpack('L',$val), "\n"; |
3326 | } |
3327 | untie(%HIST); |
3328 | |
4633a7c4 |
3329 | A class implementing an associative array should have the following |
a0d0e21e |
3330 | methods: |
3331 | |
4633a7c4 |
3332 | TIEHASH classname, LIST |
a0d0e21e |
3333 | DESTROY this |
3334 | FETCH this, key |
3335 | STORE this, key, value |
3336 | DELETE this, key |
3337 | EXISTS this, key |
3338 | FIRSTKEY this |
3339 | NEXTKEY this, lastkey |
3340 | |
4633a7c4 |
3341 | A class implementing an ordinary array should have the following methods: |
a0d0e21e |
3342 | |
4633a7c4 |
3343 | TIEARRAY classname, LIST |
a0d0e21e |
3344 | DESTROY this |
3345 | FETCH this, key |
3346 | STORE this, key, value |
3347 | [others TBD] |
3348 | |
4633a7c4 |
3349 | A class implementing a scalar should have the following methods: |
a0d0e21e |
3350 | |
4633a7c4 |
3351 | TIESCALAR classname, LIST |
a0d0e21e |
3352 | DESTROY this |
3353 | FETCH this, |
3354 | STORE this, value |
3355 | |
4633a7c4 |
3356 | Unlike dbmopen(), the tie() function will not use or require a module |
3357 | for you--you need to do that explicitly yourself. See L<DB_File> |
3358 | or the F<Config> module for interesting tie() implementations. |
3359 | |
f3cbc334 |
3360 | =item tied VARIABLE |
3361 | |
3362 | Returns a reference to the object underlying VARIABLE (the same value |
3363 | that was originally returned by the tie() call which bound the variable |
3364 | to a package.) Returns the undefined value if VARIABLE isn't tied to a |
3365 | package. |
3366 | |
a0d0e21e |
3367 | =item time |
3368 | |
da0045b7 |
3369 | Returns the number of non-leap seconds since whatever time the system |
3370 | considers to be the epoch (that's 00:00:00, January 1, 1904 for MacOS, |
3371 | and 00:00:00 UTC, January 1, 1970 for most other systems). |
3372 | Suitable for feeding to gmtime() and localtime(). |
a0d0e21e |
3373 | |
3374 | =item times |
3375 | |
3376 | Returns a four-element array giving the user and system times, in |
3377 | seconds, for this process and the children of this process. |
3378 | |
3379 | ($user,$system,$cuser,$csystem) = times; |
3380 | |
3381 | =item tr/// |
3382 | |
3383 | The translation operator. See L<perlop>. |
3384 | |
3385 | =item truncate FILEHANDLE,LENGTH |
3386 | |
3387 | =item truncate EXPR,LENGTH |
3388 | |
3389 | Truncates the file opened on FILEHANDLE, or named by EXPR, to the |
3390 | specified length. Produces a fatal error if truncate isn't implemented |
3391 | on your system. |
3392 | |
3393 | =item uc EXPR |
3394 | |
bbce6d69 |
3395 | =item uc |
3396 | |
a0d0e21e |
3397 | Returns an uppercased version of EXPR. This is the internal function |
3398 | implementing the \U escape in double-quoted strings. |
a034a98d |
3399 | Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>. |
a0d0e21e |
3400 | |
bbce6d69 |
3401 | If EXPR is omitted, uses $_. |
3402 | |
a0d0e21e |
3403 | =item ucfirst EXPR |
3404 | |
bbce6d69 |
3405 | =item ucfirst |
3406 | |
a0d0e21e |
3407 | Returns the value of EXPR with the first character uppercased. This is |
3408 | the internal function implementing the \u escape in double-quoted strings. |
a034a98d |
3409 | Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>. |
a0d0e21e |
3410 | |
bbce6d69 |
3411 | If EXPR is omitted, uses $_. |
3412 | |
a0d0e21e |
3413 | =item umask EXPR |
3414 | |
3415 | =item umask |
3416 | |
3417 | Sets the umask for the process and returns the old one. If EXPR is |
5f05dabc |
3418 | omitted, returns merely the current umask. |
a0d0e21e |
3419 | |
3420 | =item undef EXPR |
3421 | |
3422 | =item undef |
3423 | |
5f05dabc |
3424 | Undefines the value of EXPR, which must be an lvalue. Use on only a |
a0d0e21e |
3425 | scalar value, an entire array, or a subroutine name (using "&"). (Using undef() |
3426 | will probably not do what you expect on most predefined variables or |
3427 | DBM list values, so don't do that.) Always returns the undefined value. You can omit |
3428 | the EXPR, in which case nothing is undefined, but you still get an |
3429 | undefined value that you could, for instance, return from a |
3430 | subroutine. Examples: |
3431 | |
3432 | undef $foo; |
3433 | undef $bar{'blurfl'}; |
3434 | undef @ary; |
3435 | undef %assoc; |
3436 | undef &mysub; |
3437 | return (wantarray ? () : undef) if $they_blew_it; |
3438 | |
3439 | =item unlink LIST |
3440 | |
bbce6d69 |
3441 | =item unlink |
3442 | |
a0d0e21e |
3443 | Deletes a list of files. Returns the number of files successfully |
3444 | deleted. |
3445 | |
3446 | $cnt = unlink 'a', 'b', 'c'; |
3447 | unlink @goners; |
3448 | unlink <*.bak>; |
3449 | |
3450 | Note: unlink will not delete directories unless you are superuser and |
3451 | the B<-U> flag is supplied to Perl. Even if these conditions are |
3452 | met, be warned that unlinking a directory can inflict damage on your |
3453 | filesystem. Use rmdir instead. |
3454 | |
bbce6d69 |
3455 | If LIST is omitted, uses $_. |
3456 | |
a0d0e21e |
3457 | =item unpack TEMPLATE,EXPR |
3458 | |
3459 | Unpack does the reverse of pack: it takes a string representing a |
3460 | structure and expands it out into a list value, returning the array |
5f05dabc |
3461 | value. (In a scalar context, it returns merely the first value |
a0d0e21e |
3462 | produced.) The TEMPLATE has the same format as in the pack function. |
3463 | Here's a subroutine that does substring: |
3464 | |
3465 | sub substr { |
3466 | local($what,$where,$howmuch) = @_; |
3467 | unpack("x$where a$howmuch", $what); |
3468 | } |
3469 | |
3470 | and then there's |
3471 | |
3472 | sub ordinal { unpack("c",$_[0]); } # same as ord() |
3473 | |
184e9718 |
3474 | In addition, you may prefix a field with a %E<lt>numberE<gt> to indicate that |
3475 | you want a E<lt>numberE<gt>-bit checksum of the items instead of the items |
a0d0e21e |
3476 | themselves. Default is a 16-bit checksum. For example, the following |
3477 | computes the same number as the System V sum program: |
3478 | |
3479 | while (<>) { |
3480 | $checksum += unpack("%16C*", $_); |
3481 | } |
3482 | $checksum %= 65536; |
3483 | |
3484 | The following efficiently counts the number of set bits in a bit vector: |
3485 | |
3486 | $setbits = unpack("%32b*", $selectmask); |
3487 | |
3488 | =item untie VARIABLE |
3489 | |
3490 | Breaks the binding between a variable and a package. (See tie().) |
3491 | |
3492 | =item unshift ARRAY,LIST |
3493 | |
3494 | Does the opposite of a C<shift>. Or the opposite of a C<push>, |
3495 | depending on how you look at it. Prepends list to the front of the |
3496 | array, and returns the new number of elements in the array. |
3497 | |
3498 | unshift(ARGV, '-e') unless $ARGV[0] =~ /^-/; |
3499 | |
3500 | Note the LIST is prepended whole, not one element at a time, so the |
3501 | prepended elements stay in the same order. Use reverse to do the |
3502 | reverse. |
3503 | |
3504 | =item use Module LIST |
3505 | |
3506 | =item use Module |
3507 | |
da0045b7 |
3508 | =item use Module VERSION LIST |
3509 | |
3510 | =item use VERSION |
3511 | |
a0d0e21e |
3512 | Imports some semantics into the current package from the named module, |
3513 | generally by aliasing certain subroutine or variable names into your |
3514 | package. It is exactly equivalent to |
3515 | |
3516 | BEGIN { require Module; import Module LIST; } |
3517 | |
da0045b7 |
3518 | except that Module I<must> be a bare word. |
3519 | |
3520 | If the first argument to C<use> is a number, it is treated as a version |
3521 | number instead of a module name. If the version of the Perl interpreter |
3522 | is less than VERSION, then an error message is printed and Perl exits |
3523 | immediately. This is often useful if you need to check the current |
3524 | Perl version before C<use>ing library modules which have changed in |
3525 | incompatible ways from older versions of Perl. (We try not to do |
3526 | this more than we have to.) |
3527 | |
a0d0e21e |
3528 | The BEGIN forces the require and import to happen at compile time. The |
3529 | require makes sure the module is loaded into memory if it hasn't been |
3530 | yet. The import is not a builtin--it's just an ordinary static method |
3531 | call into the "Module" package to tell the module to import the list of |
3532 | features back into the current package. The module can implement its |
3533 | import method any way it likes, though most modules just choose to |
3534 | derive their import method via inheritance from the Exporter class that |
55497cff |
3535 | is defined in the Exporter module. See L<Exporter>. If no import |
3536 | method can be found then the error is currently silently ignored. This |
3537 | may change to a fatal error in a future version. |
cb1a09d0 |
3538 | |
3539 | If you don't want your namespace altered, explicitly supply an empty list: |
3540 | |
3541 | use Module (); |
3542 | |
3543 | That is exactly equivalent to |
3544 | |
3545 | BEGIN { require Module; } |
a0d0e21e |
3546 | |
da0045b7 |
3547 | If the VERSION argument is present between Module and LIST, then the |
71be2cbc |
3548 | C<use> will call the VERSION method in class Module with the given |
3549 | version as an argument. The default VERSION method, inherited from |
3550 | the Universal class, croaks if the given version is larger than the |
3551 | value of the variable $Module::VERSION. (Note that there is not a |
3552 | comma after VERSION!) |
da0045b7 |
3553 | |
a0d0e21e |
3554 | Because this is a wide-open interface, pragmas (compiler directives) |
3555 | are also implemented this way. Currently implemented pragmas are: |
3556 | |
3557 | use integer; |
4633a7c4 |
3558 | use diagnostics; |
a0d0e21e |
3559 | use sigtrap qw(SEGV BUS); |
3560 | use strict qw(subs vars refs); |
3561 | use subs qw(afunc blurfl); |
3562 | |
5f05dabc |
3563 | These pseudo-modules import semantics into the current block scope, unlike |
a0d0e21e |
3564 | ordinary modules, which import symbols into the current package (which are |
3565 | effective through the end of the file). |
3566 | |
3567 | There's a corresponding "no" command that unimports meanings imported |
5f05dabc |
3568 | by use, i.e., it calls C<unimport Module LIST> instead of C<import>. |
a0d0e21e |
3569 | |
3570 | no integer; |
3571 | no strict 'refs'; |
3572 | |
55497cff |
3573 | If no unimport method can be found the call fails with a fatal error. |
3574 | |
a0d0e21e |
3575 | See L<perlmod> for a list of standard modules and pragmas. |
3576 | |
3577 | =item utime LIST |
3578 | |
3579 | Changes the access and modification times on each file of a list of |
3580 | files. The first two elements of the list must be the NUMERICAL access |
3581 | and modification times, in that order. Returns the number of files |
3582 | successfully changed. The inode modification time of each file is set |
3583 | to the current time. Example of a "touch" command: |
3584 | |
3585 | #!/usr/bin/perl |
3586 | $now = time; |
3587 | utime $now, $now, @ARGV; |
3588 | |
3589 | =item values ASSOC_ARRAY |
3590 | |
3591 | Returns a normal array consisting of all the values of the named |
3592 | associative array. (In a scalar context, returns the number of |
3593 | values.) The values are returned in an apparently random order, but it |
3594 | is the same order as either the keys() or each() function would produce |
c07a80fd |
3595 | on the same array. See also keys(), each(), and sort(). |
a0d0e21e |
3596 | |
3597 | =item vec EXPR,OFFSET,BITS |
3598 | |
22dc801b |
3599 | Treats the string in EXPR as a vector of unsigned integers, and |
5f05dabc |
3600 | returns the value of the bit field specified by OFFSET. BITS specifies |
22dc801b |
3601 | the number of bits that are reserved for each entry in the bit |
3602 | vector. This must be a power of two from 1 to 32. vec() may also be |
5f05dabc |
3603 | assigned to, in which case parentheses are needed to give the expression |
22dc801b |
3604 | the correct precedence as in |
3605 | |
3606 | vec($image, $max_x * $x + $y, 8) = 3; |
a0d0e21e |
3607 | |
3608 | Vectors created with vec() can also be manipulated with the logical |
5f05dabc |
3609 | operators |, &, and ^, which will assume a bit vector operation is |
a0d0e21e |
3610 | desired when both operands are strings. |
3611 | |
3612 | To transform a bit vector into a string or array of 0's and 1's, use these: |
3613 | |
3614 | $bits = unpack("b*", $vector); |
3615 | @bits = split(//, unpack("b*", $vector)); |
3616 | |
3617 | If you know the exact length in bits, it can be used in place of the *. |
3618 | |
3619 | =item wait |
3620 | |
3621 | Waits for a child process to terminate and returns the pid of the |
3622 | deceased process, or -1 if there are no child processes. The status is |
184e9718 |
3623 | returned in C<$?>. |
a0d0e21e |
3624 | |
3625 | =item waitpid PID,FLAGS |
3626 | |
3627 | Waits for a particular child process to terminate and returns the pid |
3628 | of the deceased process, or -1 if there is no such child process. The |
184e9718 |
3629 | status is returned in C<$?>. If you say |
a0d0e21e |
3630 | |
5f05dabc |
3631 | use POSIX ":sys_wait_h"; |
a0d0e21e |
3632 | ... |
3633 | waitpid(-1,&WNOHANG); |
3634 | |
3635 | then you can do a non-blocking wait for any process. Non-blocking wait |
5f05dabc |
3636 | is available on machines supporting either the waitpid(2) or |
a0d0e21e |
3637 | wait4(2) system calls. However, waiting for a particular pid with |
3638 | FLAGS of 0 is implemented everywhere. (Perl emulates the system call |
3639 | by remembering the status values of processes that have exited but have |
3640 | not been harvested by the Perl script yet.) |
3641 | |
3642 | =item wantarray |
3643 | |
3644 | Returns TRUE if the context of the currently executing subroutine is |
3645 | looking for a list value. Returns FALSE if the context is looking |
3646 | for a scalar. |
3647 | |
3648 | return wantarray ? () : undef; |
3649 | |
3650 | =item warn LIST |
3651 | |
3652 | Produces a message on STDERR just like die(), but doesn't exit or |
4633a7c4 |
3653 | on an exception. |
a0d0e21e |
3654 | |
3655 | =item write FILEHANDLE |
3656 | |
3657 | =item write EXPR |
3658 | |
3659 | =item write |
3660 | |
3661 | Writes a formatted record (possibly multi-line) to the specified file, |
3662 | using the format associated with that file. By default the format for |
3663 | a file is the one having the same name is the filehandle, but the |
3664 | format for the current output channel (see the select() function) may be set |
184e9718 |
3665 | explicitly by assigning the name of the format to the C<$~> variable. |
a0d0e21e |
3666 | |
3667 | Top of form processing is handled automatically: if there is |
3668 | insufficient room on the current page for the formatted record, the |
3669 | page is advanced by writing a form feed, a special top-of-page format |
3670 | is used to format the new page header, and then the record is written. |
3671 | By default the top-of-page format is the name of the filehandle with |
3672 | "_TOP" appended, but it may be dynamically set to the format of your |
184e9718 |
3673 | choice by assigning the name to the C<$^> variable while the filehandle is |
a0d0e21e |
3674 | selected. The number of lines remaining on the current page is in |
184e9718 |
3675 | variable C<$->, which can be set to 0 to force a new page. |
a0d0e21e |
3676 | |
3677 | If FILEHANDLE is unspecified, output goes to the current default output |
3678 | channel, which starts out as STDOUT but may be changed by the |
3679 | C<select> operator. If the FILEHANDLE is an EXPR, then the expression |
3680 | is evaluated and the resulting string is used to look up the name of |
3681 | the FILEHANDLE at run time. For more on formats, see L<perlform>. |
3682 | |
3683 | Note that write is I<NOT> the opposite of read. Unfortunately. |
3684 | |
3685 | =item y/// |
3686 | |
37798a01 |
3687 | The translation operator. See L<perlop>. |
a0d0e21e |
3688 | |
3689 | =back |