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1 | =head1 NAME |
2 | |
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3 | perlfaq5 - Files and Formats ($Revision: 1.12 $, $Date: 2002/03/11 22:25:25 $) |
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4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | This section deals with I/O and the "f" issues: filehandles, flushing, |
8 | formats, and footers. |
9 | |
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10 | =head2 How do I flush/unbuffer an output filehandle? Why must I do this? |
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11 | |
12 | The C standard I/O library (stdio) normally buffers characters sent to |
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13 | devices. This is done for efficiency reasons so that there isn't a |
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14 | system call for each byte. Any time you use print() or write() in |
15 | Perl, you go though this buffering. syswrite() circumvents stdio and |
16 | buffering. |
17 | |
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18 | In most stdio implementations, the type of output buffering and the size of |
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19 | the buffer varies according to the type of device. Disk files are block |
20 | buffered, often with a buffer size of more than 2k. Pipes and sockets |
21 | are often buffered with a buffer size between 1/2 and 2k. Serial devices |
22 | (e.g. modems, terminals) are normally line-buffered, and stdio sends |
23 | the entire line when it gets the newline. |
24 | |
25 | Perl does not support truly unbuffered output (except insofar as you can |
26 | C<syswrite(OUT, $char, 1)>). What it does instead support is "command |
27 | buffering", in which a physical write is performed after every output |
28 | command. This isn't as hard on your system as unbuffering, but does |
29 | get the output where you want it when you want it. |
30 | |
31 | If you expect characters to get to your device when you print them there, |
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32 | you'll want to autoflush its handle. |
33 | Use select() and the C<$|> variable to control autoflushing |
34 | (see L<perlvar/$|> and L<perlfunc/select>): |
35 | |
36 | $old_fh = select(OUTPUT_HANDLE); |
37 | $| = 1; |
38 | select($old_fh); |
39 | |
40 | Or using the traditional idiom: |
41 | |
42 | select((select(OUTPUT_HANDLE), $| = 1)[0]); |
43 | |
44 | Or if don't mind slowly loading several thousand lines of module code |
45 | just because you're afraid of the C<$|> variable: |
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46 | |
47 | use FileHandle; |
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48 | open(DEV, "+</dev/tty"); # ceci n'est pas une pipe |
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49 | DEV->autoflush(1); |
50 | |
51 | or the newer IO::* modules: |
52 | |
53 | use IO::Handle; |
54 | open(DEV, ">/dev/printer"); # but is this? |
55 | DEV->autoflush(1); |
56 | |
57 | or even this: |
58 | |
59 | use IO::Socket; # this one is kinda a pipe? |
60 | $sock = IO::Socket::INET->new(PeerAddr => 'www.perl.com', |
61 | PeerPort => 'http(80)', |
62 | Proto => 'tcp'); |
63 | die "$!" unless $sock; |
64 | |
65 | $sock->autoflush(); |
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66 | print $sock "GET / HTTP/1.0" . "\015\012" x 2; |
67 | $document = join('', <$sock>); |
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68 | print "DOC IS: $document\n"; |
69 | |
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70 | Note the bizarrely hard coded carriage return and newline in their octal |
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71 | equivalents. This is the ONLY way (currently) to assure a proper flush |
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72 | on all platforms, including Macintosh. That's the way things work in |
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73 | network programming: you really should specify the exact bit pattern |
74 | on the network line terminator. In practice, C<"\n\n"> often works, |
75 | but this is not portable. |
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76 | |
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77 | See L<perlfaq9> for other examples of fetching URLs over the web. |
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78 | |
79 | =head2 How do I change one line in a file/delete a line in a file/insert a line in the middle of a file/append to the beginning of a file? |
80 | |
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81 | Use the Tie::File module, which is included in the standard |
82 | distribution since Perl 5.8.0. |
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83 | |
84 | =head2 How do I count the number of lines in a file? |
85 | |
86 | One fairly efficient way is to count newlines in the file. The |
87 | following program uses a feature of tr///, as documented in L<perlop>. |
88 | If your text file doesn't end with a newline, then it's not really a |
89 | proper text file, so this may report one fewer line than you expect. |
90 | |
91 | $lines = 0; |
92 | open(FILE, $filename) or die "Can't open `$filename': $!"; |
93 | while (sysread FILE, $buffer, 4096) { |
94 | $lines += ($buffer =~ tr/\n//); |
95 | } |
96 | close FILE; |
97 | |
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98 | This assumes no funny games with newline translations. |
99 | |
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100 | =head2 How do I make a temporary file name? |
101 | |
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102 | Use the File::Temp module, see L<File::Temp> for more information. |
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103 | |
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104 | use File::Temp qw/ tempfile tempdir /; |
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105 | |
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106 | $dir = tempdir( CLEANUP => 1 ); |
107 | ($fh, $filename) = tempfile( DIR => $dir ); |
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108 | |
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109 | # or if you don't need to know the filename |
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110 | |
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111 | $fh = tempfile( DIR => $dir ); |
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112 | |
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113 | The File::Temp has been a standard module since Perl 5.6.1. If you |
114 | don't have a modern enough Perl installed, use the C<new_tmpfile> |
115 | class method from the IO::File module to get a filehandle opened for |
116 | reading and writing. Use it if you don't need to know the file's name: |
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117 | |
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118 | use IO::File; |
119 | $fh = IO::File->new_tmpfile() |
120 | or die "Unable to make new temporary file: $!"; |
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121 | |
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122 | If you're committed to creating a temporary file by hand, use the |
123 | process ID and/or the current time-value. If you need to have many |
124 | temporary files in one process, use a counter: |
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125 | |
126 | BEGIN { |
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127 | use Fcntl; |
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128 | my $temp_dir = -d '/tmp' ? '/tmp' : $ENV{TMPDIR} || $ENV{TEMP}; |
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129 | my $base_name = sprintf("%s/%d-%d-0000", $temp_dir, $$, time()); |
130 | sub temp_file { |
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131 | local *FH; |
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132 | my $count = 0; |
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133 | until (defined(fileno(FH)) || $count++ > 100) { |
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134 | $base_name =~ s/-(\d+)$/"-" . (1 + $1)/e; |
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135 | sysopen(FH, $base_name, O_WRONLY|O_EXCL|O_CREAT); |
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136 | } |
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137 | if (defined(fileno(FH)) |
138 | return (*FH, $base_name); |
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139 | } else { |
140 | return (); |
141 | } |
142 | } |
143 | } |
144 | |
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145 | =head2 How can I manipulate fixed-record-length files? |
146 | |
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147 | The most efficient way is using pack() and unpack(). This is faster than |
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148 | using substr() when taking many, many strings. It is slower for just a few. |
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149 | |
150 | Here is a sample chunk of code to break up and put back together again |
151 | some fixed-format input lines, in this case from the output of a normal, |
152 | Berkeley-style ps: |
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153 | |
154 | # sample input line: |
155 | # 15158 p5 T 0:00 perl /home/tchrist/scripts/now-what |
156 | $PS_T = 'A6 A4 A7 A5 A*'; |
157 | open(PS, "ps|"); |
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158 | print scalar <PS>; |
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159 | while (<PS>) { |
160 | ($pid, $tt, $stat, $time, $command) = unpack($PS_T, $_); |
161 | for $var (qw!pid tt stat time command!) { |
162 | print "$var: <$$var>\n"; |
163 | } |
164 | print 'line=', pack($PS_T, $pid, $tt, $stat, $time, $command), |
165 | "\n"; |
166 | } |
167 | |
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168 | We've used C<$$var> in a way that forbidden by C<use strict 'refs'>. |
169 | That is, we've promoted a string to a scalar variable reference using |
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170 | symbolic references. This is okay in small programs, but doesn't scale |
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171 | well. It also only works on global variables, not lexicals. |
172 | |
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173 | =head2 How can I make a filehandle local to a subroutine? How do I pass filehandles between subroutines? How do I make an array of filehandles? |
174 | |
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175 | The fastest, simplest, and most direct way is to localize the typeglob |
176 | of the filehandle in question: |
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177 | |
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178 | local *TmpHandle; |
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179 | |
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180 | Typeglobs are fast (especially compared with the alternatives) and |
181 | reasonably easy to use, but they also have one subtle drawback. If you |
182 | had, for example, a function named TmpHandle(), or a variable named |
183 | %TmpHandle, you just hid it from yourself. |
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184 | |
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185 | sub findme { |
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186 | local *HostFile; |
187 | open(HostFile, "</etc/hosts") or die "no /etc/hosts: $!"; |
188 | local $_; # <- VERY IMPORTANT |
189 | while (<HostFile>) { |
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190 | print if /\b127\.(0\.0\.)?1\b/; |
191 | } |
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192 | # *HostFile automatically closes/disappears here |
193 | } |
194 | |
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195 | Here's how to use typeglobs in a loop to open and store a bunch of |
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196 | filehandles. We'll use as values of the hash an ordered |
197 | pair to make it easy to sort the hash in insertion order. |
198 | |
199 | @names = qw(motd termcap passwd hosts); |
200 | my $i = 0; |
201 | foreach $filename (@names) { |
202 | local *FH; |
203 | open(FH, "/etc/$filename") || die "$filename: $!"; |
204 | $file{$filename} = [ $i++, *FH ]; |
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205 | } |
206 | |
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207 | # Using the filehandles in the array |
208 | foreach $name (sort { $file{$a}[0] <=> $file{$b}[0] } keys %file) { |
209 | my $fh = $file{$name}[1]; |
210 | my $line = <$fh>; |
211 | print "$name $. $line"; |
212 | } |
213 | |
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214 | For passing filehandles to functions, the easiest way is to |
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215 | preface them with a star, as in func(*STDIN). |
216 | See L<perlfaq7/"Passing Filehandles"> for details. |
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217 | |
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218 | If you want to create many anonymous handles, you should check out the |
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219 | Symbol, FileHandle, or IO::Handle (etc.) modules. Here's the equivalent |
220 | code with Symbol::gensym, which is reasonably light-weight: |
221 | |
222 | foreach $filename (@names) { |
223 | use Symbol; |
224 | my $fh = gensym(); |
225 | open($fh, "/etc/$filename") || die "open /etc/$filename: $!"; |
226 | $file{$filename} = [ $i++, $fh ]; |
227 | } |
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228 | |
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229 | Here's using the semi-object-oriented FileHandle module, which certainly |
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230 | isn't light-weight: |
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231 | |
232 | use FileHandle; |
233 | |
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234 | foreach $filename (@names) { |
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235 | my $fh = FileHandle->new("/etc/$filename") or die "$filename: $!"; |
236 | $file{$filename} = [ $i++, $fh ]; |
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237 | } |
238 | |
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239 | Please understand that whether the filehandle happens to be a (probably |
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240 | localized) typeglob or an anonymous handle from one of the modules |
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241 | in no way affects the bizarre rules for managing indirect handles. |
242 | See the next question. |
243 | |
244 | =head2 How can I use a filehandle indirectly? |
245 | |
246 | An indirect filehandle is using something other than a symbol |
247 | in a place that a filehandle is expected. Here are ways |
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248 | to get indirect filehandles: |
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249 | |
250 | $fh = SOME_FH; # bareword is strict-subs hostile |
251 | $fh = "SOME_FH"; # strict-refs hostile; same package only |
252 | $fh = *SOME_FH; # typeglob |
253 | $fh = \*SOME_FH; # ref to typeglob (bless-able) |
254 | $fh = *SOME_FH{IO}; # blessed IO::Handle from *SOME_FH typeglob |
255 | |
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256 | Or, you can use the C<new> method from the FileHandle or IO modules to |
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257 | create an anonymous filehandle, store that in a scalar variable, |
258 | and use it as though it were a normal filehandle. |
259 | |
260 | use FileHandle; |
261 | $fh = FileHandle->new(); |
262 | |
263 | use IO::Handle; # 5.004 or higher |
264 | $fh = IO::Handle->new(); |
265 | |
266 | Then use any of those as you would a normal filehandle. Anywhere that |
267 | Perl is expecting a filehandle, an indirect filehandle may be used |
268 | instead. An indirect filehandle is just a scalar variable that contains |
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269 | a filehandle. Functions like C<print>, C<open>, C<seek>, or |
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270 | the C<< <FH> >> diamond operator will accept either a read filehandle |
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271 | or a scalar variable containing one: |
272 | |
273 | ($ifh, $ofh, $efh) = (*STDIN, *STDOUT, *STDERR); |
274 | print $ofh "Type it: "; |
275 | $got = <$ifh> |
276 | print $efh "What was that: $got"; |
277 | |
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278 | If you're passing a filehandle to a function, you can write |
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279 | the function in two ways: |
280 | |
281 | sub accept_fh { |
282 | my $fh = shift; |
283 | print $fh "Sending to indirect filehandle\n"; |
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284 | } |
285 | |
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286 | Or it can localize a typeglob and use the filehandle directly: |
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287 | |
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288 | sub accept_fh { |
289 | local *FH = shift; |
290 | print FH "Sending to localized filehandle\n"; |
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291 | } |
292 | |
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293 | Both styles work with either objects or typeglobs of real filehandles. |
294 | (They might also work with strings under some circumstances, but this |
295 | is risky.) |
296 | |
297 | accept_fh(*STDOUT); |
298 | accept_fh($handle); |
299 | |
300 | In the examples above, we assigned the filehandle to a scalar variable |
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301 | before using it. That is because only simple scalar variables, not |
302 | expressions or subscripts of hashes or arrays, can be used with |
303 | built-ins like C<print>, C<printf>, or the diamond operator. Using |
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304 | something other than a simple scalar variable as a filehandle is |
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305 | illegal and won't even compile: |
306 | |
307 | @fd = (*STDIN, *STDOUT, *STDERR); |
308 | print $fd[1] "Type it: "; # WRONG |
309 | $got = <$fd[0]> # WRONG |
310 | print $fd[2] "What was that: $got"; # WRONG |
311 | |
312 | With C<print> and C<printf>, you get around this by using a block and |
313 | an expression where you would place the filehandle: |
314 | |
315 | print { $fd[1] } "funny stuff\n"; |
316 | printf { $fd[1] } "Pity the poor %x.\n", 3_735_928_559; |
317 | # Pity the poor deadbeef. |
318 | |
319 | That block is a proper block like any other, so you can put more |
320 | complicated code there. This sends the message out to one of two places: |
321 | |
322 | $ok = -x "/bin/cat"; |
323 | print { $ok ? $fd[1] : $fd[2] } "cat stat $ok\n"; |
324 | print { $fd[ 1+ ($ok || 0) ] } "cat stat $ok\n"; |
325 | |
326 | This approach of treating C<print> and C<printf> like object methods |
327 | calls doesn't work for the diamond operator. That's because it's a |
328 | real operator, not just a function with a comma-less argument. Assuming |
329 | you've been storing typeglobs in your structure as we did above, you |
330 | can use the built-in function named C<readline> to reads a record just |
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331 | as C<< <> >> does. Given the initialization shown above for @fd, this |
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332 | would work, but only because readline() require a typeglob. It doesn't |
333 | work with objects or strings, which might be a bug we haven't fixed yet. |
334 | |
335 | $got = readline($fd[0]); |
336 | |
337 | Let it be noted that the flakiness of indirect filehandles is not |
338 | related to whether they're strings, typeglobs, objects, or anything else. |
339 | It's the syntax of the fundamental operators. Playing the object |
340 | game doesn't help you at all here. |
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341 | |
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342 | =head2 How can I set up a footer format to be used with write()? |
343 | |
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344 | There's no builtin way to do this, but L<perlform> has a couple of |
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345 | techniques to make it possible for the intrepid hacker. |
346 | |
347 | =head2 How can I write() into a string? |
348 | |
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349 | See L<perlform/"Accessing Formatting Internals"> for an swrite() function. |
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350 | |
351 | =head2 How can I output my numbers with commas added? |
352 | |
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353 | This one from Benjamin Goldberg will do it for you: |
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354 | |
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355 | s/(^[-+]?\d+?(?=(?>(?:\d{3})+)(?!\d))|\G\d{3}(?=\d))/$1,/g; |
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356 | |
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357 | or written verbosely: |
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358 | |
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359 | s/( |
360 | ^[-+]? # beginning of number. |
361 | \d{1,3}? # first digits before first comma |
362 | (?= # followed by, (but not included in the match) : |
363 | (?>(?:\d{3})+) # some positive multiple of three digits. |
364 | (?!\d) # an *exact* multiple, not x * 3 + 1 or whatever. |
365 | ) |
366 | | # or: |
367 | \G\d{3} # after the last group, get three digits |
368 | (?=\d) # but they have to have more digits after them. |
369 | )/$1,/xg; |
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370 | |
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371 | =head2 How can I translate tildes (~) in a filename? |
372 | |
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373 | Use the <> (glob()) operator, documented in L<perlfunc>. Older |
374 | versions of Perl require that you have a shell installed that groks |
375 | tildes. Recent perl versions have this feature built in. The |
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376 | File::KGlob module (available from CPAN) gives more portable glob |
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377 | functionality. |
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378 | |
379 | Within Perl, you may use this directly: |
380 | |
381 | $filename =~ s{ |
382 | ^ ~ # find a leading tilde |
383 | ( # save this in $1 |
384 | [^/] # a non-slash character |
385 | * # repeated 0 or more times (0 means me) |
386 | ) |
387 | }{ |
388 | $1 |
389 | ? (getpwnam($1))[7] |
390 | : ( $ENV{HOME} || $ENV{LOGDIR} ) |
391 | }ex; |
392 | |
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393 | =head2 How come when I open a file read-write it wipes it out? |
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394 | |
395 | Because you're using something like this, which truncates the file and |
396 | I<then> gives you read-write access: |
397 | |
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398 | open(FH, "+> /path/name"); # WRONG (almost always) |
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399 | |
400 | Whoops. You should instead use this, which will fail if the file |
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401 | doesn't exist. |
402 | |
403 | open(FH, "+< /path/name"); # open for update |
404 | |
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405 | Using ">" always clobbers or creates. Using "<" never does |
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406 | either. The "+" doesn't change this. |
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407 | |
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408 | Here are examples of many kinds of file opens. Those using sysopen() |
409 | all assume |
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410 | |
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411 | use Fcntl; |
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412 | |
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413 | To open file for reading: |
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414 | |
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415 | open(FH, "< $path") || die $!; |
416 | sysopen(FH, $path, O_RDONLY) || die $!; |
417 | |
418 | To open file for writing, create new file if needed or else truncate old file: |
419 | |
420 | open(FH, "> $path") || die $!; |
421 | sysopen(FH, $path, O_WRONLY|O_TRUNC|O_CREAT) || die $!; |
422 | sysopen(FH, $path, O_WRONLY|O_TRUNC|O_CREAT, 0666) || die $!; |
423 | |
424 | To open file for writing, create new file, file must not exist: |
425 | |
426 | sysopen(FH, $path, O_WRONLY|O_EXCL|O_CREAT) || die $!; |
427 | sysopen(FH, $path, O_WRONLY|O_EXCL|O_CREAT, 0666) || die $!; |
428 | |
429 | To open file for appending, create if necessary: |
430 | |
431 | open(FH, ">> $path") || die $!; |
432 | sysopen(FH, $path, O_WRONLY|O_APPEND|O_CREAT) || die $!; |
433 | sysopen(FH, $path, O_WRONLY|O_APPEND|O_CREAT, 0666) || die $!; |
434 | |
435 | To open file for appending, file must exist: |
436 | |
437 | sysopen(FH, $path, O_WRONLY|O_APPEND) || die $!; |
438 | |
439 | To open file for update, file must exist: |
440 | |
441 | open(FH, "+< $path") || die $!; |
442 | sysopen(FH, $path, O_RDWR) || die $!; |
443 | |
444 | To open file for update, create file if necessary: |
445 | |
446 | sysopen(FH, $path, O_RDWR|O_CREAT) || die $!; |
447 | sysopen(FH, $path, O_RDWR|O_CREAT, 0666) || die $!; |
448 | |
449 | To open file for update, file must not exist: |
450 | |
451 | sysopen(FH, $path, O_RDWR|O_EXCL|O_CREAT) || die $!; |
452 | sysopen(FH, $path, O_RDWR|O_EXCL|O_CREAT, 0666) || die $!; |
453 | |
454 | To open a file without blocking, creating if necessary: |
455 | |
456 | sysopen(FH, "/tmp/somefile", O_WRONLY|O_NDELAY|O_CREAT) |
457 | or die "can't open /tmp/somefile: $!": |
458 | |
459 | Be warned that neither creation nor deletion of files is guaranteed to |
460 | be an atomic operation over NFS. That is, two processes might both |
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461 | successfully create or unlink the same file! Therefore O_EXCL |
462 | isn't as exclusive as you might wish. |
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463 | |
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464 | See also the new L<perlopentut> if you have it (new for 5.6). |
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465 | |
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466 | =head2 Why do I sometimes get an "Argument list too long" when I use <*>? |
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467 | |
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468 | The C<< <> >> operator performs a globbing operation (see above). |
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469 | In Perl versions earlier than v5.6.0, the internal glob() operator forks |
470 | csh(1) to do the actual glob expansion, but |
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471 | csh can't handle more than 127 items and so gives the error message |
472 | C<Argument list too long>. People who installed tcsh as csh won't |
473 | have this problem, but their users may be surprised by it. |
474 | |
3a4b19e4 |
475 | To get around this, either upgrade to Perl v5.6.0 or later, do the glob |
d6260402 |
476 | yourself with readdir() and patterns, or use a module like File::KGlob, |
3a4b19e4 |
477 | one that doesn't use the shell to do globbing. |
68dc0745 |
478 | |
479 | =head2 Is there a leak/bug in glob()? |
480 | |
481 | Due to the current implementation on some operating systems, when you |
482 | use the glob() function or its angle-bracket alias in a scalar |
a6dd486b |
483 | context, you may cause a memory leak and/or unpredictable behavior. It's |
68dc0745 |
484 | best therefore to use glob() only in list context. |
485 | |
c47ff5f1 |
486 | =head2 How can I open a file with a leading ">" or trailing blanks? |
68dc0745 |
487 | |
488 | Normally perl ignores trailing blanks in filenames, and interprets |
489 | certain leading characters (or a trailing "|") to mean something |
881bdbd4 |
490 | special. |
68dc0745 |
491 | |
881bdbd4 |
492 | The three argument form of open() lets you specify the mode |
493 | separately from the filename. The open() function treats |
494 | special mode characters and whitespace in the filename as |
495 | literals |
65acb1b1 |
496 | |
881bdbd4 |
497 | open FILE, "<", " file "; # filename is " file " |
498 | open FILE, ">", ">file"; # filename is ">file" |
65acb1b1 |
499 | |
881bdbd4 |
500 | It may be a lot clearer to use sysopen(), though: |
65acb1b1 |
501 | |
502 | use Fcntl; |
503 | $badpath = "<<<something really wicked "; |
a6dd486b |
504 | sysopen (FH, $badpath, O_WRONLY | O_CREAT | O_TRUNC) |
65acb1b1 |
505 | or die "can't open $badpath: $!"; |
68dc0745 |
506 | |
68dc0745 |
507 | =head2 How can I reliably rename a file? |
508 | |
d2321c93 |
509 | If your operating system supports a proper mv(1) utility or its functional |
d92eb7b0 |
510 | equivalent, this works: |
68dc0745 |
511 | |
512 | rename($old, $new) or system("mv", $old, $new); |
513 | |
d2321c93 |
514 | It may be more portable to use the File::Copy module instead. |
515 | You just copy to the new file to the new name (checking return |
516 | values), then delete the old one. This isn't really the same |
517 | semantically as a rename(), which preserves meta-information like |
68dc0745 |
518 | permissions, timestamps, inode info, etc. |
519 | |
d2321c93 |
520 | Newer versions of File::Copy export a move() function. |
5a964f20 |
521 | |
68dc0745 |
522 | =head2 How can I lock a file? |
523 | |
54310121 |
524 | Perl's builtin flock() function (see L<perlfunc> for details) will call |
68dc0745 |
525 | flock(2) if that exists, fcntl(2) if it doesn't (on perl version 5.004 and |
526 | later), and lockf(3) if neither of the two previous system calls exists. |
527 | On some systems, it may even use a different form of native locking. |
528 | Here are some gotchas with Perl's flock(): |
529 | |
530 | =over 4 |
531 | |
532 | =item 1 |
533 | |
534 | Produces a fatal error if none of the three system calls (or their |
535 | close equivalent) exists. |
536 | |
537 | =item 2 |
538 | |
539 | lockf(3) does not provide shared locking, and requires that the |
540 | filehandle be open for writing (or appending, or read/writing). |
541 | |
542 | =item 3 |
543 | |
d92eb7b0 |
544 | Some versions of flock() can't lock files over a network (e.g. on NFS file |
545 | systems), so you'd need to force the use of fcntl(2) when you build Perl. |
a6dd486b |
546 | But even this is dubious at best. See the flock entry of L<perlfunc> |
d92eb7b0 |
547 | and the F<INSTALL> file in the source distribution for information on |
548 | building Perl to do this. |
549 | |
550 | Two potentially non-obvious but traditional flock semantics are that |
a6dd486b |
551 | it waits indefinitely until the lock is granted, and that its locks are |
d92eb7b0 |
552 | I<merely advisory>. Such discretionary locks are more flexible, but |
553 | offer fewer guarantees. This means that files locked with flock() may |
554 | be modified by programs that do not also use flock(). Cars that stop |
555 | for red lights get on well with each other, but not with cars that don't |
556 | stop for red lights. See the perlport manpage, your port's specific |
557 | documentation, or your system-specific local manpages for details. It's |
558 | best to assume traditional behavior if you're writing portable programs. |
a6dd486b |
559 | (If you're not, you should as always feel perfectly free to write |
d92eb7b0 |
560 | for your own system's idiosyncrasies (sometimes called "features"). |
561 | Slavish adherence to portability concerns shouldn't get in the way of |
562 | your getting your job done.) |
68dc0745 |
563 | |
13a2d996 |
564 | For more information on file locking, see also |
565 | L<perlopentut/"File Locking"> if you have it (new for 5.6). |
65acb1b1 |
566 | |
68dc0745 |
567 | =back |
568 | |
65acb1b1 |
569 | =head2 Why can't I just open(FH, ">file.lock")? |
68dc0745 |
570 | |
571 | A common bit of code B<NOT TO USE> is this: |
572 | |
573 | sleep(3) while -e "file.lock"; # PLEASE DO NOT USE |
574 | open(LCK, "> file.lock"); # THIS BROKEN CODE |
575 | |
576 | This is a classic race condition: you take two steps to do something |
577 | which must be done in one. That's why computer hardware provides an |
578 | atomic test-and-set instruction. In theory, this "ought" to work: |
579 | |
5a964f20 |
580 | sysopen(FH, "file.lock", O_WRONLY|O_EXCL|O_CREAT) |
68dc0745 |
581 | or die "can't open file.lock: $!": |
582 | |
583 | except that lamentably, file creation (and deletion) is not atomic |
584 | over NFS, so this won't work (at least, not every time) over the net. |
65acb1b1 |
585 | Various schemes involving link() have been suggested, but |
46fc3d4c |
586 | these tend to involve busy-wait, which is also subdesirable. |
68dc0745 |
587 | |
fc36a67e |
588 | =head2 I still don't get locking. I just want to increment the number in the file. How can I do this? |
68dc0745 |
589 | |
46fc3d4c |
590 | Didn't anyone ever tell you web-page hit counters were useless? |
5a964f20 |
591 | They don't count number of hits, they're a waste of time, and they serve |
a6dd486b |
592 | only to stroke the writer's vanity. It's better to pick a random number; |
593 | they're more realistic. |
68dc0745 |
594 | |
5a964f20 |
595 | Anyway, this is what you can do if you can't help yourself. |
68dc0745 |
596 | |
e2c57c3e |
597 | use Fcntl qw(:DEFAULT :flock); |
5a964f20 |
598 | sysopen(FH, "numfile", O_RDWR|O_CREAT) or die "can't open numfile: $!"; |
65acb1b1 |
599 | flock(FH, LOCK_EX) or die "can't flock numfile: $!"; |
68dc0745 |
600 | $num = <FH> || 0; |
601 | seek(FH, 0, 0) or die "can't rewind numfile: $!"; |
602 | truncate(FH, 0) or die "can't truncate numfile: $!"; |
603 | (print FH $num+1, "\n") or die "can't write numfile: $!"; |
68dc0745 |
604 | close FH or die "can't close numfile: $!"; |
605 | |
46fc3d4c |
606 | Here's a much better web-page hit counter: |
68dc0745 |
607 | |
608 | $hits = int( (time() - 850_000_000) / rand(1_000) ); |
609 | |
610 | If the count doesn't impress your friends, then the code might. :-) |
611 | |
f52f3be2 |
612 | =head2 All I want to do is append a small amount of text to the end of a file. Do I still have to use locking? |
05caf3a7 |
613 | |
614 | If you are on a system that correctly implements flock() and you use the |
615 | example appending code from "perldoc -f flock" everything will be OK |
616 | even if the OS you are on doesn't implement append mode correctly (if |
617 | such a system exists.) So if you are happy to restrict yourself to OSs |
618 | that implement flock() (and that's not really much of a restriction) |
619 | then that is what you should do. |
620 | |
621 | If you know you are only going to use a system that does correctly |
622 | implement appending (i.e. not Win32) then you can omit the seek() from |
623 | the above code. |
624 | |
625 | If you know you are only writing code to run on an OS and filesystem that |
626 | does implement append mode correctly (a local filesystem on a modern |
627 | Unix for example), and you keep the file in block-buffered mode and you |
628 | write less than one buffer-full of output between each manual flushing |
8305e449 |
629 | of the buffer then each bufferload is almost guaranteed to be written to |
05caf3a7 |
630 | the end of the file in one chunk without getting intermingled with |
631 | anyone else's output. You can also use the syswrite() function which is |
632 | simply a wrapper around your systems write(2) system call. |
633 | |
634 | There is still a small theoretical chance that a signal will interrupt |
635 | the system level write() operation before completion. There is also a |
636 | possibility that some STDIO implementations may call multiple system |
637 | level write()s even if the buffer was empty to start. There may be some |
638 | systems where this probability is reduced to zero. |
639 | |
68dc0745 |
640 | =head2 How do I randomly update a binary file? |
641 | |
642 | If you're just trying to patch a binary, in many cases something as |
643 | simple as this works: |
644 | |
645 | perl -i -pe 's{window manager}{window mangler}g' /usr/bin/emacs |
646 | |
647 | However, if you have fixed sized records, then you might do something more |
648 | like this: |
649 | |
650 | $RECSIZE = 220; # size of record, in bytes |
651 | $recno = 37; # which record to update |
652 | open(FH, "+<somewhere") || die "can't update somewhere: $!"; |
653 | seek(FH, $recno * $RECSIZE, 0); |
654 | read(FH, $record, $RECSIZE) == $RECSIZE || die "can't read record $recno: $!"; |
655 | # munge the record |
65acb1b1 |
656 | seek(FH, -$RECSIZE, 1); |
68dc0745 |
657 | print FH $record; |
658 | close FH; |
659 | |
660 | Locking and error checking are left as an exercise for the reader. |
a6dd486b |
661 | Don't forget them or you'll be quite sorry. |
68dc0745 |
662 | |
68dc0745 |
663 | =head2 How do I get a file's timestamp in perl? |
664 | |
881bdbd4 |
665 | If you want to retrieve the time at which the file was last |
666 | read, written, or had its meta-data (owner, etc) changed, |
667 | you use the B<-M>, B<-A>, or B<-C> file test operations as |
668 | documented in L<perlfunc>. These retrieve the age of the |
669 | file (measured against the start-time of your program) in |
670 | days as a floating point number. Some platforms may not have |
671 | all of these times. See L<perlport> for details. To |
672 | retrieve the "raw" time in seconds since the epoch, you |
673 | would call the stat function, then use localtime(), |
674 | gmtime(), or POSIX::strftime() to convert this into |
675 | human-readable form. |
68dc0745 |
676 | |
677 | Here's an example: |
678 | |
679 | $write_secs = (stat($file))[9]; |
c8db1d39 |
680 | printf "file %s updated at %s\n", $file, |
681 | scalar localtime($write_secs); |
68dc0745 |
682 | |
683 | If you prefer something more legible, use the File::stat module |
684 | (part of the standard distribution in version 5.004 and later): |
685 | |
65acb1b1 |
686 | # error checking left as an exercise for reader. |
68dc0745 |
687 | use File::stat; |
688 | use Time::localtime; |
689 | $date_string = ctime(stat($file)->mtime); |
690 | print "file $file updated at $date_string\n"; |
691 | |
65acb1b1 |
692 | The POSIX::strftime() approach has the benefit of being, |
693 | in theory, independent of the current locale. See L<perllocale> |
694 | for details. |
68dc0745 |
695 | |
696 | =head2 How do I set a file's timestamp in perl? |
697 | |
698 | You use the utime() function documented in L<perlfunc/utime>. |
699 | By way of example, here's a little program that copies the |
700 | read and write times from its first argument to all the rest |
701 | of them. |
702 | |
703 | if (@ARGV < 2) { |
704 | die "usage: cptimes timestamp_file other_files ...\n"; |
705 | } |
706 | $timestamp = shift; |
707 | ($atime, $mtime) = (stat($timestamp))[8,9]; |
708 | utime $atime, $mtime, @ARGV; |
709 | |
65acb1b1 |
710 | Error checking is, as usual, left as an exercise for the reader. |
68dc0745 |
711 | |
712 | Note that utime() currently doesn't work correctly with Win95/NT |
713 | ports. A bug has been reported. Check it carefully before using |
a6dd486b |
714 | utime() on those platforms. |
68dc0745 |
715 | |
716 | =head2 How do I print to more than one file at once? |
717 | |
718 | If you only have to do this once, you can do this: |
719 | |
720 | for $fh (FH1, FH2, FH3) { print $fh "whatever\n" } |
721 | |
722 | To connect up to one filehandle to several output filehandles, it's |
723 | easiest to use the tee(1) program if you have it, and let it take care |
724 | of the multiplexing: |
725 | |
726 | open (FH, "| tee file1 file2 file3"); |
727 | |
5a964f20 |
728 | Or even: |
729 | |
730 | # make STDOUT go to three files, plus original STDOUT |
731 | open (STDOUT, "| tee file1 file2 file3") or die "Teeing off: $!\n"; |
732 | print "whatever\n" or die "Writing: $!\n"; |
733 | close(STDOUT) or die "Closing: $!\n"; |
68dc0745 |
734 | |
5a964f20 |
735 | Otherwise you'll have to write your own multiplexing print |
a6dd486b |
736 | function--or your own tee program--or use Tom Christiansen's, |
a93751fa |
737 | at http://www.cpan.org/authors/id/TOMC/scripts/tct.gz , which is |
5a964f20 |
738 | written in Perl and offers much greater functionality |
739 | than the stock version. |
68dc0745 |
740 | |
d92eb7b0 |
741 | =head2 How can I read in an entire file all at once? |
742 | |
743 | The customary Perl approach for processing all the lines in a file is to |
744 | do so one line at a time: |
745 | |
746 | open (INPUT, $file) || die "can't open $file: $!"; |
747 | while (<INPUT>) { |
748 | chomp; |
749 | # do something with $_ |
750 | } |
751 | close(INPUT) || die "can't close $file: $!"; |
752 | |
753 | This is tremendously more efficient than reading the entire file into |
754 | memory as an array of lines and then processing it one element at a time, |
a6dd486b |
755 | which is often--if not almost always--the wrong approach. Whenever |
d92eb7b0 |
756 | you see someone do this: |
757 | |
758 | @lines = <INPUT>; |
759 | |
a6dd486b |
760 | you should think long and hard about why you need everything loaded |
d92eb7b0 |
761 | at once. It's just not a scalable solution. You might also find it |
106325ad |
762 | more fun to use the standard DB_File module's $DB_RECNO bindings, |
d92eb7b0 |
763 | which allow you to tie an array to a file so that accessing an element |
764 | the array actually accesses the corresponding line in the file. |
765 | |
766 | On very rare occasion, you may have an algorithm that demands that |
767 | the entire file be in memory at once as one scalar. The simplest solution |
a6dd486b |
768 | to that is |
d92eb7b0 |
769 | |
770 | $var = `cat $file`; |
771 | |
772 | Being in scalar context, you get the whole thing. In list context, |
773 | you'd get a list of all the lines: |
774 | |
775 | @lines = `cat $file`; |
776 | |
87275199 |
777 | This tiny but expedient solution is neat, clean, and portable to |
778 | all systems on which decent tools have been installed. For those |
779 | who prefer not to use the toolbox, you can of course read the file |
780 | manually, although this makes for more complicated code. |
d92eb7b0 |
781 | |
782 | { |
783 | local(*INPUT, $/); |
784 | open (INPUT, $file) || die "can't open $file: $!"; |
785 | $var = <INPUT>; |
786 | } |
787 | |
788 | That temporarily undefs your record separator, and will automatically |
789 | close the file at block exit. If the file is already open, just use this: |
790 | |
791 | $var = do { local $/; <INPUT> }; |
792 | |
68dc0745 |
793 | =head2 How can I read in a file by paragraphs? |
794 | |
65acb1b1 |
795 | Use the C<$/> variable (see L<perlvar> for details). You can either |
68dc0745 |
796 | set it to C<""> to eliminate empty paragraphs (C<"abc\n\n\n\ndef">, |
797 | for instance, gets treated as two paragraphs and not three), or |
798 | C<"\n\n"> to accept empty paragraphs. |
799 | |
d05ac700 |
800 | Note that a blank line must have no blanks in it. Thus |
c4db748a |
801 | S<C<"fred\n \nstuff\n\n">> is one paragraph, but C<"fred\n\nstuff\n\n"> is two. |
65acb1b1 |
802 | |
68dc0745 |
803 | =head2 How can I read a single character from a file? From the keyboard? |
804 | |
805 | You can use the builtin C<getc()> function for most filehandles, but |
806 | it won't (easily) work on a terminal device. For STDIN, either use |
a6dd486b |
807 | the Term::ReadKey module from CPAN or use the sample code in |
68dc0745 |
808 | L<perlfunc/getc>. |
809 | |
65acb1b1 |
810 | If your system supports the portable operating system programming |
811 | interface (POSIX), you can use the following code, which you'll note |
812 | turns off echo processing as well. |
68dc0745 |
813 | |
814 | #!/usr/bin/perl -w |
815 | use strict; |
816 | $| = 1; |
817 | for (1..4) { |
818 | my $got; |
819 | print "gimme: "; |
820 | $got = getone(); |
821 | print "--> $got\n"; |
822 | } |
823 | exit; |
824 | |
825 | BEGIN { |
826 | use POSIX qw(:termios_h); |
827 | |
828 | my ($term, $oterm, $echo, $noecho, $fd_stdin); |
829 | |
830 | $fd_stdin = fileno(STDIN); |
831 | |
832 | $term = POSIX::Termios->new(); |
833 | $term->getattr($fd_stdin); |
834 | $oterm = $term->getlflag(); |
835 | |
836 | $echo = ECHO | ECHOK | ICANON; |
837 | $noecho = $oterm & ~$echo; |
838 | |
839 | sub cbreak { |
840 | $term->setlflag($noecho); |
841 | $term->setcc(VTIME, 1); |
842 | $term->setattr($fd_stdin, TCSANOW); |
843 | } |
844 | |
845 | sub cooked { |
846 | $term->setlflag($oterm); |
847 | $term->setcc(VTIME, 0); |
848 | $term->setattr($fd_stdin, TCSANOW); |
849 | } |
850 | |
851 | sub getone { |
852 | my $key = ''; |
853 | cbreak(); |
854 | sysread(STDIN, $key, 1); |
855 | cooked(); |
856 | return $key; |
857 | } |
858 | |
859 | } |
860 | |
861 | END { cooked() } |
862 | |
a6dd486b |
863 | The Term::ReadKey module from CPAN may be easier to use. Recent versions |
65acb1b1 |
864 | include also support for non-portable systems as well. |
68dc0745 |
865 | |
866 | use Term::ReadKey; |
867 | open(TTY, "</dev/tty"); |
868 | print "Gimme a char: "; |
869 | ReadMode "raw"; |
870 | $key = ReadKey 0, *TTY; |
871 | ReadMode "normal"; |
872 | printf "\nYou said %s, char number %03d\n", |
873 | $key, ord $key; |
874 | |
65acb1b1 |
875 | =head2 How can I tell whether there's a character waiting on a filehandle? |
68dc0745 |
876 | |
5a964f20 |
877 | The very first thing you should do is look into getting the Term::ReadKey |
65acb1b1 |
878 | extension from CPAN. As we mentioned earlier, it now even has limited |
879 | support for non-portable (read: not open systems, closed, proprietary, |
880 | not POSIX, not Unix, etc) systems. |
5a964f20 |
881 | |
882 | You should also check out the Frequently Asked Questions list in |
68dc0745 |
883 | comp.unix.* for things like this: the answer is essentially the same. |
884 | It's very system dependent. Here's one solution that works on BSD |
885 | systems: |
886 | |
887 | sub key_ready { |
888 | my($rin, $nfd); |
889 | vec($rin, fileno(STDIN), 1) = 1; |
890 | return $nfd = select($rin,undef,undef,0); |
891 | } |
892 | |
65acb1b1 |
893 | If you want to find out how many characters are waiting, there's |
894 | also the FIONREAD ioctl call to be looked at. The I<h2ph> tool that |
895 | comes with Perl tries to convert C include files to Perl code, which |
896 | can be C<require>d. FIONREAD ends up defined as a function in the |
897 | I<sys/ioctl.ph> file: |
68dc0745 |
898 | |
5a964f20 |
899 | require 'sys/ioctl.ph'; |
68dc0745 |
900 | |
5a964f20 |
901 | $size = pack("L", 0); |
902 | ioctl(FH, FIONREAD(), $size) or die "Couldn't call ioctl: $!\n"; |
903 | $size = unpack("L", $size); |
68dc0745 |
904 | |
5a964f20 |
905 | If I<h2ph> wasn't installed or doesn't work for you, you can |
906 | I<grep> the include files by hand: |
68dc0745 |
907 | |
5a964f20 |
908 | % grep FIONREAD /usr/include/*/* |
909 | /usr/include/asm/ioctls.h:#define FIONREAD 0x541B |
68dc0745 |
910 | |
5a964f20 |
911 | Or write a small C program using the editor of champions: |
68dc0745 |
912 | |
5a964f20 |
913 | % cat > fionread.c |
914 | #include <sys/ioctl.h> |
915 | main() { |
916 | printf("%#08x\n", FIONREAD); |
917 | } |
918 | ^D |
65acb1b1 |
919 | % cc -o fionread fionread.c |
5a964f20 |
920 | % ./fionread |
921 | 0x4004667f |
922 | |
8305e449 |
923 | And then hard code it, leaving porting as an exercise to your successor. |
5a964f20 |
924 | |
925 | $FIONREAD = 0x4004667f; # XXX: opsys dependent |
926 | |
927 | $size = pack("L", 0); |
928 | ioctl(FH, $FIONREAD, $size) or die "Couldn't call ioctl: $!\n"; |
929 | $size = unpack("L", $size); |
930 | |
a6dd486b |
931 | FIONREAD requires a filehandle connected to a stream, meaning that sockets, |
5a964f20 |
932 | pipes, and tty devices work, but I<not> files. |
68dc0745 |
933 | |
934 | =head2 How do I do a C<tail -f> in perl? |
935 | |
936 | First try |
937 | |
938 | seek(GWFILE, 0, 1); |
939 | |
940 | The statement C<seek(GWFILE, 0, 1)> doesn't change the current position, |
941 | but it does clear the end-of-file condition on the handle, so that the |
942 | next <GWFILE> makes Perl try again to read something. |
943 | |
944 | If that doesn't work (it relies on features of your stdio implementation), |
945 | then you need something more like this: |
946 | |
947 | for (;;) { |
948 | for ($curpos = tell(GWFILE); <GWFILE>; $curpos = tell(GWFILE)) { |
949 | # search for some stuff and put it into files |
950 | } |
951 | # sleep for a while |
952 | seek(GWFILE, $curpos, 0); # seek to where we had been |
953 | } |
954 | |
955 | If this still doesn't work, look into the POSIX module. POSIX defines |
956 | the clearerr() method, which can remove the end of file condition on a |
957 | filehandle. The method: read until end of file, clearerr(), read some |
958 | more. Lather, rinse, repeat. |
959 | |
65acb1b1 |
960 | There's also a File::Tail module from CPAN. |
961 | |
68dc0745 |
962 | =head2 How do I dup() a filehandle in Perl? |
963 | |
964 | If you check L<perlfunc/open>, you'll see that several of the ways |
965 | to call open() should do the trick. For example: |
966 | |
967 | open(LOG, ">>/tmp/logfile"); |
968 | open(STDERR, ">&LOG"); |
969 | |
970 | Or even with a literal numeric descriptor: |
971 | |
972 | $fd = $ENV{MHCONTEXTFD}; |
973 | open(MHCONTEXT, "<&=$fd"); # like fdopen(3S) |
974 | |
c47ff5f1 |
975 | Note that "<&STDIN" makes a copy, but "<&=STDIN" make |
5a964f20 |
976 | an alias. That means if you close an aliased handle, all |
977 | aliases become inaccessible. This is not true with |
978 | a copied one. |
979 | |
980 | Error checking, as always, has been left as an exercise for the reader. |
68dc0745 |
981 | |
982 | =head2 How do I close a file descriptor by number? |
983 | |
984 | This should rarely be necessary, as the Perl close() function is to be |
985 | used for things that Perl opened itself, even if it was a dup of a |
a6dd486b |
986 | numeric descriptor as with MHCONTEXT above. But if you really have |
68dc0745 |
987 | to, you may be able to do this: |
988 | |
989 | require 'sys/syscall.ph'; |
990 | $rc = syscall(&SYS_close, $fd + 0); # must force numeric |
991 | die "can't sysclose $fd: $!" unless $rc == -1; |
992 | |
a6dd486b |
993 | Or, just use the fdopen(3S) feature of open(): |
d92eb7b0 |
994 | |
995 | { |
996 | local *F; |
997 | open F, "<&=$fd" or die "Cannot reopen fd=$fd: $!"; |
998 | close F; |
999 | } |
1000 | |
883f1635 |
1001 | =head2 Why can't I use "C:\temp\foo" in DOS paths? Why doesn't `C:\temp\foo.exe` work? |
68dc0745 |
1002 | |
1003 | Whoops! You just put a tab and a formfeed into that filename! |
1004 | Remember that within double quoted strings ("like\this"), the |
1005 | backslash is an escape character. The full list of these is in |
1006 | L<perlop/Quote and Quote-like Operators>. Unsurprisingly, you don't |
1007 | have a file called "c:(tab)emp(formfeed)oo" or |
65acb1b1 |
1008 | "c:(tab)emp(formfeed)oo.exe" on your legacy DOS filesystem. |
68dc0745 |
1009 | |
1010 | Either single-quote your strings, or (preferably) use forward slashes. |
46fc3d4c |
1011 | Since all DOS and Windows versions since something like MS-DOS 2.0 or so |
68dc0745 |
1012 | have treated C</> and C<\> the same in a path, you might as well use the |
a6dd486b |
1013 | one that doesn't clash with Perl--or the POSIX shell, ANSI C and C++, |
65acb1b1 |
1014 | awk, Tcl, Java, or Python, just to mention a few. POSIX paths |
1015 | are more portable, too. |
68dc0745 |
1016 | |
1017 | =head2 Why doesn't glob("*.*") get all the files? |
1018 | |
1019 | Because even on non-Unix ports, Perl's glob function follows standard |
46fc3d4c |
1020 | Unix globbing semantics. You'll need C<glob("*")> to get all (non-hidden) |
65acb1b1 |
1021 | files. This makes glob() portable even to legacy systems. Your |
1022 | port may include proprietary globbing functions as well. Check its |
1023 | documentation for details. |
68dc0745 |
1024 | |
1025 | =head2 Why does Perl let me delete read-only files? Why does C<-i> clobber protected files? Isn't this a bug in Perl? |
1026 | |
06a5f41f |
1027 | This is elaborately and painstakingly described in the |
1028 | F<file-dir-perms> article in the "Far More Than You Ever Wanted To |
1029 | Know" collection in http://www.cpan.org/olddoc/FMTEYEWTK.tgz . |
68dc0745 |
1030 | |
1031 | The executive summary: learn how your filesystem works. The |
1032 | permissions on a file say what can happen to the data in that file. |
1033 | The permissions on a directory say what can happen to the list of |
1034 | files in that directory. If you delete a file, you're removing its |
1035 | name from the directory (so the operation depends on the permissions |
1036 | of the directory, not of the file). If you try to write to the file, |
1037 | the permissions of the file govern whether you're allowed to. |
1038 | |
1039 | =head2 How do I select a random line from a file? |
1040 | |
1041 | Here's an algorithm from the Camel Book: |
1042 | |
1043 | srand; |
1044 | rand($.) < 1 && ($line = $_) while <>; |
1045 | |
1046 | This has a significant advantage in space over reading the whole |
5a964f20 |
1047 | file in. A simple proof by induction is available upon |
a6dd486b |
1048 | request if you doubt the algorithm's correctness. |
68dc0745 |
1049 | |
65acb1b1 |
1050 | =head2 Why do I get weird spaces when I print an array of lines? |
1051 | |
1052 | Saying |
1053 | |
1054 | print "@lines\n"; |
1055 | |
1056 | joins together the elements of C<@lines> with a space between them. |
1057 | If C<@lines> were C<("little", "fluffy", "clouds")> then the above |
a6dd486b |
1058 | statement would print |
65acb1b1 |
1059 | |
1060 | little fluffy clouds |
1061 | |
1062 | but if each element of C<@lines> was a line of text, ending a newline |
1063 | character C<("little\n", "fluffy\n", "clouds\n")> then it would print: |
1064 | |
1065 | little |
1066 | fluffy |
1067 | clouds |
1068 | |
1069 | If your array contains lines, just print them: |
1070 | |
1071 | print @lines; |
1072 | |
68dc0745 |
1073 | =head1 AUTHOR AND COPYRIGHT |
1074 | |
0bc0ad85 |
1075 | Copyright (c) 1997-2002 Tom Christiansen and Nathan Torkington. |
5a964f20 |
1076 | All rights reserved. |
1077 | |
5a7beb56 |
1078 | This documentation is free; you can redistribute it and/or modify it |
1079 | under the same terms as Perl itself. |
c8db1d39 |
1080 | |
87275199 |
1081 | Irrespective of its distribution, all code examples here are in the public |
c8db1d39 |
1082 | domain. You are permitted and encouraged to use this code and any |
1083 | derivatives thereof in your own programs for fun or for profit as you |
1084 | see fit. A simple comment in the code giving credit to the FAQ would |
1085 | be courteous but is not required. |