X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlfunc.pod;h=39b09449c378472866dfda681f78385b98f348ab;hb=adf5897a9c5a95830162479dac5d96b5a05d0c3b;hp=f509f6155366ea92d6042c604c755b1341306e95;hpb=2c268ad5f2bec64cb74406f2e1af30ddc0dc3b9f;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlfunc.pod b/pod/perlfunc.pod index f509f61..39b0944 100644 --- a/pod/perlfunc.pod +++ b/pod/perlfunc.pod @@ -1,4 +1,3 @@ - =head1 NAME perlfunc - Perl builtin functions @@ -53,26 +52,36 @@ nonabortive failure is generally indicated in a scalar context by returning the undefined value, and in a list context by returning the null list. -Remember the following rule: - -=over 8 - -=item I - -=back - +Remember the following important rule: There is B that relates +the behavior of an expression in list context to its behavior in scalar +context, or vice versa. It might do two totally different things. Each operator and function decides which sort of value it would be most appropriate to return in a scalar context. Some operators return the -length of the list that would have been returned in a list context. Some +length of the list that would have been returned in list context. Some operators return the first value in the list. Some operators return the last value in the list. Some operators return a count of successful operations. In general, they do what you want, unless you want consistency. +An named array in scalar context is quite different from what would at +first glance appear to be a list in scalar context. You can't get a list +like C<(1,2,3)> into being in scalar context, because the compiler knows +the context at compile time. It would generate the scalar comma operator +there, not the list construction version of the comma. That means it +was never a list to start with. + +In general, functions in Perl that serve as wrappers for system calls +of the same name (like chown(2), fork(2), closedir(2), etc.) all return +true when they succeed and C otherwise, as is usually mentioned +in the descriptions below. This is different from the C interfaces, +which return C<-1> on failure. Exceptions to this rule are C, +C, and C. System calls also set the special C<$!> +variable on failure. Other functions do not, except accidentally. + =head2 Perl Functions by Category Here are Perl's functions (including things that look like -functions, like some of the keywords and named operators) +functions, like some keywords and named operators) arranged by category. Some functions appear in more than one place. @@ -81,12 +90,12 @@ than one place. =item Functions for SCALARs or strings C, C, C, C, C, C, C, C, -C, C, C, C, C/STRING/, C/STRING/, C, -C, C, C, C, C, C, C/// +C, C, C, C, C, C, C, +C, C, C, C, C, C, C =item Regular expressions and pattern matching -C//, C, C, C///, C, C +C, C, C, C, C, C, C =item Numeric functions @@ -99,7 +108,7 @@ C, C, C, C, C =item Functions for list data -C, C, C, C/STRING/, C, C, C +C, C, C, C, C, C, C =item Functions for real %HASHes @@ -140,7 +149,7 @@ C, C, C =item Functions for processes and process groups C, C, C, C, C, C, C, -C, C/STRING/, C, C, C, C, +C, C, C, C, C, C, C, C, C =item Keywords related to perl modules @@ -189,7 +198,7 @@ C, C, C, C, C, C, C, C, C, C, C, C * - C was a keyword in perl4, but in perl5 it is an -operator which can be used in expressions. +operator, which can be used in expressions. =item Functions obsoleted in perl5 @@ -210,7 +219,7 @@ C, C A file test, where X is one of the letters listed below. This unary operator takes one argument, either a filename or a filehandle, and tests the associated file to see if something is true about it. If the -argument is omitted, tests $_, except for C<-t>, which tests STDIN. +argument is omitted, tests C<$_>, except for C<-t>, which tests STDIN. Unless otherwise documented, it returns C<1> for TRUE and C<''> for FALSE, or the undefined value if the file doesn't exist. Despite the funny names, precedence is the same as any other named unary operator, and @@ -234,7 +243,7 @@ operator may be any of: -f File is a plain file. -d File is a directory. -l File is a symbolic link. - -p File is a named pipe (FIFO). + -p File is a named pipe (FIFO), or Filehandle is a pipe. -S File is a socket. -b File is a block special file. -c File is a character special file. @@ -254,10 +263,10 @@ operator may be any of: The interpretation of the file permission operators C<-r>, C<-R>, C<-w>, C<-W>, C<-x>, and C<-X> is based solely on the mode of the file and the uids and gids of the user. There may be other reasons you can't actually -read, write or execute the file. Also note that, for the superuser, -C<-r>, C<-R>, C<-w>, and C<-W> always return 1, and C<-x> and C<-X> return -1 if any execute bit is set in the mode. Scripts run by the superuser may -thus need to do a stat() to determine the actual mode of the +read, write, or execute the file, such as AFS access control lists. Also note that, for the superuser, +C<-r>, C<-R>, C<-w>, and C<-W> always return C<1>, and C<-x> and C<-X> return +C<1> if any execute bit is set in the mode. Scripts run by the superuser may +thus need to do a C to determine the actual mode of the file, or temporarily set the uid to something else. Example: @@ -265,7 +274,7 @@ Example: while (<>) { chop; next unless -f $_; # ignore specials - ... + #... } Note that C<-s/a/b/> does not do a negated substitution. Saying @@ -274,7 +283,7 @@ following a minus are interpreted as file tests. The C<-T> and C<-B> switches work as follows. The first block or so of the file is examined for odd characters such as strange control codes or -characters with the high bit set. If too many odd characters (E30%) +characters with the high bit set. If too many strange characters (E30%) are found, it's a C<-B> file, otherwise it's a C<-T> file. Also, any file containing null in the first block is considered a binary file. If C<-T> or C<-B> is used on a filehandle, the current stdio buffer is examined @@ -283,7 +292,7 @@ file, or a file at EOF when testing a filehandle. Because you have to read a file to do the C<-T> test, on most occasions you want to use a C<-f> against the file first, as in C. -If any of the file tests (or either the stat() or lstat() operators) are given +If any of the file tests (or either the C or C operators) are given the special filehandle consisting of a solitary underline, then the stat structure of the previous file test (or stat operator) is used, saving a system call. (This doesn't work with C<-t>, and you need to remember @@ -307,7 +316,7 @@ symbolic link, not the real file.) Example: =item abs Returns the absolute value of its argument. -If VALUE is omitted, uses $_. +If VALUE is omitted, uses C<$_>. =item accept NEWSOCKET,GENERICSOCKET @@ -321,32 +330,33 @@ See example in L. Arranges to have a SIGALRM delivered to this process after the specified number of seconds have elapsed. If SECONDS is not specified, -the value stored in $_ is used. (On some machines, +the value stored in C<$_> is used. (On some machines, unfortunately, the elapsed time may be up to one second less than you specified because of how seconds are counted.) Only one timer may be counting at once. Each call disables the previous timer, and an -argument of 0 may be supplied to cancel the previous timer without +argument of C<0> may be supplied to cancel the previous timer without starting a new one. The returned value is the amount of time remaining on the previous timer. For delays of finer granularity than one second, you may use Perl's -syscall() interface to access setitimer(2) if your system supports it, -or else see L. It is usually a mistake to intermix alarm() -and sleep() calls. +C interface to access setitimer(2) if your system supports it, +or else see L. It is usually a mistake to intermix C +and C calls. -If you want to use alarm() to time out a system call you need to use an -eval/die pair. You can't rely on the alarm causing the system call to -fail with $! set to EINTR because Perl sets up signal handlers to -restart system calls on some systems. Using eval/die always works. +If you want to use C to time out a system call you need to use an +C/C pair. You can't rely on the alarm causing the system call to +fail with C<$!> set to C because Perl sets up signal handlers to +restart system calls on some systems. Using C/C always works, +modulo the caveats given in L. eval { - local $SIG{ALRM} = sub { die "alarm\n" }; # NB \n required + local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required alarm $timeout; $nread = sysread SOCKET, $buffer, $size; alarm 0; }; - die if $@ && $@ ne "alarm\n"; # propagate errors if ($@) { + die unless $@ eq "alarm\n"; # propagate unexpected errors # timed out } else { @@ -357,7 +367,7 @@ restart system calls on some systems. Using eval/die always works. Returns the arctangent of Y/X in the range -PI to PI. -For the tangent operation, you may use the POSIX::tan() +For the tangent operation, you may use the C function, or use the familiar relation: sub tan { sin($_[0]) / cos($_[0]) } @@ -377,10 +387,10 @@ not in binary mode have CR LF sequences translated to LF on input and LF translated to CR LF on output. Binmode has no effect under Unix; in MS-DOS and similarly archaic systems, it may be imperative--otherwise your MS-DOS-damaged C library may mangle your file. The key distinction between -systems that need binmode and those that don't is their text file -formats. Systems like Unix and Plan9 that delimit lines with a single -character, and that encode that character in C as '\n', do not need -C. The rest need it. If FILEHANDLE is an expression, the value +systems that need C and those that don't is their text file +formats. Systems like Unix, MacOS, and Plan9 that delimit lines with a single +character, and that encode that character in C as C<"\n">, do not need +C. The rest need it. If FILEHANDLE is an expression, the value is taken as the name of the filehandle. =item bless REF,CLASSNAME @@ -390,19 +400,19 @@ is taken as the name of the filehandle. This function tells the thingy referenced by REF that it is now an object in the CLASSNAME package--or the current package if no CLASSNAME is specified, which is often the case. It returns the reference for -convenience, because a bless() is often the last thing in a constructor. +convenience, because a C is often the last thing in a constructor. Always use the two-argument version if the function doing the blessing -might be inherited by a derived class. See L for more about the -blessing (and blessings) of objects. +might be inherited by a derived class. See L and L +for more about the blessing (and blessings) of objects. =item caller EXPR =item caller -Returns the context of the current subroutine call. In a scalar context, +Returns the context of the current subroutine call. In scalar context, returns the caller's package name if there is a caller, that is, if -we're in a subroutine or eval() or require(), and the undefined value -otherwise. In a list context, returns +we're in a subroutine or C or C, and the undefined value +otherwise. In list context, returns ($package, $filename, $line) = caller; @@ -413,24 +423,30 @@ to go back before the current one. ($package, $filename, $line, $subroutine, $hasargs, $wantarray, $evaltext, $is_require) = caller($i); -Here $subroutine may be C<"(eval)"> if the frame is not a subroutine -call, but an C. In such a case additional elements $evaltext and -$is_require are set: $is_require is true if the frame is created by a -C or C statement, $evaltext contains the text of the +Here C<$subroutine> may be C<"(eval)"> if the frame is not a subroutine +call, but an C. In such a case additional elements C<$evaltext> and +C<$is_require> are set: C<$is_require> is true if the frame is created by a +C or C statement, C<$evaltext> contains the text of the C statement. In particular, for a C statement, -$filename is C<"(eval)">, but $evaltext is undefined. (Note also that +C<$filename> is C<"(eval)">, but C<$evaltext> is undefined. (Note also that each C statement creates a C frame inside an C) frame. Furthermore, when called from within the DB package, caller returns more -detailed information: it sets the list variable @DB::args to be the +detailed information: it sets the list variable C<@DB::args> to be the arguments with which the subroutine was invoked. +Be aware that the optimizer might have optimized call frames away before +C had a chance to get the information. That means that C +might not return information about the call frame you expect it do, for +C 1>. In particular, C<@DB::args> might have information from the +previous time C was called. + =item chdir EXPR Changes the working directory to EXPR, if possible. If EXPR is omitted, changes to home directory. Returns TRUE upon success, FALSE -otherwise. See example under die(). +otherwise. See example under C. =item chmod LIST @@ -442,7 +458,8 @@ successfully changed. See also L, if all you have is a string. $cnt = chmod 0755, 'foo', 'bar'; chmod 0755, @executables; - $mode = '0644'; chmod $mode, 'foo'; # !!! sets mode to --w----r-T + $mode = '0644'; chmod $mode, 'foo'; # !!! sets mode to + # --w----r-T $mode = '0644'; chmod oct($mode), 'foo'; # this is better $mode = 0644; chmod $mode, 'foo'; # this is best @@ -459,12 +476,12 @@ number of characters removed from all its arguments. It's often used to remove the newline from the end of an input record when you're worried that the final record may be missing its newline. When in paragraph mode (C<$/ = "">), it removes all trailing newlines from the string. If -VARIABLE is omitted, it chomps $_. Example: +VARIABLE is omitted, it chomps C<$_>. Example: while (<>) { chomp; # avoid \n on last field @array = split(/:/); - ... + # ... } You can actually chomp anything that's an lvalue, including an assignment: @@ -484,13 +501,13 @@ characters removed is returned. Chops off the last character of a string and returns the character chopped. It's used primarily to remove the newline from the end of an input record, but is much more efficient than C because it neither -scans nor copies the string. If VARIABLE is omitted, chops $_. +scans nor copies the string. If VARIABLE is omitted, chops C<$_>. Example: while (<>) { chop; # avoid \n on last field @array = split(/:/); - ... + #... } You can actually chop anything that's an lvalue, including an assignment: @@ -499,9 +516,9 @@ You can actually chop anything that's an lvalue, including an assignment: chop($answer = ); If you chop a list, each element is chopped. Only the value of the -last chop is returned. +last C is returned. -Note that chop returns the last character. To return all but the last +Note that C returns the last character. To return all but the last character, use C. =item chown LIST @@ -517,13 +534,13 @@ Here's an example that looks up nonnumeric uids in the passwd file: print "User: "; chop($user = ); - print "Files: " + print "Files: "; chop($pattern = ); ($login,$pass,$uid,$gid) = getpwnam($user) or die "$user not in passwd file"; - @ary = <${pattern}>; # expand filenames + @ary = glob($pattern); # expand filenames chown $uid, $gid, @ary; On most systems, you are not allowed to change the ownership of the @@ -536,55 +553,64 @@ restrictions may be relaxed, but this is not a portable assumption. =item chr Returns the character represented by that NUMBER in the character set. -For example, C is "A" in ASCII. For the reverse, use L. +For example, C is C<"A"> in ASCII. For the reverse, use L. -If NUMBER is omitted, uses $_. +If NUMBER is omitted, uses C<$_>. =item chroot FILENAME =item chroot -This function works as the system call by the same name: it makes the +This function works like the system call by the same name: it makes the named directory the new root directory for all further pathnames that -begin with a "/" by your process and all of its children. (It doesn't +begin with a C<"/"> by your process and all its children. (It doesn't change your current working directory, which is unaffected.) For security reasons, this call is restricted to the superuser. If FILENAME is -omitted, does chroot to $_. +omitted, does a C to C<$_>. =item close FILEHANDLE +=item close + Closes the file or pipe associated with the file handle, returning TRUE only if stdio successfully flushes buffers and closes the system file -descriptor. +descriptor. Closes the currently selected filehandle if the argument +is omitted. You don't have to close FILEHANDLE if you are immediately going to do -another open() on it, because open() will close it for you. (See -open().) However, an explicit close on an input file resets the line -counter ($.), while the implicit close done by open() does not. +another C on it, because C will close it for you. (See +C.) However, an explicit C on an input file resets the line +counter (C<$.>), while the implicit close done by C does not. -If the file handle came from a piped open C will additionally +If the file handle came from a piped open C will additionally return FALSE if one of the other system calls involved fails or if the program exits with non-zero status. (If the only problem was that the -program exited non-zero $! will be set to 0.) Also, closing a pipe will -wait for the process executing on the pipe to complete, in case you +program exited non-zero C<$!> will be set to C<0>.) Also, closing a pipe +waits for the process executing on the pipe to complete, in case you want to look at the output of the pipe afterwards. Closing a pipe explicitly also puts the exit status value of the command into C<$?>. + Example: open(OUTPUT, '|sort >foo') # pipe to sort or die "Can't start sort: $!"; - ... # print stuff to output + #... # print stuff to output close OUTPUT # wait for sort to finish or warn $! ? "Error closing sort pipe: $!" : "Exit status $? from sort"; open(INPUT, 'foo') # get sort's results or die "Can't open 'foo' for input: $!"; -FILEHANDLE may be an expression whose value gives the real filehandle name. +FILEHANDLE may be an expression whose value can be used as an indirect +filehandle, usually the real filehandle name. =item closedir DIRHANDLE -Closes a directory opened by opendir(). +Closes a directory opened by C and returns the success of that +system call. + +DIRHANDLE may be an expression whose value can be used as an indirect +dirhandle, usually the real dirhandle name. =item connect SOCKET,NAME @@ -603,12 +629,31 @@ it can be used to increment a loop variable, even when the loop has been continued via the C statement (which is similar to the C C statement). +C, C, or C may appear within a C +block. C and C will behave as if they had been executed within +the main block. So will C, but since it will execute a C +block, it may be more entertaining. + + while (EXPR) { + ### redo always comes here + do_something; + } continue { + ### next always comes here + do_something_else; + # then back the top to re-check EXPR + } + ### last always comes here + +Omitting the C section is semantically equivalent to using an +empty one, logically enough. In that case, C goes directly back +to check the condition at the top of the loop. + =item cos EXPR -Returns the cosine of EXPR (expressed in radians). If EXPR is omitted -takes cosine of $_. +Returns the cosine of EXPR (expressed in radians). If EXPR is omitted, +takes cosine of C<$_>. -For the inverse cosine operation, you may use the POSIX::acos() +For the inverse cosine operation, you may use the C function, or use this relation: sub acos { atan2( sqrt(1 - $_[0] * $_[0]), $_[0] ) } @@ -621,7 +666,7 @@ extirpated as a potential munition). This can prove useful for checking the password file for lousy passwords, amongst other things. Only the guys wearing white hats should do this. -Note that crypt is intended to be a one-way function, much like breaking +Note that C is intended to be a one-way function, much like breaking eggs to make an omelette. There is no (known) corresponding decrypt function. As a result, this function isn't all that useful for cryptography. (For that, see your nearby CPAN mirror.) @@ -649,32 +694,32 @@ for it is unwise. =item dbmclose HASH -[This function has been superseded by the untie() function.] +[This function has been superseded by the C function.] Breaks the binding between a DBM file and a hash. =item dbmopen HASH,DBNAME,MODE -[This function has been superseded by the tie() function.] +[This function has been superseded by the C function.] -This binds a dbm(3), ndbm(3), sdbm(3), gdbm(), or Berkeley DB file to a -hash. HASH is the name of the hash. (Unlike normal open, the first +This binds a dbm(3), ndbm(3), sdbm(3), gdbm(3), or Berkeley DB file to a +hash. HASH is the name of the hash. (Unlike normal C, the first argument is I a filehandle, even though it looks like one). DBNAME is the name of the database (without the F<.dir> or F<.pag> extension if any). If the database does not exist, it is created with protection -specified by MODE (as modified by the umask()). If your system supports -only the older DBM functions, you may perform only one dbmopen() in your +specified by MODE (as modified by the C). If your system supports +only the older DBM functions, you may perform only one C in your program. In older versions of Perl, if your system had neither DBM nor -ndbm, calling dbmopen() produced a fatal error; it now falls back to +ndbm, calling C produced a fatal error; it now falls back to sdbm(3). If you don't have write access to the DBM file, you can only read hash variables, not set them. If you want to test whether you can write, -either use file tests or try setting a dummy hash entry inside an eval(), +either use file tests or try setting a dummy hash entry inside an C, which will trap the error. -Note that functions such as keys() and values() may return huge array -values when used on large DBM files. You may prefer to use the each() +Note that functions such as C and C may return huge lists +when used on large DBM files. You may prefer to use the C function to iterate over large DBM files. Example: # print out history file offsets @@ -700,16 +745,16 @@ Many operations return C to indicate failure, end of file, system error, uninitialized variable, and other exceptional conditions. This function allows you to distinguish C from other values. (A simple Boolean test will not distinguish among -C, zero, the empty string, and "0", which are all equally +C, zero, the empty string, and C<"0">, which are all equally false.) Note that since C is a valid scalar, its presence -doesn't I indicate an exceptional condition: pop() +doesn't I indicate an exceptional condition: C returns C when its argument is an empty array, I when the element to return happens to be C. -You may also use defined() to check whether a subroutine exists. On -the other hand, use of defined() upon aggregates (hashes and arrays) -is not guaranteed to produce intuitive results, and should probably be -avoided. +You may also use C to check whether a subroutine exists, by +saying C without parentheses. On the other hand, use +of C upon aggregates (hashes and arrays) is not guaranteed to +produce intuitive results, and should probably be avoided. When used on a hash element, it tells you whether the value is defined, not whether the key exists in the hash. Use L for the latter @@ -724,22 +769,22 @@ Examples: sub foo { defined &$bar ? &$bar(@_) : die "No bar"; } $debugging = 0 unless defined $debugging; -Note: Many folks tend to overuse defined(), and then are surprised to -discover that the number 0 and "" (the zero-length string) are, in fact, +Note: Many folks tend to overuse C, and then are surprised to +discover that the number C<0> and C<""> (the zero-length string) are, in fact, defined values. For example, if you say "ab" =~ /a(.*)b/; -the pattern match succeeds, and $1 is defined, despite the fact that it +The pattern match succeeds, and C<$1> is defined, despite the fact that it matched "nothing". But it didn't really match nothing--rather, it -matched something that happened to be 0 characters long. This is all +matched something that happened to be C<0> characters long. This is all very above-board and honest. When a function returns an undefined value, it's an admission that it couldn't give you an honest answer. So you -should use defined() only when you're questioning the integrity of what -you're trying to do. At other times, a simple comparison to 0 or "" is +should use C only when you're questioning the integrity of what +you're trying to do. At other times, a simple comparison to C<0> or C<""> is what you want. -Currently, using defined() on an entire array or hash reports whether +Currently, using C on an entire array or hash reports whether memory for that aggregate has ever been allocated. So an array you set to the empty list appears undefined initially, and one that once was full and that you then set to the empty list still appears defined. You @@ -748,12 +793,13 @@ should instead use a simple test for size: if (@an_array) { print "has array elements\n" } if (%a_hash) { print "has hash members\n" } -Using undef() on these, however, does clear their memory and then report -them as not defined anymore, but you shoudln't do that unless you don't +Using C on these, however, does clear their memory and then report +them as not defined anymore, but you shouldn't do that unless you don't plan to use them again, because it saves time when you load them up -again to have memory already ready to be filled. +again to have memory already ready to be filled. The normal way to +free up space used by an aggregate is to assign the empty list. -This counterintuitive behaviour of defined() on aggregates may be +This counterintuitive behavior of C on aggregates may be changed, fixed, or broken in a future release of Perl. See also L, L, L. @@ -764,7 +810,7 @@ Deletes the specified key(s) and their associated values from a hash. For each key, returns the deleted value associated with that key, or the undefined value if there was no such key. Deleting from C<$ENV{}> modifies the environment. Deleting from a hash tied to a DBM file -deletes the entry from the DBM file. (But deleting from a tie()d hash +deletes the entry from the DBM file. (But deleting from a Cd hash doesn't necessarily return anything.) The following deletes all the values of a hash: @@ -777,21 +823,21 @@ And so does this: delete @HASH{keys %HASH} -(But both of these are slower than the undef() command.) Note that the -EXPR can be arbitrarily complicated as long as the final operation is a -hash element lookup or hash slice: +(But both of these are slower than just assigning the empty list, or +using C.) Note that the EXPR can be arbitrarily complicated as +long as the final operation is a hash element lookup or hash slice: delete $ref->[$x][$y]{$key}; delete @{$ref->[$x][$y]}{$key1, $key2, @morekeys}; =item die LIST -Outside of an eval(), prints the value of LIST to C and exits with -the current value of C<$!> (errno). If C<$!> is 0, exits with the value of +Outside an C, prints the value of LIST to C and exits with +the current value of C<$!> (errno). If C<$!> is C<0>, exits with the value of C<($? EE 8)> (backtick `command` status). If C<($? EE 8)> -is 0, exits with 255. Inside an eval(), the error message is stuffed into -C<$@>, and the eval() is terminated with the undefined value; this makes -die() the way to raise an exception. +is C<0>, exits with C<255>. Inside an C the error message is stuffed into +C<$@> and the C is terminated with the undefined value. This makes +C the way to raise an exception. Equivalent examples: @@ -800,8 +846,8 @@ Equivalent examples: If the value of EXPR does not end in a newline, the current script line number and input line number (if any) are also printed, and a newline -is supplied. Hint: sometimes appending ", stopped" to your message -will cause it to make better sense when the string "at foo line 123" is +is supplied. Hint: sometimes appending C<", stopped"> to your message +will cause it to make better sense when the string C<"at foo line 123"> is appended. Suppose you are running script "canasta". die "/etc/games is no good"; @@ -812,21 +858,21 @@ produce, respectively /etc/games is no good at canasta line 123. /etc/games is no good, stopped at canasta line 123. -See also exit() and warn(). +See also C and C. -If LIST is empty and $@ already contains a value (typically from a -previous eval) that value is reused after appending "\t...propagated". +If LIST is empty and C<$@> already contains a value (typically from a +previous eval) that value is reused after appending C<"\t...propagated">. This is useful for propagating exceptions: eval { ... }; die unless $@ =~ /Expected exception/; -If $@ is empty then the string "Died" is used. +If C<$@> is empty then the string C<"Died"> is used. -You can arrange for a callback to be called just before the die() does +You can arrange for a callback to be run just before the C does its deed, by setting the C<$SIG{__DIE__}> hook. The associated handler will be called with the error text and can change the error message, if -it sees fit, by calling die() again. See L for details on +it sees fit, by calling C again. See L for details on setting C<%SIG> entries, and L<"eval BLOCK"> for some examples. Note that the C<$SIG{__DIE__}> hook is called even inside eval()ed @@ -860,17 +906,38 @@ is just like scalar eval `cat stat.pl`; -except that it's more efficient, more concise, keeps track of the +except that it's more efficient and concise, keeps track of the current filename for error messages, and searches all the B<-I> libraries if the file isn't in the current directory (see also the @INC -array in L). It's the same, however, in that it does +array in L). It is also different in how +code evaluated with C doesn't see lexicals in the enclosing +scope like C does. It's the same, however, in that it does reparse the file every time you call it, so you probably don't want to do this inside a loop. +If C cannot read the file, it returns undef and sets C<$!> to the +error. If C can read the file but cannot compile it, it +returns undef and sets an error message in C<$@>. If the file is +successfully compiled, C returns the value of the last expression +evaluated. + Note that inclusion of library modules is better done with the -use() and require() operators, which also do error checking +C and C operators, which also do automatic error checking and raise an exception if there's a problem. +You might like to use C to read in a program configuration +file. Manual error checking can be done this way: + + # read in config files: system first, then user + for $file ("/share/prog/defaults.rc", + "$ENV{HOME}/.someprogrc") { + unless ($return = do $file) { + warn "couldn't parse $file: $@" if $@; + warn "couldn't do $file: $!" unless defined $return; + warn "couldn't run $file" unless $return; + } + } + =item dump LABEL This causes an immediate core dump. Primarily this is so that you can @@ -878,8 +945,8 @@ use the B program to turn your core dump into an executable binary after having initialized all your variables at the beginning of the program. When the new binary is executed it will begin by executing a C (with all the restrictions that C suffers). Think of -it as a goto with an intervening core dump and reincarnation. If LABEL -is omitted, restarts the program from the top. WARNING: any files +it as a goto with an intervening core dump and reincarnation. If C.) If EXPR is omitted, uses $_. +see L.) If EXPR is omitted, uses C<$_>. print hex '0xAf'; # prints '175' print hex 'aF'; # same =item import -There is no builtin import() function. It is merely an ordinary +There is no builtin C function. It is just an ordinary method (subroutine) defined (or inherited) by modules that wish to export -names to another module. The use() function calls the import() method +names to another module. The C function calls the C method for the package used. See also L, L, and L. =item index STR,SUBSTR,POSITION @@ -1605,15 +1789,19 @@ for the package used. See also L, L, and L. Returns the position of the first occurrence of SUBSTR in STR at or after POSITION. If POSITION is omitted, starts searching from the beginning of -the string. The return value is based at 0 (or whatever you've set the C<$[> +the string. The return value is based at C<0> (or whatever you've set the C<$[> variable to--but don't do that). If the substring is not found, returns -one less than the base, ordinarily -1. +one less than the base, ordinarily C<-1>. =item int EXPR =item int -Returns the integer portion of EXPR. If EXPR is omitted, uses $_. +Returns the integer portion of EXPR. If EXPR is omitted, uses C<$_>. +You should not use this for rounding, because it truncates +towards C<0>, and because machine representations of floating point +numbers can sometimes produce counterintuitive results. Usually C or C, +or the C or C functions, would serve you better. =item ioctl FILEHANDLE,FUNCTION,SCALAR @@ -1624,15 +1812,15 @@ Implements the ioctl(2) function. You'll probably have to say first to get the correct function definitions. If F doesn't exist or doesn't have the correct definitions you'll have to roll your own, based on your C header files such as Fsys/ioctl.hE>. -(There is a Perl script called B that comes with the Perl kit which +(There is a Perl script called B that comes with the Perl kit that may help you in this, but it's nontrivial.) SCALAR will be read and/or written depending on the FUNCTION--a pointer to the string value of SCALAR -will be passed as the third argument of the actual ioctl call. (If SCALAR +will be passed as the third argument of the actual C call. (If SCALAR has no string value but does have a numeric value, that value will be passed rather than a pointer to the string value. To guarantee this to be -TRUE, add a 0 to the scalar before using it.) The pack() and unpack() +TRUE, add a C<0> to the scalar before using it.) The C and C functions are useful for manipulating the values of structures used by -ioctl(). The following example sets the erase character to DEL. +C. The following example sets the erase character to DEL. require 'ioctl.ph'; $getp = &TIOCGETP; @@ -1646,7 +1834,7 @@ ioctl(). The following example sets the erase character to DEL. || die "Can't ioctl: $!"; } -The return value of ioctl (and fcntl) is as follows: +The return value of C (and C) is as follows: if OS returns: then Perl returns: -1 undefined value @@ -1660,6 +1848,9 @@ system: ($retval = ioctl(...)) || ($retval = -1); printf "System returned %d\n", $retval; +The special string "C<0> but true" is excempt from B<-w> complaints +about improper numeric conversions. + =item join EXPR,LIST Joins the separate strings of LIST into a single string with @@ -1668,14 +1859,14 @@ Example: $_ = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell); -See L. +See L. =item keys HASH -Returns a normal array consisting of all the keys of the named hash. (In -a scalar context, returns the number of keys.) The keys are returned in +Returns a list consisting of all the keys of the named hash. (In a +scalar context, returns the number of keys.) The keys are returned in an apparently random order, but it is the same order as either the -values() or each() function produces (given that the hash has not been +C or C function produces (given that the hash has not been modified). As a side effect, it resets HASH's iterator. Here is yet another way to print your environment: @@ -1692,25 +1883,26 @@ or how about sorted by key: print $key, '=', $ENV{$key}, "\n"; } -To sort an array by value, you'll need to use a C function. +To sort an array by value, you'll need to use a C function. Here's a descending numeric sort of a hash by its values: - foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash)) { + foreach $key (sort { $hash{$b} <=> $hash{$a} } keys %hash) { printf "%4d %s\n", $hash{$key}, $key; } -As an lvalue C allows you to increase the number of hash buckets +As an lvalue C allows you to increase the number of hash buckets allocated for the given hash. This can gain you a measure of efficiency if you know the hash is going to get big. (This is similar to pre-extending an array by assigning a larger number to $#array.) If you say keys %hash = 200; -then C<%hash> will have at least 200 buckets allocated for it. These +then C<%hash> will have at least 200 buckets allocated for it--256 of them, in fact, since +it rounds up to the next power of two. These buckets will be retained even if you do C<%hash = ()>, use C if you want to free the storage while C<%hash> is still in scope. You can't shrink the number of buckets allocated for the hash using -C in this way (but you needn't worry about doing this by accident, +C in this way (but you needn't worry about doing this by accident, as trying has no effect). =item kill LIST @@ -1739,40 +1931,43 @@ C block, if any, is not executed: LINE: while () { last LINE if /^$/; # exit when done with header - ... + #... } +See also L for an illustration of how C, C, and +C work. + =item lc EXPR =item lc Returns an lowercased version of EXPR. This is the internal function -implementing the \L escape in double-quoted strings. -Respects current LC_CTYPE locale if C in force. See L. +implementing the C<\L> escape in double-quoted strings. +Respects current C locale if C in force. See L. -If EXPR is omitted, uses $_. +If EXPR is omitted, uses C<$_>. =item lcfirst EXPR =item lcfirst Returns the value of EXPR with the first character lowercased. This is -the internal function implementing the \l escape in double-quoted strings. -Respects current LC_CTYPE locale if C in force. See L. +the internal function implementing the C<\l> escape in double-quoted strings. +Respects current C locale if C in force. See L. -If EXPR is omitted, uses $_. +If EXPR is omitted, uses C<$_>. =item length EXPR =item length -Returns the length in characters of the value of EXPR. If EXPR is -omitted, returns length of $_. +Returns the length in bytes of the value of EXPR. If EXPR is +omitted, returns length of C<$_>. =item link OLDFILE,NEWFILE -Creates a new filename linked to the old filename. Returns 1 for -success, 0 otherwise. +Creates a new filename linked to the old filename. Returns TRUE for +success, FALSE otherwise. =item listen SOCKET,QUEUESIZE @@ -1781,13 +1976,13 @@ it succeeded, FALSE otherwise. See example in L, or C. If more than one value is listed, the -list must be placed in parentheses. See L for details, including issues with tied arrays and hashes. +A local modifies the listed variables to be local to the enclosing +block, file, or eval. If more than one value is listed, the list must +be placed in parentheses. See L +for details, including issues with tied arrays and hashes. -But you really probably want to be using my() instead, because local() isn't -what most people think of as "local"). See L instead, because C isn't +what most people think of as "local". See L for details. =item localtime EXPR @@ -1801,27 +1996,35 @@ follows: localtime(time); All array elements are numeric, and come straight out of a struct tm. -In particular this means that $mon has the range 0..11 and $wday has -the range 0..6 with sunday as day 0. Also, $year is the number of -years since 1900, that is, $year is 123 in year 2023. +In particular this means that C<$mon> has the range C<0..11> and C<$wday> has +the range C<0..6> with sunday as day C<0>. Also, C<$year> is the number of +years since 1900, that is, C<$year> is C<123> in year 2023, and I simply the last two digits of the year. If EXPR is omitted, uses the current time (C). -In a scalar context, returns the ctime(3) value: +In scalar context, returns the ctime(3) value: $now_string = localtime; # e.g., "Thu Oct 13 04:54:34 1994" -This scalar value is B locale dependent, see L, -but instead a Perl builtin. -Also see the Time::Local module, and the strftime(3) and mktime(3) -function available via the POSIX module. +This scalar value is B locale dependent, see L, but +instead a Perl builtin. Also see the C module, and the +strftime(3) and mktime(3) function available via the POSIX module. To +get somewhat similar but locale dependent date strings, set up your +locale environment variables appropriately (please see L) +and try for example: + + use POSIX qw(strftime); + $now_string = strftime "%a %b %e %H:%M:%S %Y", localtime; + +Note that the C<%a> and C<%b>, the short forms of the day of the week +and the month of the year, may not necessarily be three characters wide. =item log EXPR =item log -Returns logarithm (base I) of EXPR. If EXPR is omitted, returns log -of $_. +Returns the natural logarithm (base I) of EXPR. If EXPR is omitted, returns log +of C<$_>. =item lstat FILEHANDLE @@ -1829,11 +2032,12 @@ of $_. =item lstat -Does the same thing as the stat() function, but stats a symbolic link -instead of the file the symbolic link points to. If symbolic links are -unimplemented on your system, a normal stat() is done. +Does the same thing as the C function (including setting the +special C<_> filehandle) but stats a symbolic link instead of the file +the symbolic link points to. If symbolic links are unimplemented on +your system, a normal C is done. -If EXPR is omitted, stats $_. +If EXPR is omitted, stats C<$_>. =item m// @@ -1843,7 +2047,7 @@ The match operator. See L. =item map EXPR,LIST -Evaluates the BLOCK or EXPR for each element of LIST (locally setting $_ to each +Evaluates the BLOCK or EXPR for each element of LIST (locally setting C<$_> to each element) and returns the list value composed of the results of each such evaluation. Evaluates BLOCK or EXPR in a list context, so each element of LIST may produce zero, one, or more elements in the returned value. @@ -1861,7 +2065,7 @@ is just a funny way to write $hash{getkey($_)} = $_; } -Note that, because $_ is a reference into the list value, it can be used +Note that, because C<$_> is a reference into the list value, it can be used to modify the elements of the array. While this is useful and supported, it can cause bizarre results if the LIST is not a named array. See also L for an array composed of those items of the @@ -1870,41 +2074,48 @@ original list for which the BLOCK or EXPR evaluates to true. =item mkdir FILENAME,MODE Creates the directory specified by FILENAME, with permissions specified -by MODE (as modified by umask). If it succeeds it returns 1, otherwise -it returns 0 and sets C<$!> (errno). +by MODE (as modified by umask). If it succeeds it returns TRUE, otherwise +it returns FALSE and sets C<$!> (errno). =item msgctl ID,CMD,ARG -Calls the System V IPC function msgctl(2). If CMD is &IPC_STAT, then ARG -must be a variable which will hold the returned msqid_ds structure. -Returns like ioctl: the undefined value for error, "0 but true" for -zero, or the actual return value otherwise. +Calls the System V IPC function msgctl(2). You'll probably have to say + + use IPC::SysV; + +first to get the correct constant definitions. If CMD is C, +then ARG must be a variable which will hold the returned C +structure. Returns like C: the undefined value for error, "C<0> but +true" for zero, or the actual return value otherwise. See also +C and C documentation. =item msgget KEY,FLAGS -Calls the System V IPC function msgget(2). Returns the message queue id, -or the undefined value if there is an error. +Calls the System V IPC function msgget(2). Returns the message queue +id, or the undefined value if there is an error. See also C +and C documentation. =item msgsnd ID,MSG,FLAGS Calls the System V IPC function msgsnd to send the message MSG to the message queue ID. MSG must begin with the long integer message type, which may be created with C. Returns TRUE if -successful, or FALSE if there is an error. +successful, or FALSE if there is an error. See also C +and C documentation. =item msgrcv ID,VAR,SIZE,TYPE,FLAGS Calls the System V IPC function msgrcv to receive a message from message queue ID into variable VAR with a maximum message size of -SIZE. Note that if a message is received, the message type will be the -first thing in VAR, and the maximum length of VAR is SIZE plus the size -of the message type. Returns TRUE if successful, or FALSE if there is -an error. +SIZE. Note that if a message is received, the message type will be +the first thing in VAR, and the maximum length of VAR is SIZE plus the +size of the message type. Returns TRUE if successful, or FALSE if +there is an error. See also C and C documentation. =item my EXPR -A "my" declares the listed variables to be local (lexically) to the -enclosing block, subroutine, C, or C'd file. If +A C declares the listed variables to be local (lexically) to the +enclosing block, file, or C. If more than one value is listed, the list must be placed in parentheses. See L for details. @@ -1917,30 +2128,33 @@ the next iteration of the loop: LINE: while () { next LINE if /^#/; # discard comments - ... + #... } Note that if there were a C block on the above, it would get executed even on discarded lines. If the LABEL is omitted, the command refers to the innermost enclosing loop. +See also L for an illustration of how C, C, and +C work. + =item no Module LIST -See the "use" function, which "no" is the opposite of. +See the L function, which C is the opposite of. =item oct EXPR =item oct Interprets EXPR as an octal string and returns the corresponding -value. (If EXPR happens to start off with 0x, interprets it as +value. (If EXPR happens to start off with C<0x>, interprets it as a hex string instead.) The following will handle decimal, octal, and hex in the standard Perl or C notation: $val = oct($val) if $val =~ /^0/; -If EXPR is omitted, uses $_. This function is commonly used when -a string such as "644" needs to be converted into a file mode, for +If EXPR is omitted, uses C<$_>. This function is commonly used when +a string such as C<644> needs to be converted into a file mode, for example. (Although perl will automatically convert strings into numbers as needed, this automatic conversion assumes base 10.) @@ -1952,46 +2166,50 @@ Opens the file whose filename is given by EXPR, and associates it with FILEHANDLE. If FILEHANDLE is an expression, its value is used as the name of the real filehandle wanted. If EXPR is omitted, the scalar variable of the same name as the FILEHANDLE contains the filename. -(Note that lexical variables--those declared with C--will not work -for this purpose; so if you're using C, specify EXPR in your call +(Note that lexical variables--those declared with C--will not work +for this purpose; so if you're using C, specify EXPR in your call to open.) -If the filename begins with '<' or nothing, the file is opened for input. -If the filename begins with '>', the file is truncated and opened for -output. If the filename begins with '>>', the file is opened for -appending. You can put a '+' in front of the '>' or '<' to indicate that -you want both read and write access to the file; thus '+<' is almost -always preferred for read/write updates--the '+>' mode would clobber the -file first. The prefix and the filename may be separated with spaces. -These various prefixes correspond to the fopen(3) modes of 'r', 'r+', 'w', -'w+', 'a', and 'a+'. - -If the filename begins with "|", the filename is interpreted as a command -to which output is to be piped, and if the filename ends with a "|", the -filename is interpreted See L for more -examples of this. as command which pipes input to us. (You may not have -a raw open() to a command that pipes both in I out, but see -L, L, and L -for alternatives.) - -Opening '-' opens STDIN and opening 'E-' opens STDOUT. Open returns -nonzero upon success, the undefined value otherwise. If the open +If the filename begins with C<'E'> or nothing, the file is opened for input. +If the filename begins with C<'E'>, the file is truncated and opened for +output, being created if necessary. If the filename begins with C<'EE'>, +the file is opened for appending, again being created if necessary. +You can put a C<'+'> in front of the C<'E'> or C<'E'> to indicate that +you want both read and write access to the file; thus C<'+E'> is almost +always preferred for read/write updates--the C<'+E'> mode would clobber the +file first. You can't usually use either read-write mode for updating +textfiles, since they have variable length records. See the B<-i> +switch in L for a better approach. + +The prefix and the filename may be separated with spaces. +These various prefixes correspond to the fopen(3) modes of C<'r'>, C<'r+'>, C<'w'>, +C<'w+'>, C<'a'>, and C<'a+'>. + +If the filename begins with C<'|'>, the filename is interpreted as a +command to which output is to be piped, and if the filename ends with a +C<'|'>, the filename is interpreted See L +for more examples of this. (You are not allowed to C to a command +that pipes both in I out, but see L, L, +and L for alternatives.) + +Opening C<'-'> opens STDIN and opening C<'E-'> opens STDOUT. Open returns +nonzero upon success, the undefined value otherwise. If the C involved a pipe, the return value happens to be the pid of the subprocess. If you're unfortunate enough to be running Perl on a system that distinguishes between text files and binary files (modern operating systems don't care), then you should check out L for tips for -dealing with this. The key distinction between systems that need binmode -and those that don't is their text file formats. Systems like Unix and -Plan9 that delimit lines with a single character, and that encode that -character in C as '\n', do not need C. The rest need it. +dealing with this. The key distinction between systems that need C +and those that don't is their text file formats. Systems like Unix, MacOS, and +Plan9, which delimit lines with a single character, and which encode that +character in C as C<"\n">, do not need C. The rest need it. When opening a file, it's usually a bad idea to continue normal execution -if the request failed, so C is frequently used in connection with -C. Even if C won't do what you want (say, in a CGI script, +if the request failed, so C is frequently used in connection with +C. Even if C won't do what you want (say, in a CGI script, where you want to make a nicely formatted error message (but there are -modules which can help with that problem)) you should always check +modules that can help with that problem)) you should always check the return value from opening a file. The infrequent exception is when working with an unopened filehandle is actually what you want to do. @@ -2020,27 +2238,28 @@ Examples: } sub process { - local($filename, $input) = @_; + my($filename, $input) = @_; $input++; # this is a string increment unless (open($input, $filename)) { print STDERR "Can't open $filename: $!\n"; return; } + local $_; while (<$input>) { # note use of indirection if (/^#include "(.*)"/) { process($1, $input); next; } - ... # whatever + #... # whatever } } You may also, in the Bourne shell tradition, specify an EXPR beginning -with "E&", in which case the rest of the string is interpreted as the -name of a filehandle (or file descriptor, if numeric) which is to be -duped and opened. You may use & after E, EE, E, +E, -+EE, and +E. The +with C<'E&'>, in which case the rest of the string is interpreted as the +name of a filehandle (or file descriptor, if numeric) to be +duped and opened. You may use C<&> after C>, CE>, C>, C<+E>, +C<+EE>, and C<+E>. The mode you specify should match the mode of the original filehandle. (Duping a filehandle does not take into account any existing contents of stdio buffers.) @@ -2048,8 +2267,8 @@ Here is a script that saves, redirects, and restores STDOUT and STDERR: #!/usr/bin/perl - open(SAVEOUT, ">&STDOUT"); - open(SAVEERR, ">&STDERR"); + open(OLDOUT, ">&STDOUT"); + open(OLDERR, ">&STDERR"); open(STDOUT, ">foo.out") || die "Can't redirect stdout"; open(STDERR, ">&STDOUT") || die "Can't dup stdout"; @@ -2063,22 +2282,22 @@ STDERR: close(STDOUT); close(STDERR); - open(STDOUT, ">&SAVEOUT"); - open(STDERR, ">&SAVEERR"); + open(STDOUT, ">&OLDOUT"); + open(STDERR, ">&OLDERR"); print STDOUT "stdout 2\n"; print STDERR "stderr 2\n"; -If you specify "E&=N", where N is a number, then Perl will do an -equivalent of C's fdopen() of that file descriptor; this is more +If you specify C<'E&=N'>, where C is a number, then Perl will do an +equivalent of C's C of that file descriptor; this is more parsimonious of file descriptors. For example: open(FILEHANDLE, "<&=$fd") -If you open a pipe on the command "-", i.e., either "|-" or "-|", then +If you open a pipe on the command C<'-'>, i.e., either C<'|-'> or C<'-|'>, then there is an implicit fork done, and the return value of open is the pid -of the child within the parent process, and 0 within the child +of the child within the parent process, and C<0> within the child process. (Use C to determine whether the open was successful.) The filehandle behaves normally for the parent, but i/o to that filehandle is piped from/to the STDOUT/STDIN of the child process. @@ -2097,21 +2316,47 @@ The following pairs are more or less equivalent: See L for more examples of this. -NOTE: On any operation which may do a fork, unflushed buffers remain +NOTE: On any operation that may do a fork, any unflushed buffers remain unflushed in both processes, which means you may need to set C<$|> to avoid duplicate output. Closing any piped filehandle causes the parent process to wait for the child to finish, and returns the status value in C<$?>. -Using the constructor from the IO::Handle package (or one of its -subclasses, such as IO::File or IO::Socket), -you can generate anonymous filehandles which have the scope of whatever -variables hold references to them, and automatically close whenever -and however you leave that scope: +The filename passed to open will have leading and trailing +whitespace deleted, and the normal redirection characters +honored. This property, known as "magic open", +can often be used to good effect. A user could specify a filename of +F<"rsh cat file |">, or you could change certain filenames as needed: + + $filename =~ s/(.*\.gz)\s*$/gzip -dc < $1|/; + open(FH, $filename) or die "Can't open $filename: $!"; + +However, to open a file with arbitrary weird characters in it, it's +necessary to protect any leading and trailing whitespace: + + $file =~ s#^(\s)#./$1#; + open(FOO, "< $file\0"); + +If you want a "real" C C (see L on your system), then you +should use the C function, which involves no such magic. This is +another way to protect your filenames from interpretation. For example: + + use IO::Handle; + sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL) + or die "sysopen $path: $!"; + $oldfh = select(HANDLE); $| = 1; select($oldfh); + print HANDLE "stuff $$\n"); + seek(HANDLE, 0, 0); + print "File contains: ", ; + +Using the constructor from the C package (or one of its +subclasses, such as C or C), you can generate anonymous +filehandles that have the scope of whatever variables hold references to +them, and automatically close whenever and however you leave that scope: use IO::File; - ... + #... sub read_myfile_munged { my $ALL = shift; my $handle = new IO::File; @@ -2123,32 +2368,12 @@ and however you leave that scope: $first; # Or here. } -The filename that is passed to open will have leading and trailing -whitespace deleted. To open a file with arbitrary weird -characters in it, it's necessary to protect any leading and trailing -whitespace thusly: - - $file =~ s#^(\s)#./$1#; - open(FOO, "< $file\0"); - -If you want a "real" C open() (see L on your system), then -you should use the sysopen() function. This is another way to -protect your filenames from interpretation. For example: - - use IO::Handle; - sysopen(HANDLE, $path, O_RDWR|O_CREAT|O_EXCL, 0700) - or die "sysopen $path: $!"; - HANDLE->autoflush(1); - HANDLE->print("stuff $$\n"); - seek(HANDLE, 0, 0); - print "File contains: ", ; - See L for some details about mixing reading and writing. =item opendir DIRHANDLE,EXPR -Opens a directory named EXPR for processing by readdir(), telldir(), -seekdir(), rewinddir(), and closedir(). Returns TRUE if successful. +Opens a directory named EXPR for processing by C, C, +C, C, and C. Returns TRUE if successful. DIRHANDLEs have their own namespace separate from FILEHANDLEs. =item ord EXPR @@ -2156,7 +2381,7 @@ DIRHANDLEs have their own namespace separate from FILEHANDLEs. =item ord Returns the numeric ascii value of the first character of EXPR. If -EXPR is omitted, uses $_. For the reverse, see L. +EXPR is omitted, uses C<$_>. For the reverse, see L. =item pack TEMPLATE,LIST @@ -2182,9 +2407,10 @@ follows: i A signed integer value. I An unsigned integer value. - (This 'integer' is _at_least_ 32 bits wide. Its exact size - depends on what a local C compiler calls 'int', and may - even be larger than the 'long' described in the next item.) + (This 'integer' is _at_least_ 32 bits wide. Its exact + size depends on what a local C compiler calls 'int', + and may even be larger than the 'long' described in + the next item.) l A signed long value. L An unsigned long value. @@ -2207,28 +2433,28 @@ follows: u A uuencoded string. w A BER compressed integer. Its bytes represent an unsigned - integer in base 128, most significant digit first, with as few - digits as possible. Bit eight (the high bit) is set on each - byte except the last. + integer in base 128, most significant digit first, with as + few digits as possible. Bit eight (the high bit) is set + on each byte except the last. x A null byte. X Back up a byte. @ Null fill to absolute position. -Each letter may optionally be followed by a number which gives a repeat -count. With all types except "a", "A", "b", "B", "h", "H", and "P" the -pack function will gobble up that many values from the LIST. A * for the -repeat count means to use however many items are left. The "a" and "A" +Each letter may optionally be followed by a number giving a repeat +count. With all types except C<"a">, C<"A">, C<"b">, C<"B">, C<"h">, C<"H">, and C<"P"> the +pack function will gobble up that many values from the LIST. A C<*> for the +repeat count means to use however many items are left. The C<"a"> and C<"A"> types gobble just one value, but pack it as a string of length count, -padding with nulls or spaces as necessary. (When unpacking, "A" strips -trailing spaces and nulls, but "a" does not.) Likewise, the "b" and "B" -fields pack a string that many bits long. The "h" and "H" fields pack a -string that many nybbles long. The "p" type packs a pointer to a null- +padding with nulls or spaces as necessary. (When unpacking, C<"A"> strips +trailing spaces and nulls, but C<"a"> does not.) Likewise, the C<"b"> and C<"B"> +fields pack a string that many bits long. The C<"h"> and C<"H"> fields pack a +string that many nybbles long. The C<"p"> type packs a pointer to a null- terminated string. You are responsible for ensuring the string is not a temporary value (which can potentially get deallocated before you get -around to using the packed result). The "P" packs a pointer to a structure +around to using the packed result). The C<"P"> packs a pointer to a structure of the size indicated by the length. A NULL pointer is created if the -corresponding value for "p" or "P" is C. +corresponding value for C<"p"> or C<"P"> is C. Real numbers (floats and doubles) are in the native machine format only; due to the multiplicity of floating formats around, and the lack of a standard "network" representation, no @@ -2238,7 +2464,7 @@ both use IEEE floating point arithmetic (as the endian-ness of the memory representation is not part of the IEEE spec). Note that Perl uses doubles internally for all numeric calculation, and converting from double into float and thence back to double again will lose precision (i.e., -C) will not in general equal $foo). +C) will not in general equal C<$foo>). Examples: @@ -2272,22 +2498,28 @@ Examples: The same template may generally also be used in the unpack function. +=item package + =item package NAMESPACE Declares the compilation unit as being in the given namespace. The scope of the package declaration is from the declaration itself through the end of -the enclosing block (the same scope as the local() operator). All further +the enclosing block (the same scope as the C operator). All further unqualified dynamic identifiers will be in this namespace. A package statement affects only dynamic variables--including those you've used -local() on--but I lexical variables created with my(). Typically it +C on--but I lexical variables created with C. Typically it would be the first declaration in a file to be included by the C or C operator. You can switch into a package in more than one place; -it influences merely which symbol table is used by the compiler for the +it merely influences which symbol table is used by the compiler for the rest of that block. You can refer to variables and filehandles in other packages by prefixing the identifier with the package name and a double colon: C<$Package::Variable>. If the package name is null, the C
package as assumed. That is, C<$::sail> is equivalent to C<$main::sail>. +If NAMESPACE is omitted, then there is no current package, and all +identifiers must be fully qualified or lexicals. This is stricter +than C, since it also extends to function names. + See L for more information about packages, modules, and classes. See L for other scoping issues. @@ -2313,15 +2545,15 @@ Pops and returns the last value of the array, shortening the array by If there are no elements in the array, returns the undefined value. If ARRAY is omitted, pops the -@ARGV array in the main program, and the @_ array in subroutines, just -like shift(). +C<@ARGV> array in the main program, and the C<@_> array in subroutines, just +like C. =item pos SCALAR =item pos Returns the offset of where the last C search left off for the variable -is in question ($_ is used when the variable is not specified). May be +is in question (C<$_> is used when the variable is not specified). May be modified to change that offset. Such modification will also influence the C<\G> zero-width assertion in regular expressions. See L and L. @@ -2337,16 +2569,16 @@ if successful. FILEHANDLE may be a scalar variable name, in which case the variable contains the name of or a reference to the filehandle, thus introducing one level of indirection. (NOTE: If FILEHANDLE is a variable and the next token is a term, it may be misinterpreted as an operator unless you -interpose a + or put parentheses around the arguments.) If FILEHANDLE is +interpose a C<+> or put parentheses around the arguments.) If FILEHANDLE is omitted, prints by default to standard output (or to the last selected -output channel--see L). If LIST is also omitted, prints $_ to -STDOUT. To set the default output channel to something other than +output channel--see L). If LIST is also omitted, prints C<$_> to +the currently selected output channel. To set the default output channel to something other than STDOUT use the select operation. Note that, because print takes a -LIST, anything in the LIST is evaluated in a list context, and any +LIST, anything in the LIST is evaluated in list context, and any subroutine that you call will have one or more of its expressions -evaluated in a list context. Also be careful not to follow the print +evaluated in list context. Also be careful not to follow the print keyword with a left parenthesis unless you want the corresponding right -parenthesis to terminate the arguments to the print--interpose a + or +parenthesis to terminate the arguments to the print--interpose a C<+> or put parentheses around all the arguments. Note that if you're storing FILEHANDLES in an array or other expression, @@ -2359,13 +2591,14 @@ you will have to use a block returning its value instead: =item printf FORMAT, LIST -Equivalent to C. The first argument -of the list will be interpreted as the printf format. If C is +Equivalent to C, except that C<$\> +(the output record separator) is not appended. The first argument +of the list will be interpreted as the C format. If C is in effect, the character used for the decimal point in formatted real numbers is affected by the LC_NUMERIC locale. See L. -Don't fall into the trap of using a printf() when a simple -print() would do. The print() is more efficient, and less +Don't fall into the trap of using a C when a simple +C would do. The C is more efficient and less error prone. =item prototype FUNCTION @@ -2376,8 +2609,8 @@ the function whose prototype you want to retrieve. If FUNCTION is a string starting with C, the rest is taken as a name for Perl builtin. If builtin is not I (such as -C) or its arguments cannot be expressed by a prototype (such as -C) - in other words, the builtin does not behave like a Perl +C) or its arguments cannot be expressed by a prototype (such as +C) - in other words, the builtin does not behave like a Perl function - returns C. Otherwise, the string describing the equivalent prototype is returned. @@ -2397,6 +2630,8 @@ but is more efficient. Returns the new number of elements in the array. =item qq/STRING/ +=item qr/STRING/ + =item qx/STRING/ =item qw/STRING/ @@ -2412,18 +2647,18 @@ characters backslashed. (That is, all characters not matching C will be preceded by a backslash in the returned string, regardless of any locale settings.) This is the internal function implementing -the \Q escape in double-quoted strings. +the C<\Q> escape in double-quoted strings. -If EXPR is omitted, uses $_. +If EXPR is omitted, uses C<$_>. =item rand EXPR =item rand -Returns a random fractional number greater than or equal to 0 and less +Returns a random fractional number greater than or equal to C<0> and less than the value of EXPR. (EXPR should be positive.) If EXPR is -omitted, the value 1 is used. Automatically calls srand() unless -srand() has already been called. See also srand(). +omitted, the value C<1> is used. Automatically calls C unless +C has already been called. See also C. (Note: If your rand function consistently returns numbers that are too large or too small, then your version of Perl was probably compiled @@ -2434,23 +2669,23 @@ with the wrong number of RANDBITS.) =item read FILEHANDLE,SCALAR,LENGTH Attempts to read LENGTH bytes of data into variable SCALAR from the -specified FILEHANDLE. Returns the number of bytes actually read, or -undef if there was an error. SCALAR will be grown or shrunk to the -length actually read. An OFFSET may be specified to place the read -data at some other place than the beginning of the string. This call -is actually implemented in terms of stdio's fread call. To get a true -read system call, see sysread(). +specified FILEHANDLE. Returns the number of bytes actually read, +C<0> at end of file, or undef if there was an error. SCALAR will be grown +or shrunk to the length actually read. An OFFSET may be specified to +place the read data at some other place than the beginning of the +string. This call is actually implemented in terms of stdio's fread(3) +call. To get a true read(2) system call, see C. =item readdir DIRHANDLE -Returns the next directory entry for a directory opened by opendir(). -If used in a list context, returns all the rest of the entries in the +Returns the next directory entry for a directory opened by C. +If used in list context, returns all the rest of the entries in the directory. If there are no more entries, returns an undefined value in -a scalar context or a null list in a list context. +scalar context or a null list in list context. -If you're planning to filetest the return values out of a readdir(), you'd +If you're planning to filetest the return values out of a C, you'd better prepend the directory in question. Otherwise, because we didn't -chdir() there, it would have been testing the wrong file. +C there, it would have been testing the wrong file. opendir(DIR, $some_dir) || die "can't opendir $some_dir: $!"; @dots = grep { /^\./ && -f "$some_dir/$_" } readdir(DIR); @@ -2458,14 +2693,17 @@ chdir() there, it would have been testing the wrong file. =item readline EXPR -Reads from the file handle EXPR. In scalar context, a single line +Reads from the filehandle whose typeglob is contained in EXPR. In scalar context, a single line is read and returned. In list context, reads until end-of-file is reached and returns a list of lines (however you've defined lines -with $/ or $INPUT_RECORD_SEPARATOR). +with C<$/> or C<$INPUT_RECORD_SEPARATOR>). This is the internal function implementing the CEXPRE> operator, but you can use it directly. The CEXPRE> operator is discussed in more detail in L. + $line = ; + $line = readline(*STDIN); # same thing + =item readlink EXPR =item readlink @@ -2473,15 +2711,15 @@ operator is discussed in more detail in L. Returns the value of a symbolic link, if symbolic links are implemented. If not, gives a fatal error. If there is some system error, returns the undefined value and sets C<$!> (errno). If EXPR is -omitted, uses $_. +omitted, uses C<$_>. =item readpipe EXPR -EXPR is interpolated and then executed as a system command. +EXPR is executed as a system command. The collected standard output of the command is returned. In scalar context, it comes back as a single (potentially multi-line) string. In list context, returns a list of lines -(however you've defined lines with $/ or $INPUT_RECORD_SEPARATOR). +(however you've defined lines with C<$/> or C<$INPUT_RECORD_SEPARATOR>). This is the internal function implementing the C operator, but you can use it directly. The C operator is discussed in more detail in L. @@ -2490,7 +2728,7 @@ operator is discussed in more detail in L. Receives a message on a socket. Attempts to receive LENGTH bytes of data into variable SCALAR from the specified SOCKET filehandle. -Actually does a C recvfrom(), so that it can returns the address of the +Actually does a C C, so that it can return the address of the sender. Returns the undefined value if there's an error. SCALAR will be grown or shrunk to the length actually read. Takes the same flags as the system call of the same name. @@ -2515,7 +2753,7 @@ themselves about what was just input: $front = $_; while () { if (/}/) { # end of comment? - s|^|$front{|; + s|^|$front\{|; redo LINE; } } @@ -2523,12 +2761,15 @@ themselves about what was just input: print; } +See also L for an illustration of how C, C, and +C work. + =item ref EXPR =item ref Returns a TRUE value if EXPR is a reference, FALSE otherwise. If EXPR -is not specified, $_ will be used. The value returned depends on the +is not specified, C<$_> will be used. The value returned depends on the type of thing the reference is a reference to. Builtin types include: @@ -2540,12 +2781,12 @@ Builtin types include: GLOB If the referenced object has been blessed into a package, then that package -name is returned instead. You can think of ref() as a typeof() operator. +name is returned instead. You can think of C as a C operator. if (ref($r) eq "HASH") { print "r is a reference to a hash.\n"; } - if (!ref ($r) { + if (!ref($r)) { print "r is not a reference at all.\n"; } @@ -2553,26 +2794,26 @@ See also L. =item rename OLDNAME,NEWNAME -Changes the name of a file. Returns 1 for success, 0 otherwise. Will +Changes the name of a file. Returns C<1> for success, C<0> otherwise. Will not work across file system boundaries. =item require EXPR =item require -Demands some semantics specified by EXPR, or by $_ if EXPR is not +Demands some semantics specified by EXPR, or by C<$_> if EXPR is not supplied. If EXPR is numeric, demands that the current version of Perl (C<$]> or $PERL_VERSION) be equal or greater than EXPR. Otherwise, demands that a library file be included if it hasn't already been included. The file is included via the do-FILE mechanism, which is -essentially just a variety of eval(). Has semantics similar to the following +essentially just a variety of C. Has semantics similar to the following subroutine: sub require { - local($filename) = @_; + my($filename) = @_; return 1 if $INC{$filename}; - local($realfilename,$result); + my($realfilename,$result); ITER: { foreach $prefix (@INC) { $realfilename = "$prefix/$filename"; @@ -2586,13 +2827,13 @@ subroutine: die $@ if $@; die "$filename did not return true value" unless $result; $INC{$filename} = $realfilename; - $result; + return $result; } Note that the file will not be included twice under the same specified name. The file must return TRUE as the last statement to indicate successful execution of any initialization code, so it's customary to -end such a file with "1;" unless you're sure it'll return TRUE +end such a file with "C<1;>" unless you're sure it'll return TRUE otherwise. But it's better just to put the "C<1;>", in case you add more statements. @@ -2601,19 +2842,37 @@ replaces "F<::>" with "F" in the filename for you, to make it easy to load standard modules. This form of loading of modules does not risk altering your namespace. -For a yet-more-powerful import facility, see L and -L. +In other words, if you try this: + + require Foo::Bar; # a splendid bareword + +The require function will actually look for the "F" file in the +directories specified in the C<@INC> array. + +But if you try this: + + $class = 'Foo::Bar'; + require $class; # $class is not a bareword + #or + require "Foo::Bar"; # not a bareword because of the "" + +The require function will look for the "F" file in the @INC array and +will complain about not finding "F" there. In this case you can do: + + eval "require $class"; + +For a yet-more-powerful import facility, see L and L. =item reset EXPR =item reset Generally used in a C block at the end of a loop to clear -variables and reset ?? searches so that they work again. The +variables and reset C searches so that they work again. The expression is interpreted as a list of single characters (hyphens allowed for ranges). All variables and arrays beginning with one of those letters are reset to their pristine state. If the expression is -omitted, one-match searches (?pattern?) are reset to match again. Resets +omitted, one-match searches (C) are reset to match again. Resets only variables or searches in the current package. Always returns 1. Examples: @@ -2621,8 +2880,8 @@ only variables or searches in the current package. Always returns reset 'a-z'; # reset lower case variables reset; # just reset ?? searches -Resetting "A-Z" is not recommended because you'll wipe out your -ARGV and ENV arrays. Resets only package variables--lexical variables +Resetting C<"A-Z"> is not recommended because you'll wipe out your +C<@ARGV> and C<@INC> arrays and your C<%ENV> hash. Resets only package variables--lexical variables are unaffected, but they clean themselves up on scope exit anyway, so you'll probably want to use them instead. See L. @@ -2630,20 +2889,20 @@ so you'll probably want to use them instead. See L. =item return -Returns from a subroutine, eval(), or do FILE with the value of the -given EXPR. Evaluation of EXPR may be in a list, scalar, or void +Returns from a subroutine, C, or C with the value +given in EXPR. Evaluation of EXPR may be in list, scalar, or void context, depending on how the return value will be used, and the context -may vary from one execution to the next (see wantarray()). If no EXPR -is given, returns an empty list in a list context, an undefined value in -a scalar context, or nothing in a void context. +may vary from one execution to the next (see C). If no EXPR +is given, returns an empty list in list context, an undefined value in +scalar context, or nothing in a void context. (Note that in the absence of a return, a subroutine, eval, or do FILE will automatically return the value of the last expression evaluated.) =item reverse LIST -In a list context, returns a list value consisting of the elements -of LIST in the opposite order. In a scalar context, concatenates the +In list context, returns a list value consisting of the elements +of LIST in the opposite order. In scalar context, concatenates the elements of LIST, and returns a string value consisting of those bytes, but in the opposite order. @@ -2663,7 +2922,7 @@ on a large hash. =item rewinddir DIRHANDLE Sets the current position to the beginning of the directory for the -readdir() routine on DIRHANDLE. +C routine on DIRHANDLE. =item rindex STR,SUBSTR,POSITION @@ -2677,9 +2936,9 @@ last occurrence at or before that position. =item rmdir -Deletes the directory specified by FILENAME if it is empty. If it -succeeds it returns 1, otherwise it returns 0 and sets C<$!> (errno). If -FILENAME is omitted, uses $_. +Deletes the directory specified by FILENAME if that directory is empty. If it +succeeds it returns TRUE, otherwise it returns FALSE and sets C<$!> (errno). If +FILENAME is omitted, uses C<$_>. =item s/// @@ -2687,41 +2946,41 @@ The substitution operator. See L. =item scalar EXPR -Forces EXPR to be interpreted in a scalar context and returns the value +Forces EXPR to be interpreted in scalar context and returns the value of EXPR. @counts = ( scalar @a, scalar @b, scalar @c ); There is no equivalent operator to force an expression to -be interpolated in a list context because it's in practice never +be interpolated in list context because it's in practice never needed. If you really wanted to do so, however, you could use the construction C<@{[ (some expression) ]}>, but usually a simple C<(some expression)> suffices. =item seek FILEHANDLE,POSITION,WHENCE -Sets FILEHANDLE's position, just like the fseek() call of stdio. +Sets FILEHANDLE's position, just like the C call of C. FILEHANDLE may be an expression whose value gives the name of the -filehandle. The values for WHENCE are 0 to set the new position to -POSITION, 1 to set it to the current position plus POSITION, and 2 to +filehandle. The values for WHENCE are C<0> to set the new position to +POSITION, C<1> to set it to the current position plus POSITION, and C<2> to set it to EOF plus POSITION (typically negative). For WHENCE you may -use the constants SEEK_SET, SEEK_CUR, and SEEK_END from either the -IO::Seekable or the POSIX module. Returns 1 upon success, 0 otherwise. +use the constants C, C, and C from either the +C or the POSIX module. Returns C<1> upon success, C<0> otherwise. -If you want to position file for sysread() or syswrite(), don't use -seek() -- buffering makes its effect on the file's system position -unpredictable and non-portable. Use sysseek() instead. +If you want to position file for C or C, don't use +C -- buffering makes its effect on the file's system position +unpredictable and non-portable. Use C instead. On some systems you have to do a seek whenever you switch between reading and writing. Amongst other things, this may have the effect of calling -stdio's clearerr(3). A WHENCE of 1 (SEEK_CUR) is useful for not moving +stdio's clearerr(3). A WHENCE of C<1> (C) is useful for not moving the file position: seek(TEST,0,1); This is also useful for applications emulating C. Once you hit EOF on your read, and then sleep for a while, you might have to stick in a -seek() to reset things. The seek() doesn't change the current position, +seek() to reset things. The C doesn't change the current position, but it I clear the end-of-file condition on the handle, so that the next CFILEE> makes Perl try again to read something. We hope. @@ -2729,7 +2988,8 @@ If that doesn't work (some stdios are particularly cantankerous), then you may need something more like this: for (;;) { - for ($curpos = tell(FILE); $_ = ; $curpos = tell(FILE)) { + for ($curpos = tell(FILE); $_ = ; + $curpos = tell(FILE)) { # search for some stuff and put it into files } sleep($for_a_while); @@ -2738,8 +2998,8 @@ you may need something more like this: =item seekdir DIRHANDLE,POS -Sets the current position for the readdir() routine on DIRHANDLE. POS -must be a value returned by telldir(). Has the same caveats about +Sets the current position for the C routine on DIRHANDLE. POS +must be a value returned by C. Has the same caveats about possible directory compaction as the corresponding system library routine. @@ -2749,7 +3009,7 @@ routine. Returns the currently selected filehandle. Sets the current default filehandle for output, if FILEHANDLE is supplied. This has two -effects: first, a C or a C without a filehandle will +effects: first, a C or a C without a filehandle will default to this FILEHANDLE. Second, references to variables related to output will refer to this output channel. For example, if you have to set the top of form format for more than one output channel, you might @@ -2774,7 +3034,7 @@ methods, preferring to write the last example as: =item select RBITS,WBITS,EBITS,TIMEOUT This calls the select(2) system call with the bit masks specified, which -can be constructed using fileno() and vec(), along these lines: +can be constructed using C and C, along these lines: $rin = $win = $ein = ''; vec($rin,fileno(STDIN),1) = 1; @@ -2785,8 +3045,8 @@ If you want to select on many filehandles you might wish to write a subroutine: sub fhbits { - local(@fhlist) = split(' ',$_[0]); - local($bits); + my(@fhlist) = split(' ',$_[0]); + my($bits); for (@fhlist) { vec($bits,fileno($_),1) = 1; } @@ -2803,33 +3063,39 @@ or to block until something becomes ready just do this $nfound = select($rout=$rin, $wout=$win, $eout=$ein, undef); -Most systems do not bother to return anything useful in $timeleft, so -calling select() in a scalar context just returns $nfound. +Most systems do not bother to return anything useful in C<$timeleft>, so +calling select() in scalar context just returns C<$nfound>. Any of the bit masks can also be undef. The timeout, if specified, is in seconds, which may be fractional. Note: not all implementations are -capable of returning the $timeleft. If not, they always return -$timeleft equal to the supplied $timeout. +capable of returning theC<$timeleft>. If not, they always return +C<$timeleft> equal to the supplied C<$timeout>. You can effect a sleep of 250 milliseconds this way: select(undef, undef, undef, 0.25); -B: Do not attempt to mix buffered I/O (like read() or EFHE) -with select(). You have to use sysread() instead. +B: One should not attempt to mix buffered I/O (like C +or EFHE) with C, except as permitted by POSIX, and even +then only on POSIX systems. You have to use C instead. =item semctl ID,SEMNUM,CMD,ARG -Calls the System V IPC function semctl. If CMD is &IPC_STAT or -&GETALL, then ARG must be a variable which will hold the returned -semid_ds structure or semaphore value array. Returns like ioctl: the -undefined value for error, "0 but true" for zero, or the actual return -value otherwise. +Calls the System V IPC function C. You'll probably have to say + + use IPC::SysV; + +first to get the correct constant definitions. If CMD is IPC_STAT or +GETALL, then ARG must be a variable which will hold the returned +semid_ds structure or semaphore value array. Returns like C: the +undefined value for error, "C<0> but true" for zero, or the actual return +value otherwise. See also C and C documentation. =item semget KEY,NSEMS,FLAGS Calls the System V IPC function semget. Returns the semaphore id, or -the undefined value if there is an error. +the undefined value if there is an error. See also C and +C documentation. =item semop KEY,OPSTRING @@ -2839,12 +3105,13 @@ semop structures. Each semop structure can be generated with C. The number of semaphore operations is implied by the length of OPSTRING. Returns TRUE if successful, or FALSE if there is an error. As an example, the -following code waits on semaphore $semnum of semaphore id $semid: +following code waits on semaphore C<$semnum> of semaphore id C<$semid>: $semop = pack("sss", $semnum, -1, 0); die "Semaphore trouble: $!\n" unless semop($semid, $semop); -To signal the semaphore, replace "-1" with "1". +To signal the semaphore, replace C<-1> with C<1>. See also C +and C documentation. =item send SOCKET,MSG,FLAGS,TO @@ -2852,18 +3119,18 @@ To signal the semaphore, replace "-1" with "1". Sends a message on a socket. Takes the same flags as the system call of the same name. On unconnected sockets you must specify a -destination to send TO, in which case it does a C sendto(). Returns +destination to send TO, in which case it does a C C. Returns the number of characters sent, or the undefined value if there is an error. See L for examples. =item setpgrp PID,PGRP -Sets the current process group for the specified PID, 0 for the current +Sets the current process group for the specified PID, C<0> for the current process. Will produce a fatal error if used on a machine that doesn't implement setpgrp(2). If the arguments are omitted, it defaults to -0,0. Note that the POSIX version of setpgrp() does not accept any -arguments, so only setpgrp 0,0 is portable. +C<0,0>. Note that the POSIX version of C does not accept any +arguments, so only setpgrp C<0,0> is portable. =item setpriority WHICH,WHO,PRIORITY @@ -2874,7 +3141,7 @@ that doesn't implement setpriority(2). =item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL Sets the socket option requested. Returns undefined if there is an -error. OPTVAL may be specified as undef if you don't want to pass an +error. OPTVAL may be specified as C if you don't want to pass an argument. =item shift ARRAY @@ -2884,24 +3151,30 @@ argument. Shifts the first value of the array off and returns it, shortening the array by 1 and moving everything down. If there are no elements in the array, returns the undefined value. If ARRAY is omitted, shifts the -@_ array within the lexical scope of subroutines and formats, and the -@ARGV array at file scopes or within the lexical scopes established by +C<@_> array within the lexical scope of subroutines and formats, and the +C<@ARGV> array at file scopes or within the lexical scopes established by the C, C, C, and C constructs. -See also unshift(), push(), and pop(). Shift() and unshift() do the -same thing to the left end of an array that pop() and push() do to the +See also C, C, and C. C and C do the +same thing to the left end of an array that C and C do to the right end. =item shmctl ID,CMD,ARG -Calls the System V IPC function shmctl. If CMD is &IPC_STAT, then ARG -must be a variable which will hold the returned shmid_ds structure. -Returns like ioctl: the undefined value for error, "0 but true" for -zero, or the actual return value otherwise. +Calls the System V IPC function shmctl. You'll probably have to say + + use IPC::SysV; + +first to get the correct constant definitions. If CMD is C, +then ARG must be a variable which will hold the returned C +structure. Returns like ioctl: the undefined value for error, "C<0> but +true" for zero, or the actual return value otherwise. +See also C documentation. =item shmget KEY,SIZE,FLAGS Calls the System V IPC function shmget. Returns the shared memory segment id, or the undefined value if there is an error. +See also C documentation. =item shmread ID,VAR,POS,SIZE @@ -2909,24 +3182,35 @@ segment id, or the undefined value if there is an error. Reads or writes the System V shared memory segment ID starting at position POS for size SIZE by attaching to it, copying in/out, and -detaching from it. When reading, VAR must be a variable which will +detaching from it. When reading, VAR must be a variable that will hold the data read. When writing, if STRING is too long, only SIZE bytes are used; if STRING is too short, nulls are written to fill out SIZE bytes. Return TRUE if successful, or FALSE if there is an error. +See also C documentation. =item shutdown SOCKET,HOW Shuts down a socket connection in the manner indicated by HOW, which has the same interpretation as in the system call of the same name. + shutdown(SOCKET, 0); # I/we have stopped reading data + shutdown(SOCKET, 1); # I/we have stopped writing data + shutdown(SOCKET, 2); # I/we have stopped using this socket + +This is useful with sockets when you want to tell the other +side you're done writing but not done reading, or vice versa. +It's also a more insistent form of close because it also +disables the filedescriptor in any forked copies in other +processes. + =item sin EXPR =item sin Returns the sine of EXPR (expressed in radians). If EXPR is omitted, -returns sine of $_. +returns sine of C<$_>. -For the inverse sine operation, you may use the POSIX::asin() +For the inverse sine operation, you may use the C function, or use this relation: sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) } @@ -2936,25 +3220,28 @@ function, or use this relation: =item sleep Causes the script to sleep for EXPR seconds, or forever if no EXPR. -May be interrupted by sending the process a SIGALRM. Returns the -number of seconds actually slept. You probably cannot mix alarm() and -sleep() calls, because sleep() is often implemented using alarm(). +May be interrupted if the process receives a signal such as C. +Returns the number of seconds actually slept. You probably cannot +mix C and C calls, because C is often implemented +using C. On some older systems, it may sleep up to a full second less than what you requested, depending on how it counts seconds. Most modern systems -always sleep the full amount. +always sleep the full amount. They may appear to sleep longer than that, +however, because your process might not be scheduled right away in a +busy multitasking system. For delays of finer granularity than one second, you may use Perl's -syscall() interface to access setitimer(2) if your system supports it, -or else see L below. +C interface to access setitimer(2) if your system supports it, +or else see L above. -See also the POSIX module's sigpause() function. +See also the POSIX module's C function. =item socket SOCKET,DOMAIN,TYPE,PROTOCOL Opens a socket of the specified kind and attaches it to filehandle SOCKET. DOMAIN, TYPE, and PROTOCOL are specified the same as for the -system call of the same name. You should "use Socket;" first to get +system call of the same name. You should "C" first to get the proper definitions imported. See the example in L. =item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL @@ -2964,6 +3251,16 @@ specified type. DOMAIN, TYPE, and PROTOCOL are specified the same as for the system call of the same name. If unimplemented, yields a fatal error. Returns TRUE if successful. +Some systems defined C in terms of C, in which a call +to C is essentially: + + use Socket; + socketpair(Rdr, Wtr, AF_UNIX, SOCK_STREAM, PF_UNSPEC); + shutdown(Rdr, 1); # no more writing for reader + shutdown(Wtr, 0); # no more reading for writer + +See L for an example of socketpair use. + =item sort SUBNAME LIST =item sort BLOCK LIST @@ -2971,24 +3268,25 @@ error. Returns TRUE if successful. =item sort LIST Sorts the LIST and returns the sorted list value. If SUBNAME or BLOCK -is omitted, sorts in standard string comparison order. If SUBNAME is +is omitted, Cs in standard string comparison order. If SUBNAME is specified, it gives the name of a subroutine that returns an integer -less than, equal to, or greater than 0, depending on how the elements +less than, equal to, or greater than C<0>, depending on how the elements of the array are to be ordered. (The C=E> and C operators are extremely useful in such routines.) SUBNAME may be a -scalar variable name, in which case the value provides the name of the -subroutine to use. In place of a SUBNAME, you can provide a BLOCK as -an anonymous, in-line sort subroutine. +scalar variable name (unsubscripted), in which case the value provides +the name of (or a reference to) the actual subroutine to use. In place +of a SUBNAME, you can provide a BLOCK as an anonymous, in-line sort +subroutine. In the interests of efficiency the normal calling code for subroutines is bypassed, with the following effects: the subroutine may not be a recursive subroutine, and the two elements to be compared are passed into -the subroutine not via @_ but as the package global variables $a and -$b (see example below). They are passed by reference, so don't -modify $a and $b. And don't try to declare them as lexicals either. +the subroutine not via C<@_> but as the package global variables C<$a> and +C<$b> (see example below). They are passed by reference, so don't +modify C<$a> and C<$b>. And don't try to declare them as lexicals either. You also cannot exit out of the sort block or subroutine using any of the -loop control operators described in L or with goto(). +loop control operators described in L or with C. When C is in effect, C sorts LIST according to the current collation locale. See L. @@ -3066,8 +3364,8 @@ Examples: $a->[2] cmp $b->[2] } map { [$_, /=(\d+)/, uc($_)] } @old; -If you're using strict, you I declare $a -and $b as lexicals. They are package globals. That means +If you're using strict, you I declare C<$a> +and C<$b> as lexicals. They are package globals. That means if you're in the C
package, it's @articles = sort {$main::b <=> $main::a} @files; @@ -3081,11 +3379,9 @@ but if you're in the C package, it's @articles = sort {$FooPack::b <=> $FooPack::a} @files; The comparison function is required to behave. If it returns -inconsistent results (sometimes saying $x[1] is less than $x[2] and -sometimes saying the opposite, for example) the Perl interpreter will -probably crash and dump core. This is entirely due to and dependent -upon your system's qsort(3) library routine; this routine often avoids -sanity checks in the interest of speed. +inconsistent results (sometimes saying C<$x[1]> is less than C<$x[2]> and +sometimes saying the opposite, for example) the results are not +well-defined. =item splice ARRAY,OFFSET,LENGTH,LIST @@ -3094,22 +3390,26 @@ sanity checks in the interest of speed. =item splice ARRAY,OFFSET Removes the elements designated by OFFSET and LENGTH from an array, and -replaces them with the elements of LIST, if any. Returns the elements -removed from the array. The array grows or shrinks as necessary. If -LENGTH is omitted, removes everything from OFFSET onward. The -following equivalences hold (assuming C<$[ == 0>): - - push(@a,$x,$y) splice(@a,$#a+1,0,$x,$y) +replaces them with the elements of LIST, if any. In list context, +returns the elements removed from the array. In scalar context, +returns the last element removed, or C if no elements are +removed. The array grows or shrinks as necessary. +If OFFSET is negative then it start that far from the end of the array. +If LENGTH is omitted, removes everything from OFFSET onward. +If LENGTH is negative, leave that many elements off the end of the array. +The following equivalences hold (assuming C<$[ == 0>): + + push(@a,$x,$y) splice(@a,@a,0,$x,$y) pop(@a) splice(@a,-1) shift(@a) splice(@a,0,1) unshift(@a,$x,$y) splice(@a,0,0,$x,$y) - $a[$x] = $y splice(@a,$x,1,$y); + $a[$x] = $y splice(@a,$x,1,$y) Example, assuming array lengths are passed before arrays: sub aeq { # compare two list values - local(@a) = splice(@_,0,shift); - local(@b) = splice(@_,0,shift); + my(@a) = splice(@_,0,shift); + my(@b) = splice(@_,0,shift); return 0 unless @a == @b; # same len? while (@a) { return 0 if pop(@a) ne pop(@b); @@ -3126,22 +3426,24 @@ Example, assuming array lengths are passed before arrays: =item split -Splits a string into an array of strings, and returns it. +Splits a string into an array of strings, and returns it. By default, +empty leading fields are preserved, and empty trailing ones are deleted. -If not in a list context, returns the number of fields found and splits into -the @_ array. (In a list context, you can force the split into @_ by -using C as the pattern delimiters, but it still returns the array -value.) The use of implicit split to @_ is deprecated, however. +If not in list context, returns the number of fields found and splits into +the C<@_> array. (In list context, you can force the split into C<@_> by +using C as the pattern delimiters, but it still returns the list +value.) The use of implicit split to C<@_> is deprecated, however, because +it clobbers your subroutine arguments. -If EXPR is omitted, splits the $_ string. If PATTERN is also omitted, +If EXPR is omitted, splits the C<$_> string. If PATTERN is also omitted, splits on whitespace (after skipping any leading whitespace). Anything matching PATTERN is taken to be a delimiter separating the fields. (Note that the delimiter may be longer than one character.) -If LIMIT is specified and is not negative, splits into no more than -that many fields (though it may split into fewer). If LIMIT is -unspecified, trailing null fields are stripped (which potential users -of pop() would do well to remember). If LIMIT is negative, it is +If LIMIT is specified and positive, splits into no more than that +many fields (though it may split into fewer). If LIMIT is unspecified +or zero, trailing null fields are stripped (which potential users +of C would do well to remember). If LIMIT is negative, it is treated as if an arbitrarily large LIMIT had been specified. A pattern matching the null string (not to be confused with @@ -3172,7 +3474,7 @@ produces the list value (1, '-', 10, ',', 20) -If you had the entire header of a normal Unix email message in $header, +If you had the entire header of a normal Unix email message in C<$header>, you could split it up into fields and their values this way: $header =~ s/\n\s+/ /g; # fix continuation lines @@ -3183,38 +3485,38 @@ patterns that vary at runtime. (To do runtime compilation only once, use C.) As a special case, specifying a PATTERN of space (C<' '>) will split on -white space just as split with no arguments does. Thus, split(' ') can +white space just as C with no arguments does. Thus, C can be used to emulate B's default behavior, whereas C will give you as many null initial fields as there are leading spaces. -A split on /\s+/ is like a split(' ') except that any leading -whitespace produces a null first field. A split with no arguments +A C on C is like a C except that any leading +whitespace produces a null first field. A C with no arguments really does a C internally. Example: - open(passwd, '/etc/passwd'); - while () { - ($login, $passwd, $uid, $gid, $gcos, - $home, $shell) = split(/:/); - ... + open(PASSWD, '/etc/passwd'); + while () { + ($login, $passwd, $uid, $gid, + $gcos, $home, $shell) = split(/:/); + #... } -(Note that $shell above will still have a newline on it. See L, +(Note that C<$shell> above will still have a newline on it. See L, L, and L.) =item sprintf FORMAT, LIST -Returns a string formatted by the usual printf conventions of the -C library function sprintf(). See L or L +Returns a string formatted by the usual C conventions of the +C library function C. See L or L on your system for an explanation of the general principles. -Perl does all of its own sprintf() formatting -- it emulates the C -function sprintf(), but it doesn't use it (except for floating-point +Perl does its own C formatting -- it emulates the C +function C, but it doesn't use it (except for floating-point numbers, and even then only the standard modifiers are allowed). As a -result, any non-standard extensions in your local sprintf() are not +result, any non-standard extensions in your local C are not available from Perl. -Perl's sprintf() permits the following universally-known conversions: +Perl's C permits the following universally-known conversions: %% a percent sign %c a character with the given number @@ -3252,10 +3554,11 @@ and the conversion letter: + prefix positive number with a plus sign - left-justify within the field 0 use zeros, not spaces, to right-justify - # prefix octal with "0", hex with "0x" + # prefix non-zero octal with "0", non-zero hex with "0x" number minimum field width - .number "precision": digits after decimal point for floating-point, - max length for string, minimum length for integer + .number "precision": digits after decimal point for + floating-point, max length for string, minimum length + for integer l interpret integer as C type "long" or "unsigned long" h interpret integer as C type "short" or "unsigned short" @@ -3263,11 +3566,11 @@ There is also one Perl-specific flag: V interpret integer as Perl's standard integer type -Where a number would appear in the flags, an asterisk ("*") may be +Where a number would appear in the flags, an asterisk ("C<*>") may be used instead, in which case Perl uses the next item in the parameter list as the given number (that is, as the field width or precision). -If a field width obtained through "*" is negative, it has the same -effect as the '-' flag: left-justification. +If a field width obtained through "C<*>" is negative, it has the same +effect as the "C<->" flag: left-justification. If C is in effect, the character used for the decimal point in formatted real numbers is affected by the LC_NUMERIC locale. @@ -3278,24 +3581,24 @@ See L. =item sqrt Return the square root of EXPR. If EXPR is omitted, returns square -root of $_. +root of C<$_>. =item srand EXPR =item srand -Sets the random number seed for the C operator. If EXPR is +Sets the random number seed for the C operator. If EXPR is omitted, uses a semi-random value based on the current time and process ID, among other things. In versions of Perl prior to 5.004 the default -seed was just the current time(). This isn't a particularly good seed, +seed was just the current C. This isn't a particularly good seed, so many old programs supply their own seed value (often C