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
+A 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
=item Functions for SCALARs or strings
C<chomp>, C<chop>, C<chr>, C<crypt>, C<hex>, C<index>, C<lc>, C<lcfirst>,
-C<length>, C<oct>, C<ord>, C<pack>, C<q/STRING/>, C<qq/STRING/>, C<qu/STRING/>,
-C<reverse>, C<rindex>, C<sprintf>, C<substr>, C<tr///>, C<uc>, C<ucfirst>,
-C<y///>
+C<length>, C<oct>, C<ord>, C<pack>, C<q/STRING/>, C<qq/STRING/>, C<reverse>,
+C<rindex>, C<sprintf>, C<substr>, C<tr///>, C<uc>, C<ucfirst>, C<y///>
=item Regular expressions and pattern matching
C<accept>, C<bind>, C<connect>, C<getpeername>, C<getsockname>,
C<getsockopt>, C<listen>, C<recv>, C<send>, C<setsockopt>, C<shutdown>,
-C<socket>, C<socketpair>
+C<sockatmark>, C<socket>, C<socketpair>
=item System V interprocess communication functions
=item Functions new in perl5
C<abs>, C<bless>, C<chomp>, C<chr>, C<exists>, C<formline>, C<glob>,
-C<import>, C<lc>, C<lcfirst>, C<map>, C<my>, C<no>, C<our>, C<prototype>,
+C<import>, C<lc>, C<lcfirst>, C<map>, C<my>, C<no>, C<our>, C<prototype>,
C<qx>, C<qw>, C<readline>, C<readpipe>, C<ref>, C<sub*>, C<sysopen>, C<tie>,
C<tied>, C<uc>, C<ucfirst>, C<untie>, C<use>
C<semget>, C<semop>, C<setgrent>, C<sethostent>, C<setnetent>,
C<setpgrp>, C<setpriority>, C<setprotoent>, C<setpwent>,
C<setservent>, C<setsockopt>, C<shmctl>, C<shmget>, C<shmread>,
-C<shmwrite>, C<socket>, C<socketpair>, C<stat>, C<symlink>, C<syscall>,
-C<sysopen>, C<system>, C<times>, C<truncate>, C<umask>, C<unlink>,
+C<shmwrite>, C<sockatmark>, C<socket>, C<socketpair>,
+C<stat>, C<symlink>, C<syscall>, C<sysopen>, C<system>,
+C<times>, C<truncate>, C<umask>, C<unlink>,
C<utime>, C<wait>, C<waitpid>
For more information about the portability of these functions, see
-g File has setgid bit set.
-k File has sticky bit set.
- -T File is an ASCII text file.
+ -T File is an ASCII text file (heuristic guess).
-B File is a "binary" file (opposite of -T).
- -M Age of file in days when script started.
+ -M Script start time minus file modification time, in days.
-A Same for access time.
- -C Same for inode change time.
+ -C Same for inode change time (Unix, may differ for other platforms)
Example:
while (<>) {
- chop;
+ chomp;
next unless -f $_; # ignore specials
#...
}
characters with the high bit set. If too many strange characters (>30%)
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
+or C<-B> is used on a filehandle, the current IO buffer is examined
rather than the first block. Both C<-T> and C<-B> return true on a null
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>
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
that lstat() and C<-l> will leave values in the stat structure for the
-symbolic link, not the real file.) Example:
+symbolic link, not the real file.) (Also, if the stat buffer was filled by
+a C<lstat> call, C<-T> and C<-B> will reset it with the results of C<stat _>).
+Example:
print "Can do.\n" if -r $a || -w _ || -x _;
=item alarm
Arranges to have a SIGALRM delivered to this process after the
-specified number of seconds have elapsed. If SECONDS is not specified,
-the value stored in C<$_> 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 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.
+specified number of wallclock seconds have elapsed. If SECONDS is not
+specified, the value stored in C<$_> is used. (On some machines,
+unfortunately, the elapsed time may be up to one second less or more
+than you specified because of how seconds are counted, and process
+scheduling may delay the delivery of the signal even further.)
+
+Only one timer may be counting at once. Each call disables the
+previous timer, and an 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
four-argument version of select() leaving the first three arguments
undefined, or you might be able to use the C<syscall> interface to
-access setitimer(2) if your system supports it. The Time::HiRes module
-from CPAN may also prove useful.
+access setitimer(2) if your system supports it. The Time::HiRes
+module (from CPAN, and starting from Perl 5.8 part of the standard
+distribution) may also prove useful.
It is usually a mistake to intermix C<alarm> and C<sleep> calls.
(C<sleep> may be internally implemented in your system with C<alarm>)
Arranges for FILEHANDLE to be read or written in "binary" or "text" mode
on systems where the run-time libraries distinguish between binary and
text files. If FILEHANDLE is an expression, the value is taken as the
-name of the filehandle. DISCIPLINE can be either of C<":raw"> for
-binary mode or C<":crlf"> for "text" mode. If the DISCIPLINE is
-omitted, it defaults to C<":raw">.
+name of the filehandle. DISCIPLINE can be either of C<:raw> for
+binary mode or C<:crlf> for "text" mode. If the DISCIPLINE is
+omitted, it defaults to C<:raw>. Returns true on success, C<undef> on
+failure. The C<:raw> are C<:clrf>, and any other directives of the
+form C<:...>, are called I/O I<disciplines>.
+
+The C<open> pragma can be used to establish default I/O disciplines.
+See L<open>.
-binmode() should be called after open() but before any I/O is done on
-the filehandle.
+In general, binmode() should be called after open() but before any I/O
+is done on the filehandle. Calling binmode() will flush any possibly
+pending buffered input or output data on the handle. The only
+exception to this is the C<:encoding> discipline that changes
+the default character encoding of the handle, see L<open>.
+The C<:encoding> discipline sometimes needs to be called in
+mid-stream, and it doesn't flush the stream.
-On many systems binmode() currently has no effect, but in future, it
-will be extended to support user-defined input and output disciplines.
On some systems binmode() is necessary when you're not working with a
text file. For the sake of portability it is a good idea to always use
it when appropriate, and to never use it when it isn't appropriate.
In other words: Regardless of platform, use binmode() on binary
files, and do not use binmode() on text files.
-The C<open> pragma can be used to establish default disciplines.
-See L<open>.
-
The operating system, device drivers, C libraries, and Perl run-time
system all work together to let the programmer treat a single
character (C<\n>) as the line terminator, irrespective of the external
platforms the external representation of C<\n> is made up of more than
one character.
-Mac OS and all variants of Unix use a single character to end each line
-in the external representation of text (even though that single
-character is not necessarily the same across these platforms).
-Consequently binmode() has no effect on these operating systems. In
-other systems like VMS, MS-DOS and the various flavors of MS-Windows
-your program sees a C<\n> as a simple C<\cJ>, but what's stored in text
-files are the two characters C<\cM\cJ>. That means that, if you don't
-use binmode() on these systems, C<\cM\cJ> sequences on disk will be
-converted to C<\n> on input, and any C<\n> in your program will be
-converted back to C<\cM\cJ> on output. This is what you want for text
-files, but it can be disastrous for binary files.
+Mac OS, all variants of Unix, and Stream_LF files on VMS use a single
+character to end each line in the external representation of text (even
+though that single character is CARRIAGE RETURN on Mac OS and LINE FEED
+on Unix and most VMS files). Consequently binmode() has no effect on
+these operating systems. In other systems like OS/2, DOS and the various
+flavors of MS-Windows your program sees a C<\n> as a simple C<\cJ>, but
+what's stored in text files are the two characters C<\cM\cJ>. That means
+that, if you don't use binmode() on these systems, C<\cM\cJ> sequences on
+disk will be converted to C<\n> on input, and any C<\n> in your program
+will be converted back to C<\cM\cJ> on output. This is what you want for
+text files, but it can be disastrous for binary files.
Another consequence of using binmode() (on some systems) is that
special end-of-file markers will be seen as part of the data stream.
Be aware that the optimizer might have optimized call frames away before
C<caller> had a chance to get the information. That means that C<caller(N)>
might not return information about the call frame you expect it do, for
-C<< N > 1 >>. In particular, C<@DB::args> might have information from the
+C<< N > 1 >>. In particular, C<@DB::args> might have information from the
previous time C<caller> was called.
=item chdir EXPR
-Changes the working directory to EXPR, if possible. If EXPR is omitted,
+Changes the working directory to EXPR, if possible. If EXPR is omitted,
changes to the directory specified by C<$ENV{HOME}>, if set; if not,
-changes to the directory specified by C<$ENV{LOGDIR}>. If neither is
-set, C<chdir> does nothing. It returns true upon success, false
-otherwise. See the example under C<die>.
+changes to the directory specified by C<$ENV{LOGDIR}>. (Under VMS, the
+variable C<$ENV{SYS$LOGIN}> is also checked, and used if it is set.) If
+neither is set, C<chdir> does nothing. It returns true upon success,
+false otherwise. See the example under C<die>.
=item chmod LIST
=item chomp VARIABLE
-=item chomp LIST
+=item chomp( LIST )
=item chomp
mode (C<$/ = "">), it removes all trailing newlines from the string.
When in slurp mode (C<$/ = undef>) or fixed-length record mode (C<$/> is
a reference to an integer or the like, see L<perlvar>) chomp() won't
-remove anything.
+remove anything.
If VARIABLE is omitted, it chomps C<$_>. Example:
while (<>) {
=item chop VARIABLE
-=item chop LIST
+=item chop( LIST )
=item chop
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<s/\n//> because it neither
+chopped. It is much more efficient than C<s/.$//s> because it neither
scans nor copies the string. If VARIABLE is omitted, chops C<$_>.
-Example:
-
- while (<>) {
- chop; # avoid \n on last field
- @array = split(/:/);
- #...
- }
-
If VARIABLE is a hash, it chops the hash's values, but not its keys.
-You can actually chop anything that's an lvalue, including an assignment:
-
- chop($cwd = `pwd`);
- chop($answer = <STDIN>);
+You can actually chop anything that's an lvalue, including an assignment.
If you chop a list, each element is chopped. Only the value of the
last C<chop> is returned.
Returns the character represented by that NUMBER in the character set.
For example, C<chr(65)> is C<"A"> in either ASCII or Unicode, and
-chr(0x263a) is a Unicode smiley face. Within the scope of C<use utf8>,
-characters higher than 127 are encoded in Unicode; if you don't want
-this, temporarily C<use bytes> or use C<pack("C*",...)>
+chr(0x263a) is a Unicode smiley face. Note that characters from 127
+to 255 (inclusive) are by default not encoded in Unicode for backward
+compatibility reasons (but see L<encoding>).
-For the reverse, use L</ord>.
-See L<utf8> for more about Unicode.
+For the reverse, use L</ord>.
+See L<perlunicode> and L<encoding> for more about Unicode.
If NUMBER is omitted, uses C<$_>.
=item close
-Closes the file or pipe associated with the file handle, returning true
-only if stdio successfully flushes buffers and closes the system file
-descriptor. Closes the currently selected filehandle if the argument
-is omitted.
+Closes the file or pipe associated with the file handle, returning
+true only if IO buffers are successfully flushed and closes the system
+file descriptor. Closes the currently selected filehandle if the
+argument is omitted.
You don't have to close FILEHANDLE if you are immediately going to do
another C<open> on it, because C<open> will close it for you. (See
If the file handle came from a piped open C<close> will additionally
return false if one of the other system calls involved fails or if the
program exits with non-zero status. (If the only problem was that the
-program exited non-zero C<$!> will be set to C<0>.) Closing a pipe
+program exited non-zero C<$!> will be set to C<0>.) Closing a pipe
also waits for the process executing on the pipe to complete, in case you
-want to look at the output of the pipe afterwards, and
+want to look at the output of the pipe afterwards, and
implicitly puts the exit status value of that command into C<$?>.
Prematurely closing the read end of a pipe (i.e. before the process
the password file for lousy passwords, amongst other things. Only the
guys wearing white hats should do this.
-Note that C<crypt> 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
+Note that C<crypt> is intended to be a one-way function, much like
+breaking eggs to make an omelette. There is no (known) corresponding
+decrypt function (in other words, the crypt() is a one-way hash
+function). As a result, this function isn't all that useful for
cryptography. (For that, see your nearby CPAN mirror.)
-When verifying an existing encrypted string you should use the encrypted
-text as the salt (like C<crypt($plain, $crypted) eq $crypted>). This
-allows your code to work with the standard C<crypt> and with more
-exotic implementations. When choosing a new salt create a random two
-character string whose characters come from the set C<[./0-9A-Za-z]>
-(like C<join '', ('.', '/', 0..9, 'A'..'Z', 'a'..'z')[rand 64, rand 64]>).
+When verifying an existing encrypted string you should use the
+encrypted text as the salt (like C<crypt($plain, $crypted) eq
+$crypted>). This allows your code to work with the standard C<crypt>
+and with more exotic implementations. In other words, do not assume
+anything about the returned string itself, or how many bytes in
+the encrypted string matter.
+
+Traditionally the result is a string of 13 bytes: two first bytes of
+the salt, followed by 11 bytes from the set C<[./0-9A-Za-z]>, and only
+the first eight bytes of the encrypted string mattered, but
+alternative hashing schemes (like MD5), higher level security schemes
+(like C2), and implementations on non-UNIX platforms may produce
+different strings.
+
+When choosing a new salt create a random two character string whose
+characters come from the set C<[./0-9A-Za-z]> (like C<join '', ('.',
+'/', 0..9, 'A'..'Z', 'a'..'z')[rand 64, rand 64]>).
Here's an example that makes sure that whoever runs this program knows
their own password:
on your favorite CPAN mirror for a slew of potentially useful
modules.
+If using crypt() on a Unicode string (which I<potentially> has
+characters with codepoints above 255), Perl tries to make sense
+of the situation by trying to downgrade (a copy of the string)
+the string back to an eight-bit byte string before calling crypt()
+(on that copy). If that works, good. If not, crypt() dies with
+C<Wide character in crypt>.
+
=item dbmclose HASH
[This function has been largely superseded by the C<untie> function.]
Given an expression that specifies a hash element, array element, hash slice,
or array slice, deletes the specified element(s) from the hash or array.
In the case of an array, if the array elements happen to be at the end,
-the size of the array will shrink to the highest element that tests
+the size of the array will shrink to the highest element that tests
true for exists() (or 0 if no such element exists).
Returns each element so deleted or the undefined value if there was no such
eval { ... };
die unless $@ =~ /Expected exception/;
+If LIST is empty and C<$@> contains an object reference that has a
+C<PROPAGATE> method, that method will be called with additional file
+and line number parameters. The return value replaces the value in
+C<$@>. ie. as if C<<$@ = eval { $@->PROPAGATE(__FILE__, __LINE__) };>>
+were called.
+
If C<$@> is empty then the string C<"Died"> is used.
die() can also be called with a reference argument. If this happens to be
as the first line of the handler (see L<perlvar/$^S>). Because
this promotes strange action at a distance, this counterintuitive
-behavior may be fixed in a future release.
+behavior may be fixed in a future release.
=item do BLOCK
is just like
- scalar eval `cat stat.pl`;
+ eval `cat stat.pl`;
except that it's more efficient and concise, keeps track of the current
filename for error messages, searches the @INC libraries, and updates
You might like to use C<do> to read in a program configuration
file. Manual error checking can be done this way:
- # read in config files: system first, then user
+ # read in config files: system first, then user
for $file ("/share/prog/defaults.rc",
- "$ENV{HOME}/.someprogrc")
+ "$ENV{HOME}/.someprogrc")
{
unless ($return = do $file) {
warn "couldn't parse $file: $@" if $@;
B<WARNING>: Any files opened at the time of the dump will I<not>
be open any more when the program is reincarnated, with possible
-resulting confusion on the part of Perl.
+resulting confusion on the part of Perl.
This function is now largely obsolete, partly because it's very
hard to convert a core file into an executable, and because the
real compiler backends for generating portable bytecode and compilable
-C code have superseded it.
+C code have superseded it. That's why you should now invoke it as
+C<CORE::dump()>, if you don't want to be warned against a possible
+typo.
If you're looking to use L<dump> to speed up your program, consider
generating bytecode or native C code as described in L<perlcc>. If
you're just trying to accelerate a CGI script, consider using the
-C<mod_perl> extension to B<Apache>, or the CPAN module, Fast::CGI.
+C<mod_perl> extension to B<Apache>, or the CPAN module, CGI::Fast.
You might also consider autoloading or selfloading, which at least
-make your program I<appear> to run faster.
+make your program I<appear> to run faster.
=item each HASH
C<< <> >> operator. Since C<< <> >> isn't explicitly opened,
as a normal filehandle is, an C<eof()> before C<< <> >> has been
used will cause C<@ARGV> to be examined to determine if input is
-available.
+available. Similarly, an C<eof()> after C<< <> >> has returned
+end-of-file will assume you are processing another C<@ARGV> list,
+and if you haven't set C<@ARGV>, will read input from C<STDIN>;
+see L<perlop/"I/O Operators">.
In a C<< while (<>) >> loop, C<eof> or C<eof(ARGV)> can be used to
detect the end of each file, C<eof()> will only detect the end of the
# reset line numbering on each input file
while (<>) {
- next if /^\s*#/; # skip comments
+ next if /^\s*#/; # skip comments
print "$.\t$_";
} continue {
close ARGV if eof; # Not eof()!
error message. If there was no error, C<$@> is guaranteed to be a null
string. Beware that using C<eval> neither silences perl from printing
warnings to STDERR, nor does it stuff the text of warning messages into C<$@>.
-To do either of those, you have to use the C<$SIG{__WARN__}> facility. See
-L</warn> and L<perlvar>.
+To do either of those, you have to use the C<$SIG{__WARN__}> facility, or
+turn off warnings inside the BLOCK or EXPR using S<C<no warnings 'all'>>.
+See L</warn>, L<perlvar>, L<warnings> and L<perllexwarn>.
Note that, because C<eval> traps otherwise-fatal errors, it is useful for
determining whether a particular feature (such as C<socket> or C<symlink>)
the entire argument is passed to the system's command shell for parsing
(this is C</bin/sh -c> on Unix platforms, but varies on other platforms).
If there are no shell metacharacters in the argument, it is split into
-words and passed directly to C<execvp>, which is more efficient.
+words and passed directly to C<execvp>, which is more efficient.
Examples:
exec '/bin/echo', 'Your arguments are: ', @ARGV;
=item exp
-Returns I<e> (the natural logarithm base) to the power of EXPR.
+Returns I<e> (the natural logarithm base) to the power of EXPR.
If EXPR is omitted, gives C<exp($_)>.
=item fcntl FILEHANDLE,FUNCTION,SCALAR
use Fcntl;
first to get the correct constant definitions. Argument processing and
-value return works just like C<ioctl> below.
+value return works just like C<ioctl> below.
For example:
use Fcntl;
If FILEHANDLE is an expression, the value is taken as an indirect
filehandle, generally its name.
-You can use this to find out whether two handles refer to the
+You can use this to find out whether two handles refer to the
same underlying descriptor:
if (fileno(THIS) == fileno(THAT)) {
print "THIS and THAT are dups\n";
- }
+ }
+
+(Filehandles connected to memory objects via new features of C<open> may
+return undefined even though they are open.)
+
=item flock FILEHANDLE,OPERATION
implement lockf(3) in terms of fcntl(2) locking, though, so the
differing semantics shouldn't bite too many people.
+Note that the fcntl(2) emulation of flock(3) requires that FILEHANDLE
+be open with read intent to use LOCK_SH and requires that it be open
+with write intent to use LOCK_EX.
+
Note also that some versions of C<flock> cannot lock things over the
network; you would need to use the more system-specific C<fcntl> for
that. If you like you can force Perl to ignore your system's flock(2)
use User::pwent;
$is_his = (stat($filename)->uid == pwent($whoever)->uid);
-Even though it looks like they're the same method calls (uid),
-they aren't, because a C<File::stat> object is different from
+Even though it looks like they're the same method calls (uid),
+they aren't, because a C<File::stat> object is different from
a C<User::pwent> object.
=item getsockname SOCKET
use Socket;
$mysockaddr = getsockname(SOCK);
($port, $myaddr) = sockaddr_in($mysockaddr);
- printf "Connect to %s [%s]\n",
+ printf "Connect to %s [%s]\n",
scalar gethostbyaddr($myaddr, AF_INET),
inet_ntoa($myaddr);
=item gmtime EXPR
-Converts a time as returned by the time function to a 8-element list
+Converts a time as returned by the time function to an 8-element list
with the time localized for the standard Greenwich time zone.
Typically used as follows:
- # 0 1 2 3 4 5 6 7
+ # 0 1 2 3 4 5 6 7
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday) =
gmtime(time);
indicating December. $year is the number of years since 1900. That
is, $year is C<123> in year 2023. $wday is the day of the week, with
0 indicating Sunday and 3 indicating Wednesday. $yday is the day of
-the year, in the range C<0..364> (or C<0..365> in leap years.)
+the year, in the range C<0..364> (or C<0..365> in leap years.)
Note that the $year element is I<not> simply the last two digits of
the year. If you assume it is, then you create non-Y2K-compliant
including out of subroutines, but it's usually better to use some other
construct such as C<last> or C<die>. The author of Perl has never felt the
need to use this form of C<goto> (in Perl, that is--C is another matter).
+(The difference being that C does not offer named loops combined with
+loop control. Perl does, and this replaces most structured uses of C<goto>
+in other languages.)
The C<goto-EXPR> form expects a label name, whose scope will be resolved
dynamically. This allows for computed C<goto>s per FORTRAN, but isn't
goto ("FOO", "BAR", "GLARCH")[$i];
-The C<goto-&NAME> form is quite different from the other forms of C<goto>.
-In fact, it isn't a goto in the normal sense at all, and doesn't have
-the stigma associated with other gotos. Instead, it
-substitutes a call to the named subroutine for the currently running
-subroutine. This is used by C<AUTOLOAD> subroutines that wish to load
-another subroutine and then pretend that the other subroutine had been
-called in the first place (except that any modifications to C<@_>
+The C<goto-&NAME> form is quite different from the other forms of
+C<goto>. In fact, it isn't a goto in the normal sense at all, and
+doesn't have the stigma associated with other gotos. Instead, it
+exits the current subroutine (losing any changes set by local()) and
+immediately calls in its place the named subroutine using the current
+value of @_. This is used by C<AUTOLOAD> subroutines that wish to
+load another subroutine and then pretend that the other subroutine had
+been called in the first place (except that any modifications to C<@_>
in the current subroutine are propagated to the other subroutine.)
After the C<goto>, not even C<caller> will be able to tell that this
routine was called first.
print hex 'aF'; # same
Hex strings may only represent integers. Strings that would cause
-integer overflow trigger a warning.
+integer overflow trigger a warning. Leading whitespace is not stripped,
+unlike oct().
=item import
There is no builtin C<import> function. It is just an ordinary
method (subroutine) defined (or inherited) by modules that wish to export
names to another module. The C<use> function calls the C<import> method
-for the package used. See also L</use()>, L<perlmod>, and L<Exporter>.
+for the package used. See also L</use>, L<perlmod>, and L<Exporter>.
=item index STR,SUBSTR,POSITION
passed rather than a pointer to the string value. To guarantee this to be
true, add a C<0> to the scalar before using it.) The C<pack> and C<unpack>
functions may be needed to manipulate the values of structures used by
-C<ioctl>.
+C<ioctl>.
The return value of C<ioctl> (and C<fcntl>) is as follows:
@keys = keys %ENV;
@values = values %ENV;
- while (@keys) {
+ while (@keys) {
print pop(@keys), '=', pop(@values), "\n";
}
=item lc
-Returns an lowercased version of EXPR. This is the internal function
-implementing the C<\L> escape in double-quoted strings.
-Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>
-and L<utf8>.
+Returns a lowercased version of EXPR. This is the internal function
+implementing the C<\L> escape in double-quoted strings. Respects
+current LC_CTYPE locale if C<use locale> in force. See L<perllocale>
+and L<perlunicode> for more details about locale and Unicode support.
If EXPR is omitted, uses C<$_>.
=item lcfirst
-Returns the value of EXPR with the first character lowercased. This is
-the internal function implementing the C<\l> escape in double-quoted strings.
-Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>.
+Returns the value of EXPR with the first character lowercased. This
+is the internal function implementing the C<\l> escape in
+double-quoted strings. Respects current LC_CTYPE locale if C<use
+locale> in force. See L<perllocale> and L<perlunicode> for more
+details about locale and Unicode support.
If EXPR is omitted, uses C<$_>.
=item length
Returns the length in characters of the value of EXPR. If EXPR is
-omitted, returns length of C<$_>. Note that this cannot be used on
+omitted, returns length of C<$_>. Note that this cannot be used on
an entire array or hash to find out how many elements these have.
For that, use C<scalar @array> and C<scalar keys %hash> respectively.
=item link OLDFILE,NEWFILE
Creates a new filename linked to the old filename. Returns true for
-success, false otherwise.
+success, false otherwise.
=item listen SOCKET,QUEUESIZE
Does the same thing that the listen system call does. Returns true if
-it succeeded, false otherwise. See the example in L<perlipc/"Sockets: Client/Server Communication">.
+it succeeded, false otherwise. See the example in
+L<perlipc/"Sockets: Client/Server Communication">.
=item local EXPR
You really probably want to be using C<my> instead, because C<local> isn't
-what most people think of as "local". See
+what most people think of as "local". See
L<perlsub/"Private Variables via my()"> for details.
A local modifies the listed variables to be local to the enclosing
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 lock
-
- lock I<THING>
+=item lock THING
This function places an advisory lock on a variable, subroutine,
or referenced object contained in I<THING> until the lock goes out
of scope. This is a built-in function only if your version of Perl
-was built with threading enabled, and if you've said C<use Threads>.
-Otherwise a user-defined function by this name will be called. See
-L<Thread>.
+was built with threading enabled, and if you've said C<use Thread>.
+Otherwise a user-defined function by this name will be called.
+See L<Thread>.
=item log EXPR
sub log10 {
my $n = shift;
return log($n)/log(10);
- }
+ }
See also L</exp> for the inverse operation.
%hash = map { ("\L$_", 1) } @array # this also works
%hash = map { lc($_), 1 } @array # as does this.
%hash = map +( lc($_), 1 ), @array # this is EXPR and works!
-
+
%hash = map ( lc($_), 1 ), @array # evaluates to (1, @array)
or to force an anon hash constructor use C<+{>
Interprets EXPR as an octal string and returns the corresponding
value. (If EXPR happens to start off with C<0x>, interprets it as a
hex string. If EXPR starts off with C<0b>, it is interpreted as a
-binary string.) The following will handle decimal, binary, octal, and
-hex in the standard Perl or C notation:
+binary string. Leading whitespace is ignored in all three cases.)
+The following will handle decimal, binary, octal, and hex in the standard
+Perl or C notation:
$val = oct($val) if $val =~ /^0/;
automatically convert strings into numbers as needed, this automatic
conversion assumes base 10.)
-=item open FILEHANDLE,MODE,LIST
-
=item open FILEHANDLE,EXPR
+=item open FILEHANDLE,MODE,EXPR
+
+=item open FILEHANDLE,MODE,EXPR,LIST
+
+=item open FILEHANDLE,MODE,REFERENCE
+
=item open FILEHANDLE
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. (This is considered a symbolic
-reference, so C<use strict 'refs'> should I<not> be in effect.)
-
-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<my>--will not work
-for this purpose; so if you're using C<my>, specify EXPR in your call
-to open.) See L<perlopentut> for a kinder, gentler explanation of opening
-files.
-
-If MODE is C<< '<' >> or nothing, the file is opened for input.
-If MODE is C<< '>' >>, the file is truncated and opened for
-output, being created if necessary. If MODE is C<<< '>>' >>>,
-the file is opened for appending, again being created if necessary.
-You can put a C<'+'> in front of the C<< '>' >> or C<< '<' >> to indicate that
-you want both read and write access to the file; thus C<< '+<' >> is almost
-always preferred for read/write updates--the C<< '+>' >> 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<perlrun> for a better approach. The file is created with
-permissions of C<0666> modified by the process' C<umask> value.
-
-These various prefixes correspond to the fopen(3) modes of C<'r'>, C<'r+'>,
-C<'w'>, C<'w+'>, C<'a'>, and C<'a+'>.
+FILEHANDLE.
+
+(The following is a comprehensive reference to open(): for a gentler
+introduction you may consider L<perlopentut>.)
+
+If FILEHANDLE is an undefined lexical (C<my>) variable the variable is
+assigned a reference to a new anonymous filehandle, otherwise if
+FILEHANDLE is an expression, its value is used as the name of the real
+filehandle wanted. (This is considered a symbolic reference, so C<use
+strict 'refs'> should I<not> be in effect.)
+
+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<my>--will not work for this purpose; so if you're
+using C<my>, specify EXPR in your call to open.)
+
+If three or more arguments are specified then the mode of opening and
+the file name are separate. If MODE is C<< '<' >> or nothing, the file
+is opened for input. If MODE is C<< '>' >>, the file is truncated and
+opened for output, being created if necessary. If MODE is C<<< '>>' >>>,
+the file is opened for appending, again being created if necessary.
+
+You can put a C<'+'> in front of the C<< '>' >> or C<< '<' >> to
+indicate that you want both read and write access to the file; thus
+C<< '+<' >> is almost always preferred for read/write updates--the C<<
+'+>' >> 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<perlrun> for a
+better approach. The file is created with permissions of C<0666>
+modified by the process' C<umask> value.
+
+These various prefixes correspond to the fopen(3) modes of C<'r'>,
+C<'r+'>, C<'w'>, C<'w+'>, C<'a'>, and C<'a+'>.
In the 2-arguments (and 1-argument) form of the call the mode and
filename should be concatenated (in this order), possibly separated by
-spaces. It is possible to omit the mode if the mode is C<< '<' >>.
+spaces. It is possible to omit the mode in these forms if the mode is
+C<< '<' >>.
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
and L<perlipc/"Bidirectional Communication with Another Process">
for alternatives.)
-If MODE is C<'|-'>, the filename is interpreted as a
-command to which output is to be piped, and if MODE is
-C<'-|'>, the filename is interpreted as a command which pipes output to
-us. In the 2-arguments (and 1-argument) form one should replace dash
-(C<'-'>) with the command. See L<perlipc/"Using open() for IPC">
-for more examples of this. (You are not allowed to C<open> to a command
-that pipes both in I<and> out, but see L<IPC::Open2>, L<IPC::Open3>,
-and L<perlipc/"Bidirectional Communication"> for alternatives.)
+For three or more arguments if MODE is C<'|-'>, the filename is
+interpreted as a command to which output is to be piped, and if MODE
+is C<'-|'>, the filename is interpreted as a command which pipes
+output to us. In the 2-arguments (and 1-argument) form one should
+replace dash (C<'-'>) with the command.
+See L<perlipc/"Using open() for IPC"> for more examples of this.
+(You are not allowed to C<open> to a command that pipes both in I<and>
+out, but see L<IPC::Open2>, L<IPC::Open3>, and
+L<perlipc/"Bidirectional Communication"> for alternatives.)
+
+In the three-or-more argument form of pipe opens, if LIST is specified
+(extra arguments after the command name) then LIST becomes arguments
+to the command invoked if the platform supports it. The meaning of
+C<open> with more than three arguments for non-pipe modes is not yet
+specified. Experimental "layers" may give extra LIST arguments
+meaning.
In the 2-arguments (and 1-argument) form opening C<'-'> opens STDIN
-and opening C<< '>-' >> opens STDOUT.
+and opening C<< '>-' >> opens STDOUT.
-Open returns
-nonzero upon success, the undefined value otherwise. If the C<open>
-involved a pipe, the return value happens to be the pid of the
-subprocess.
+You may use the three-argument form of open to specify
+I<I/O disciplines> that affect how the input and output
+are processed: see L</binmode> and L<open>. For example
-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</binmode> for tips for
-dealing with this. The key distinction between systems that need C<binmode>
-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<binmode>. The rest need it.
+ open(FH, "<:utf8", "file")
+
+will open the UTF-8 encoded file containing Unicode characters,
+see L<perluniintro>.
+
+Open returns nonzero upon success, the undefined value otherwise. If
+the C<open> involved a pipe, the return value happens to be the pid of
+the subprocess.
+
+If you're running Perl on a system that distinguishes between text
+files and binary files, then you should check out L</binmode> for tips
+for dealing with this. The key distinction between systems that need
+C<binmode> 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<binmode>. The rest need it.
+
+In the three argument form MODE may also contain a list of IO "layers"
+(see L<open> and L<PerlIO> for more details) to be applied to the
+handle. This can be used to achieve the effect of C<binmode> as well
+as more complex behaviours.
When opening a file, it's usually a bad idea to continue normal execution
if the request failed, so C<open> is frequently used in connection with
the return value from opening a file. The infrequent exception is when
working with an unopened filehandle is actually what you want to do.
+As a special case the 3 arg form with a read/write mode and the third
+argument being C<undef>:
+
+ open(TMP, "+>", undef) or die ...
+
+opens a filehandle to an anonymous temporary file.
+
+File handles can be opened to "in memory" files held in Perl scalars via:
+
+ open($fh,'>', \$variable) || ..
+
Examples:
$ARTICLE = 100;
open(EXTRACT, "|sort >/tmp/Tmp$$") # $$ is our process id
or die "Can't start sort: $!";
+ # in memory files
+ open(MEMORY,'>', \$var)
+ or die "Can't open memory file: $!";
+ print MEMORY "foo!\n"; # output will end up in $var
+
# process argument list of files along with any includes
foreach $file (@ARGV) {
C<< < >>, C<< +> >>, C<<< +>> >>>, and C<< +< >>. 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.) Duping file handles is not yet supported for 3-argument
-open().
+IO buffers.) If you use the 3 arg form then you can pass either a number,
+the name of a filehandle or the normal "reference to a glob".
Here is a script that saves, redirects, and restores STDOUT and
STDERR:
#!/usr/bin/perl
- open(OLDOUT, ">&STDOUT");
+ open(my $oldout, ">&", \*STDOUT);
open(OLDERR, ">&STDERR");
open(STDOUT, '>', "foo.out") || die "Can't redirect stdout";
print STDOUT "stdout 2\n";
print STDERR "stderr 2\n";
-If you specify C<< '<&=N' >>, where C<N> is a number, then Perl will do an
-equivalent of C's C<fdopen> of that file descriptor; this is more
-parsimonious of file descriptors. For example:
+If you specify C<< '<&=N' >>, where C<N> is a number, then Perl will
+do an equivalent of C's C<fdopen> of that file descriptor; this is
+more parsimonious of file descriptors. For example:
open(FILEHANDLE, "<&=$fd")
-Note that this feature depends on the fdopen() C library function.
-On many UNIX systems, fdopen() is known to fail when file descriptors
+or
+
+ open(FILEHANDLE, "<&=", $fd)
+
+Note that if Perl is using the standard C libraries' fdopen() then on
+many UNIX systems, fdopen() is known to fail when file descriptors
exceed a certain value, typically 255. If you need more file
-descriptors than that, consider rebuilding Perl to use the C<sfio>
-library.
+descriptors than that, consider rebuilding Perl to use the C<PerlIO>.
+
+You can see whether Perl has been compiled with PerlIO or not by
+running C<perl -V> and looking for C<useperlio=> line. If C<useperlio>
+is C<define>, you have PerlIO, otherwise you don't.
If you open a pipe on the command C<'-'>, i.e., either C<'|-'> or C<'-|'>
with 2-arguments (or 1-argument) form of open(), then
open(FOO, "|tr '[a-z]' '[A-Z]'");
open(FOO, '|-', "tr '[a-z]' '[A-Z]'");
open(FOO, '|-') || exec 'tr', '[a-z]', '[A-Z]';
+ open(FOO, '|-', "tr", '[a-z]', '[A-Z]');
open(FOO, "cat -n '$file'|");
open(FOO, '-|', "cat -n '$file'");
open(FOO, '-|') || exec 'cat', '-n', $file;
+ open(FOO, '-|', "cat", '-n', $file);
+
+The last example in each block shows the pipe as "list form", which is
+not yet supported on all platforms.
See L<perlipc/"Safe Pipe Opens"> for more examples of this.
to set C<$|> ($AUTOFLUSH in English) or call the C<autoflush()> method
of C<IO::Handle> on any open handles.
-On systems that support a
-close-on-exec flag on files, the flag will be set for the newly opened
-file descriptor as determined by the value of $^F. See L<perlvar/$^F>.
+On systems that support a close-on-exec flag on files, the flag will
+be set for the newly opened file descriptor as determined by the value
+of $^F. See L<perlvar/$^F>.
Closing any piped filehandle causes the parent process to wait for the
child to finish, and returns the status value in C<$?>.
-The filename passed to 2-argument (or 1-argument) form of open()
-will have leading and trailing
-whitespace deleted, and the normal redirection characters
-honored. This property, known as "magic open",
+The filename passed to 2-argument (or 1-argument) form of open() will
+have leading and trailing whitespace deleted, and the normal
+redirection characters honored. This property, known as "magic open",
can often be used to good effect. A user could specify a filename of
F<"rsh cat file |">, or you could change certain filenames as needed:
=item ord
-Returns the numeric (ASCII or Unicode) value of the first character of EXPR. If
-EXPR is omitted, uses C<$_>. For the reverse, see L</chr>.
-See L<utf8> for more about Unicode.
+Returns the numeric (the native 8-bit encoding, like ASCII or EBCDIC,
+or Unicode) value of the first character of EXPR. If EXPR is omitted,
+uses C<$_>.
+
+For the reverse, see L</chr>.
+See L<perlunicode> and L<encoding> for more about Unicode.
=item our EXPR
+=item our EXPR : ATTRIBUTES
+
An C<our> declares the listed variables to be valid globals within
the enclosing block, file, or C<eval>. That is, it has the same
scoping rules as a "my" declaration, but does not create a local
our $bar; # emits warning
+An C<our> declaration may also have a list of attributes associated
+with it. B<WARNING>: This is an experimental feature that may be
+changed or removed in future releases of Perl. It should not be
+relied upon.
+
+The only currently recognized attribute is C<unique> which indicates
+that a single copy of the global is to be used by all interpreters
+should the program happen to be running in a multi-interpreter
+environment. (The default behaviour would be for each interpreter to
+have its own copy of the global.) In such an environment, this
+attribute also has the effect of making the global readonly.
+Examples:
+
+ our @EXPORT : unique = qw(foo);
+ our %EXPORT_TAGS : unique = (bar => [qw(aa bb cc)]);
+ our $VERSION : unique = "1.00";
+
+Multi-interpreter environments can come to being either through the
+fork() emulation on Windows platforms, or by embedding perl in a
+multi-threaded application. The C<unique> attribute does nothing in
+all other environments.
+
=item pack TEMPLATE,LIST
Takes a LIST of values and converts it into a string using the rules
like its machine-level representation. For example, on 32-bit machines
a converted integer may be represented by a sequence of 4 bytes.
-The TEMPLATE is a
-sequence of characters that give the order and type of values, as
-follows:
+The TEMPLATE is a sequence of characters that give the order and type
+of values, as follows:
a A string with arbitrary binary data, will be null padded.
- A An ASCII string, will be space padded.
- Z A null terminated (asciz) string, will be null padded.
+ A A text (ASCII) string, will be space padded.
+ Z A null terminated (ASCIZ) string, will be null padded.
b A bit string (ascending bit order inside each byte, like vec()).
B A bit string (descending bit order inside each byte).
integer values _and_ if Perl has been compiled to support those.
Causes a fatal error otherwise.)
+ j A signed integer value (a Perl internal integer, IV).
+ J An unsigned integer value (a Perl internal unsigned integer, UV).
+
f A single-precision float in the native format.
d A double-precision float in the native format.
+ F A floating point value in the native native format
+ (a Perl internal floating point value, NV).
+ D A long double-precision float in the native format.
+ (Long doubles are available only if your system supports long
+ double values _and_ if Perl has been compiled to support those.
+ Causes a fatal error otherwise.)
+
p A pointer to a null-terminated string.
P A pointer to a structure (fixed-length string).
u A uuencoded string.
- U A Unicode character number. Encodes to UTF-8 internally.
- Works even if C<use utf8> is not in effect.
+ U A Unicode character number. Encodes to UTF-8 internally
+ (or UTF-EBCDIC in EBCDIC platforms).
w A BER compressed integer. Its bytes represent an unsigned
integer in base 128, most significant digit first, with as
x A null byte.
X Back up a byte.
@ Null fill to absolute position.
+ ( Start of a ()-group.
The following rules apply:
Each letter may optionally be followed by a number giving a repeat
count. With all types except C<a>, C<A>, C<Z>, 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, except for C<@>, C<x>, C<X>, where it is equivalent
-to C<0>, and C<u>, where it is equivalent to 1 (or 45, what is the
-same).
+C<H>, C<@>, C<x>, C<X> 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, except for C<@>, C<x>, C<X>, where it is
+equivalent to C<0>, and C<u>, where it is equivalent to 1 (or 45, what
+is the same). A numeric repeat count may optionally be enclosed in
+brackets, as in C<pack 'C[80]', @arr>.
+
+One can replace the numeric repeat count by a template enclosed in brackets;
+then the packed length of this template in bytes is used as a count.
+For example, C<x[L]> skips a long (it skips the number of bytes in a long);
+the template C<$t X[$t] $t> unpack()s twice what $t unpacks.
+If the template in brackets contains alignment commands (such as C<x![d]>),
+its packed length is calculated as if the start of the template has the maximal
+possible alignment.
When used with C<Z>, C<*> results in the addition of a trailing null
byte (so the packed result will be one longer than the byte C<length>
the packed structure contains a byte count followed by the string itself.
You write I<length-item>C</>I<string-item>.
-The I<length-item> can be any C<pack> template letter,
-and describes how the length value is packed.
-The ones likely to be of most use are integer-packing ones like
-C<n> (for Java strings), C<w> (for ASN.1 or SNMP)
-and C<N> (for Sun XDR).
+The I<length-item> can be any C<pack> template letter, and describes
+how the length value is packed. The ones likely to be of most use are
+integer-packing ones like C<n> (for Java strings), C<w> (for ASN.1 or
+SNMP) and C<N> (for Sun XDR).
The I<string-item> must, at present, be C<"A*">, C<"a*"> or C<"Z*">.
For C<unpack> the length of the string is obtained from the I<length-item>,
print $Config{longlongsize}, "\n";
(The C<$Config{longlongsize}> will be undefine if your system does
-not support long longs.)
+not support long longs.)
=item *
-The integer formats C<s>, C<S>, C<i>, C<I>, C<l>, and C<L>
+The integer formats C<s>, C<S>, C<i>, C<I>, C<l>, C<L>, C<j>, and C<J>
are inherently non-portable between processors and operating systems
because they obey the native byteorder and endianness. For example a
-4-byte integer 0x12345678 (305419896 decimal) be ordered natively
+4-byte integer 0x12345678 (305419896 decimal) would be ordered natively
(arranged in and handled by the CPU registers) into bytes as
0x12 0x34 0x56 0x78 # big-endian
Basically, the Intel and VAX CPUs are little-endian, while everybody
else, for example Motorola m68k/88k, PPC, Sparc, HP PA, Power, and
Cray are big-endian. Alpha and MIPS can be either: Digital/Compaq
-used/uses them in little-endian mode; SGI/Cray uses them in big-endian mode.
+used/uses them in little-endian mode; SGI/Cray uses them in big-endian
+mode.
The names `big-endian' and `little-endian' are comic references to
the classic "Gulliver's Travels" (via the paper "On Holy Wars and a
and C<'87654321'> are big-endian.
If you want portable packed integers use the formats C<n>, C<N>,
-C<v>, and C<V>, their byte endianness and size is known.
+C<v>, and C<V>, their byte endianness and size are known.
See also L<perlport>.
=item *
=item *
+A ()-group is a sub-TEMPLATE enclosed in parentheses. A group may
+take a repeat count, both as postfix, and via the C</> template
+character.
+
+=item *
+
+C<x> and C<X> accept C<!> modifier. In this case they act as
+alignment commands: they jump forward/back to the closest position
+aligned at a multiple of C<count> bytes. For example, to pack() or
+unpack() C's C<struct {char c; double d; char cc[2]}> one may need to
+use the template C<C x![d] d C[2]>; this assumes that doubles must be
+aligned on the double's size.
+
+For alignment commands C<count> of 0 is equivalent to C<count> of 1;
+both result in no-ops.
+
+=item *
+
A comment in a TEMPLATE starts with C<#> and goes to the end of line.
=item *
=item package NAMESPACE
-=item package
+=item package
Declares the compilation unit as being in the given namespace. The scope
of the package declaration is from the declaration itself through the end
still seen in older code).
If NAMESPACE is omitted, then there is no current package, and all
-identifiers must be fully qualified or lexicals. This is stricter
-than C<use strict>, since it also extends to function names.
+identifiers must be fully qualified or lexicals. However, you are
+strongly advised not to make use of this feature. Its use can cause
+unexpected behaviour, even crashing some versions of Perl. It is
+deprecated, and will be removed from a future release.
See L<perlmod/"Packages"> for more information about packages, modules,
and classes. See L<perlsub> for other scoping issues.
Opens a pair of connected pipes like the corresponding system call.
Note that if you set up a loop of piped processes, deadlock can occur
unless you are very careful. In addition, note that Perl's pipes use
-stdio buffering, so you may need to set C<$|> to flush your WRITEHANDLE
+IO buffering, so you may need to set C<$|> to flush your WRITEHANDLE
after each command, depending on the application.
See L<IPC::Open2>, L<IPC::Open3>, and L<perlipc/"Bidirectional Communication">
Equivalent to C<print FILEHANDLE sprintf(FORMAT, LIST)>, except that C<$\>
(the output record separator) is not appended. The first argument
-of the list will be interpreted as the C<printf> format. If C<use locale> is
-in effect, the character used for the decimal point in formatted real numbers
-is affected by the LC_NUMERIC locale. See L<perllocale>.
+of the list will be interpreted as the C<printf> format. See C<sprintf>
+for an explanation of the format argument. If C<use locale> is in effect,
+the character used for the decimal point in formatted real numbers is
+affected by the LC_NUMERIC locale. See L<perllocale>.
Don't fall into the trap of using a C<printf> when a simple
C<print> would do. The C<print> is more efficient and less
=item qr/STRING/
-=item qu/STRING/
+=item qx/STRING/
=item qw/STRING/
-=item qx/STRING/
-
Generalized quotes. See L<perlop/"Regexp Quote-Like Operators">.
=item quotemeta EXPR
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 C<1> is used. Automatically calls C<srand> unless
-C<srand> has already been called. See also C<srand>.
+omitted, or a C<0>, the value C<1> is used. Automatically calls C<srand>
+unless C<srand> has already been called. See also C<srand>.
+
+Apply C<int()> to the value returned by C<rand()> if you want random
+integers instead of random fractional numbers. For example,
+
+ int(rand(10))
+
+returns a random integer between C<0> and C<9>, inclusive.
(Note: If your rand function consistently returns numbers that are too
large or too small, then your version of Perl was probably compiled
=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, C<0>
-at end of file, or undef if there was an error. SCALAR will be grown
-or shrunk to the length actually read. If SCALAR needs growing, the
-new bytes will be zero bytes. An OFFSET may be specified to place
-the read data into some other place in SCALAR than the beginning.
-The call is actually implemented in terms of stdio's fread(3) call.
-To get a true read(2) system call, see C<sysread>.
+Attempts to read LENGTH I<characters> of data into variable SCALAR
+from the specified FILEHANDLE. Returns the number of characters
+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. If SCALAR
+needs growing, the new bytes will be zero bytes. An OFFSET may be
+specified to place the read data into some other place in SCALAR than
+the beginning. The call is actually implemented in terms of either
+Perl's or system's fread() call. To get a true read(2) system call,
+see C<sysread>.
+
+Note the I<characters>: depending on the status of the filehandle,
+either (8-bit) bytes or characters are read. By default all
+filehandles operate on bytes, but for example if the filehandle has
+been opened with the C<:utf8> discipline (see L</open>, and the C<open>
+pragma, L<open>), the I/O will operate on characters, not bytes.
=item readdir DIRHANDLE
=item recv SOCKET,SCALAR,LENGTH,FLAGS
-Receives a message on a socket. Attempts to receive LENGTH bytes of
-data into variable SCALAR from the specified SOCKET filehandle. SCALAR
-will be grown or shrunk to the length actually read. Takes the same
-flags as the system call of the same name. Returns the address of the
-sender if SOCKET's protocol supports this; returns an empty string
-otherwise. If there's an error, returns the undefined value. This call
-is actually implemented in terms of recvfrom(2) system call. See
-L<perlipc/"UDP: Message Passing"> for examples.
+Receives a message on a socket. Attempts to receive LENGTH characters
+of data into variable SCALAR from the specified SOCKET filehandle.
+SCALAR will be grown or shrunk to the length actually read. Takes the
+same flags as the system call of the same name. Returns the address
+of the sender if SOCKET's protocol supports this; returns an empty
+string otherwise. If there's an error, returns the undefined value.
+This call is actually implemented in terms of recvfrom(2) system call.
+See L<perlipc/"UDP: Message Passing"> for examples.
+
+Note the I<characters>: depending on the status of the socket, either
+(8-bit) bytes or characters are received. By default all sockets
+operate on bytes, but for example if the socket has been changed using
+binmode() to operate with the C<:utf8> discipline (see the C<open>
+pragma, L<open>), the I/O will operate on characters, not bytes.
=item redo LABEL
}
if (UNIVERSAL::isa($r, "HASH")) { # for subclassing
print "r is a reference to something that isa hash.\n";
- }
+ }
See also L<perlref>.
=item require
-Demands some semantics specified by EXPR, or by C<$_> if EXPR is not
-supplied.
+Demands a version of Perl specified by VERSION, or demands some semantics
+specified by EXPR or by C<$_> if EXPR is not supplied.
+
+VERSION may be either a numeric argument such as 5.006, which will be
+compared to C<$]>, or a literal of the form v5.6.1, which will be compared
+to C<$^V> (aka $PERL_VERSION). A fatal error is produced at run time if
+VERSION is greater than the version of the current Perl interpreter.
+Compare with L</use>, which can do a similar check at compile time.
-If a VERSION is specified as a literal of the form v5.6.1,
-demands that the current version of Perl (C<$^V> or $PERL_VERSION) be
-at least as recent as that version, at run time. (For compatibility
-with older versions of Perl, a numeric argument will also be interpreted
-as VERSION.) Compare with L</use>, which can do a similar check at
-compile time.
+Specifying VERSION as a literal of the form v5.6.1 should generally be
+avoided, because it leads to misleading error messages under earlier
+versions of Perl which do not support this syntax. The equivalent numeric
+version should be used instead.
require v5.6.1; # run time version check
require 5.6.1; # ditto
- require 5.005_03; # float version allowed for compatibility
+ require 5.006_001; # ditto; preferred for backwards compatibility
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
In other words, if you try this:
- require Foo::Bar; # a splendid bareword
+ require Foo::Bar; # a splendid bareword
-The require function will actually look for the "F<Foo/Bar.pm>" file in the
+The require function will actually look for the "F<Foo/Bar.pm>" file in the
directories specified in the C<@INC> array.
But if you try this:
#or
require "Foo::Bar"; # not a bareword because of the ""
-The require function will look for the "F<Foo::Bar>" file in the @INC array and
+The require function will look for the "F<Foo::Bar>" file in the @INC array and
will complain about not finding "F<Foo::Bar>" there. In this case you can do:
eval "require $class";
+You can also insert hooks into the import facility, by putting directly
+Perl code into the @INC array. There are three forms of hooks: subroutine
+references, array references and blessed objects.
+
+Subroutine references are the simplest case. When the inclusion system
+walks through @INC and encounters a subroutine, this subroutine gets
+called with two parameters, the first being a reference to itself, and the
+second the name of the file to be included (e.g. "F<Foo/Bar.pm>"). The
+subroutine should return C<undef> or a filehandle, from which the file to
+include will be read. If C<undef> is returned, C<require> will look at
+the remaining elements of @INC.
+
+If the hook is an array reference, its first element must be a subroutine
+reference. This subroutine is called as above, but the first parameter is
+the array reference. This enables to pass indirectly some arguments to
+the subroutine.
+
+In other words, you can write:
+
+ push @INC, \&my_sub;
+ sub my_sub {
+ my ($coderef, $filename) = @_; # $coderef is \&my_sub
+ ...
+ }
+
+or:
+
+ push @INC, [ \&my_sub, $x, $y, ... ];
+ sub my_sub {
+ my ($arrayref, $filename) = @_;
+ # Retrieve $x, $y, ...
+ my @parameters = @$arrayref[1..$#$arrayref];
+ ...
+ }
+
+If the hook is an object, it must provide an INC method, that will be
+called as above, the first parameter being the object itself. (Note that
+you must fully qualify the sub's name, as it is always forced into package
+C<main>.) Here is a typical code layout:
+
+ # In Foo.pm
+ package Foo;
+ sub new { ... }
+ sub Foo::INC {
+ my ($self, $filename) = @_;
+ ...
+ }
+
+ # In the main program
+ push @INC, new Foo(...);
+
+Note that these hooks are also permitted to set the %INC entry
+corresponding to the files they have loaded. See L<perlvar/%INC>.
+
For a yet-more-powerful import facility, see L</use> and L<perlmod>.
=item reset EXPR
=item return
-Returns from a subroutine, C<eval>, or C<do FILE> with the value
+Returns from a subroutine, C<eval>, or C<do FILE> 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 C<wantarray>). If no EXPR
is given, returns an empty list in list context, the undefined value in
scalar context, and (of course) nothing at all in a void context.
-(Note that in the absence of a explicit C<return>, a subroutine, eval,
+(Note that in the absence of an explicit C<return>, a subroutine, eval,
or do FILE will automatically return the value of the last expression
evaluated.)
Sets FILEHANDLE's position, just like the C<fseek> call of C<stdio>.
FILEHANDLE may be an expression whose value gives the name of the
-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 C<SEEK_SET>, C<SEEK_CUR>, and C<SEEK_END>
-(start of the file, current position, end of the file) from the Fcntl
-module. Returns C<1> upon success, C<0> otherwise.
+filehandle. The values for WHENCE are C<0> to set the new position
+I<in bytes> 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 C<SEEK_SET>,
+C<SEEK_CUR>, and C<SEEK_END> (start of the file, current position, end
+of the file) from the Fcntl module. Returns C<1> upon success, C<0>
+otherwise.
+
+Note the I<in bytes>: even if the filehandle has been set to
+operate on characters (for example by using the C<:utf8> open
+discipline), tell() will return byte offsets, not character offsets
+(because implementing that would render seek() and tell() rather slow).
If you want to position file for C<sysread> or C<syswrite>, don't use
C<seek>--buffering makes its effect on the file's system position
but it I<does> clear the end-of-file condition on the handle, so that the
next C<< <FILE> >> makes Perl try again to read something. We hope.
-If that doesn't work (some stdios are particularly cantankerous), then
-you may need something more like this:
+If that doesn't work (some IO implementations are particularly
+cantankerous), then you may need something more like this:
for (;;) {
for ($curpos = tell(FILE); $_ = <FILE>;
Any of the bit masks can also be undef. The timeout, if specified, is
in seconds, which may be fractional. Note: not all implementations are
-capable of returning the$timeleft. If not, they always return
+capable of returning the $timeleft. If not, they always return
$timeleft equal to the supplied $timeout.
You can effect a sleep of 250 milliseconds this way:
=item semop KEY,OPSTRING
Calls the System V IPC function semop to perform semaphore operations
-such as signaling and waiting. OPSTRING must be a packed array of
+such as signalling and waiting. OPSTRING must be a packed array of
semop structures. Each semop structure can be generated with
-C<pack("sss", $semnum, $semop, $semflag)>. The number of semaphore
+C<pack("s!3", $semnum, $semop, $semflag)>. 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:
- $semop = pack("sss", $semnum, -1, 0);
+ $semop = pack("s!3", $semnum, -1, 0);
die "Semaphore trouble: $!\n" unless semop($semid, $semop);
To signal the semaphore, replace C<-1> with C<1>. See also
=item send SOCKET,MSG,FLAGS
-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 C<sendto>. Returns
-the number of characters sent, or the undefined value if there is an
-error. The C system call sendmsg(2) is currently unimplemented.
-See L<perlipc/"UDP: Message Passing"> for examples.
+Sends a message on a socket. Attempts to send the scalar MSG to the
+SOCKET filehandle. 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 C<sendto>. Returns the number of
+characters sent, or the undefined value if there is an error. The C
+system call sendmsg(2) is currently unimplemented. See
+L<perlipc/"UDP: Message Passing"> for examples.
+
+Note the I<characters>: depending on the status of the socket, either
+(8-bit) bytes or characters are sent. By default all sockets operate
+on bytes, but for example if the socket has been changed using
+binmode() to operate with the C<:utf8> discipline (see L</open>, or
+the C<open> pragma, L<open>), the I/O will operate on characters, not
+bytes.
=item setpgrp PID,PGRP
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
+It's also a more insistent form of close because it also
disables the file descriptor in any forked copies in other
processes.
For delays of finer granularity than one second, you may use Perl's
C<syscall> interface to access setitimer(2) if your system supports
-it, or else see L</select> above. The Time::HiRes module from CPAN
-may also help.
+it, or else see L</select> above. The Time::HiRes module (from CPAN,
+and starting from Perl 5.8 part of the standard distribution) may also
+help.
See also the POSIX module's C<pause> function.
+=item sockatmark SOCKET
+
+Returns true if the socket is positioned at the out-of-band mark
+(also known as the urgent data mark), false otherwise. Use right
+after reading from the socket.
+
+Not available directly, one has to import the function from
+the IO::Socket extension
+
+ use IO::Socket 'sockatmark';
+
+Even this doesn't guarantee that sockatmark() really is available,
+though, because sockatmark() is a relatively recent addition to
+the family of socket functions. If it is unavailable, attempt to
+use it will fail
+
+ IO::Socket::atmark not implemented on this architecture ...
+
+See also L<IO::Socket>.
+
=item socket SOCKET,DOMAIN,TYPE,PROTOCOL
Opens a socket of the specified kind and attaches it to filehandle
shutdown(Rdr, 1); # no more writing for reader
shutdown(Wtr, 0); # no more reading for writer
-See L<perlipc> for an example of socketpair use.
+See L<perlipc> for an example of socketpair use. Perl 5.8 and later will
+emulate socketpair using IP sockets to localhost if your system implements
+sockets but not socketpair.
=item sort SUBNAME LIST
When C<use locale> is in effect, C<sort LIST> sorts LIST according to the
current collation locale. See L<perllocale>.
+Perl 5.6 and earlier used a quicksort algorithm to implement sort.
+That algorithm was not stable, and I<could> go quadratic. (A I<stable> sort
+preserves the input order of elements that compare equal. Although
+quicksort's run time is O(NlogN) when averaged over all arrays of
+length N, the time can be O(N**2), I<quadratic> behavior, for some
+inputs.) In 5.7, the quicksort implementation was replaced with
+a stable mergesort algorithm whose worst case behavior is O(NlogN).
+But benchmarks indicated that for some inputs, on some platforms,
+the original quicksort was faster. 5.8 has a sort pragma for
+limited control of the sort. Its rather blunt control of the
+underlying algorithm may not persist into future perls, but the
+ability to characterize the input or output in implementation
+independent ways quite probably will. See L</use>.
+
Examples:
# sort lexically
package main;
@new = sort other::backwards @old;
+ # guarantee stability, regardless of algorithm
+ use sort 'stable';
+ @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;
+
+ # force use of quicksort (not portable outside Perl 5.8)
+ use sort '_quicksort'; # note discouraging _
+ @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;
+
+ # similar to the previous example, but demand stability as well
+ use sort qw( _mergesort stable );
+ @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;
+
If you're using strict, you I<must not> declare $a
and $b as lexicals. They are package globals. That means
if you're in the C<main> package and type
If OFFSET is negative then it starts that far from the end of the array.
If LENGTH is omitted, removes everything from OFFSET onward.
If LENGTH is negative, leaves that many elements off the end of the array.
-If both OFFSET and LENGTH are omitted, removes everything.
+If both OFFSET and LENGTH are omitted, removes everything. If OFFSET is
+past the end of the array, perl issues a warning, and splices at the
+end of the array.
The following equivalences hold (assuming C<$[ == 0>):
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 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<pop> would do well to remember). If LIMIT is negative, it is
-treated as if an arbitrarily large LIMIT had been specified.
+If LIMIT is specified and positive, it represents the maximum number
+of fields the EXPR will be split into, though the actual number of
+fields returned depends on the number of times PATTERN matches within
+EXPR. If LIMIT is unspecified or zero, trailing null fields are
+stripped (which potential users of C<pop> would do well to remember).
+If LIMIT is negative, it is treated as if an arbitrarily large LIMIT
+had been specified. Note that splitting an EXPR that evaluates to the
+empty string always returns the empty list, regardless of the LIMIT
+specified.
A pattern matching the null string (not to be confused with
a null pattern C<//>, which is just one member of the set of patterns
produces the output 'h:i:t:h:e:r:e'.
-Empty leading (or trailing) fields are produced when there positive width
+Using the empty pattern C<//> specifically matches the null string, and is
+not be confused with the use of C<//> to mean "the last successful pattern
+match".
+
+Empty leading (or trailing) fields are produced when there are positive width
matches at the beginning (or end) of the string; a zero-width match at the
beginning (or end) of the string does not produce an empty field. For
example:
open(PASSWD, '/etc/passwd');
while (<PASSWD>) {
- ($login, $passwd, $uid, $gid,
+ chomp;
+ ($login, $passwd, $uid, $gid,
$gcos, $home, $shell) = split(/:/);
#...
}
-(Note that $shell above will still have a newline on it. See L</chop>,
-L</chomp>, and L</join>.)
+As with regular pattern matching, any capturing parentheses that are not
+matched in a C<split()> will be set to C<undef> when returned:
+
+ @fields = split /(A)|B/, "1A2B3";
+ # @fields is (1, 'A', 2, undef, 3)
=item sprintf FORMAT, LIST
%b an unsigned integer, in binary
%p a pointer (outputs the Perl value's address in hexadecimal)
%n special: *stores* the number of characters output so far
- into the next variable in the parameter list
+ into the next variable in the parameter list
Finally, for backward (and we do mean "backward") compatibility, Perl
permits these unnecessary but widely-supported conversions:
v interpret string as a vector of integers, output as
numbers separated either by dots, or by an arbitrary
string received from the argument list when the flag
- is preceded by C<*>
+ is preceded by "*"
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
=item srand
-Sets the random number seed for the C<rand> operator. If EXPR is
-omitted, uses a semi-random value supplied by the kernel (if it supports
-the F</dev/urandom> device) or 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 C<time>. This isn't a particularly good seed,
-so many old programs supply their own seed value (often C<time ^ $$> or
-C<time ^ ($$ + ($$ << 15))>), but that isn't necessary any more.
+Sets the random number seed for the C<rand> operator.
+
+The point of the function is to "seed" the C<rand> function so that
+C<rand> can produce a different sequence each time you run your
+program.
+
+If srand() is not called explicitly, it is called implicitly at the
+first use of the C<rand> operator. However, this was not the case in
+versions of Perl before 5.004, so if your script will run under older
+Perl versions, it should call C<srand>.
+
+Most programs won't even call srand() at all, except those that
+need a cryptographically-strong starting point rather than the
+generally acceptable default, which is based on time of day,
+process ID, and memory allocation, or the F</dev/urandom> device,
+if available.
+
+You can call srand($seed) with the same $seed to reproduce the
+I<same> sequence from rand(), but this is usually reserved for
+generating predictable results for testing or debugging.
+Otherwise, don't call srand() more than once in your program.
+
+Do B<not> call srand() (i.e. without an argument) more than once in
+a script. The internal state of the random number generator should
+contain more entropy than can be provided by any seed, so calling
+srand() again actually I<loses> randomness.
-In fact, it's usually not necessary to call C<srand> at all, because if
-it is not called explicitly, it is called implicitly at the first use of
-the C<rand> operator. However, this was not the case in version of Perl
-before 5.004, so if your script will run under older Perl versions, it
-should call C<srand>.
+Most implementations of C<srand> take an integer and will silently
+truncate decimal numbers. This means C<srand(42)> will usually
+produce the same results as C<srand(42.1)>. To be safe, always pass
+C<srand> an integer.
+
+In versions of Perl prior to 5.004 the default seed was just the
+current C<time>. This isn't a particularly good seed, so many old
+programs supply their own seed value (often C<time ^ $$> or C<time ^
+($$ + ($$ << 15))>), but that isn't necessary any more.
Note that you need something much more random than the default seed for
cryptographic purposes. Checksumming the compressed output of one or more
If you're particularly concerned with this, see the C<Math::TrulyRandom>
module in CPAN.
-Do I<not> call C<srand> multiple times in your program unless you know
-exactly what you're doing and why you're doing it. The point of the
-function is to "seed" the C<rand> function so that C<rand> can produce
-a different sequence each time you run your program. Just do it once at the
-top of your program, or you I<won't> get random numbers out of C<rand>!
-
Frequently called programs (like CGI scripts) that simply use
time ^ $$
under NFS.)
Because the mode contains both the file type and its permissions, you
-should mask off the file type portion and (s)printf using a C<"%o">
+should mask off the file type portion and (s)printf using a C<"%o">
if you want to see the real permissions.
$mode = (stat($filename))[2];
use File::stat;
$sb = stat($filename);
- printf "File is %s, size is %s, perm %04o, mtime %s\n",
+ printf "File is %s, size is %s, perm %04o, mtime %s\n",
$filename, $sb->size, $sb->mode & 07777,
scalar localtime $sb->mtime;
and the setuid/setgid/sticky bits
S_IFMT($mode) the part of $mode containing the file type
- which can be bit-anded with e.g. S_IFREG
+ which can be bit-anded with e.g. S_IFREG
or with the following functions
# The operators -f, -d, -l, -b, -c, -p, and -s.
There's a problem with C<syscall(&SYS_pipe)>: it returns the file
number of the read end of the pipe it creates. There is no way
-to retrieve the file number of the other end. You can avoid this
+to retrieve the file number of the other end. You can avoid this
problem by using C<pipe> instead.
=item sysopen FILEHANDLE,FILENAME,MODE
=item sysread FILEHANDLE,SCALAR,LENGTH
-Attempts to read LENGTH bytes of data into variable SCALAR from the
-specified FILEHANDLE, using the system call read(2). It bypasses stdio,
-so mixing this with other kinds of reads, C<print>, C<write>,
-C<seek>, C<tell>, or C<eof> can cause confusion because stdio
-usually buffers data. 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 so that the last byte actually read is the last byte of the
-scalar after the read.
+Attempts to read LENGTH I<characters> of data into variable SCALAR from
+the specified FILEHANDLE, using the system call read(2). It bypasses
+buffered IO, so mixing this with other kinds of reads, C<print>,
+C<write>, C<seek>, C<tell>, or C<eof> can cause confusion because
+stdio usually buffers data. Returns the number of characters actually
+read, C<0> at end of file, or undef if there was an error. SCALAR
+will be grown or shrunk so that the last byte actually read is the
+last byte of the scalar after the read.
+
+Note the I<characters>: depending on the status of the filehandle,
+either (8-bit) bytes or characters are read. By default all
+filehandles operate on bytes, but for example if the filehandle has
+been opened with the C<:utf8> discipline (see L</open>, and the C<open>
+pragma, L<open>), the I/O will operate on characters, not bytes.
An OFFSET may be specified to place the read data at some place in the
string other than the beginning. A negative OFFSET specifies
-placement at that many bytes counting backwards from the end of the
-string. A positive OFFSET greater than the length of SCALAR results
-in the string being padded to the required size with C<"\0"> bytes before
-the result of the read is appended.
+placement at that many characters counting backwards from the end of
+the string. A positive OFFSET greater than the length of SCALAR
+results in the string being padded to the required size with C<"\0">
+bytes before the result of the read is appended.
There is no syseof() function, which is ok, since eof() doesn't work
very well on device files (like ttys) anyway. Use sysread() and check
=item sysseek FILEHANDLE,POSITION,WHENCE
-Sets FILEHANDLE's system position using the system call lseek(2). It
-bypasses stdio, so mixing this with reads (other than C<sysread>),
-C<print>, C<write>, C<seek>, C<tell>, or C<eof> may cause confusion.
-FILEHANDLE may be an expression whose value gives the name of the
-filehandle. The values for WHENCE are C<0> to set the new position to
-POSITION, C<1> to set the it to the current position plus POSITION,
-and C<2> to set it to EOF plus POSITION (typically negative). For
-WHENCE, you may also use the constants C<SEEK_SET>, C<SEEK_CUR>, and
-C<SEEK_END> (start of the file, current position, end of the file)
-from the Fcntl module.
+Sets FILEHANDLE's system position I<in bytes> using the system call
+lseek(2). FILEHANDLE may be an expression whose value gives the name
+of the filehandle. The values for WHENCE are C<0> to set the new
+position to POSITION, C<1> to set the it to the current position plus
+POSITION, and C<2> to set it to EOF plus POSITION (typically
+negative).
+
+Note the I<in bytes>: even if the filehandle has been set to operate
+on characters (for example by using the C<:utf8> discipline), tell()
+will return byte offsets, not character offsets (because implementing
+that would render sysseek() very slow).
+
+sysseek() bypasses normal buffered io, so mixing this with reads (other
+than C<sysread>, for example >< or read()) C<print>, C<write>,
+C<seek>, C<tell>, or C<eof> may cause confusion.
+
+For WHENCE, you may also use the constants C<SEEK_SET>, C<SEEK_CUR>,
+and C<SEEK_END> (start of the file, current position, end of the file)
+from the Fcntl module. Use of the constants is also more portable
+than relying on 0, 1, and 2. For example to define a "systell" function:
+
+ use Fnctl 'SEEK_CUR';
+ sub systell { sysseek($_[0], 0, SEEK_CUR) }
Returns the new position, or the undefined value on failure. A position
of zero is returned as the string C<"0 but true">; thus C<sysseek> returns
to set C<$|> ($AUTOFLUSH in English) or call the C<autoflush()> method
of C<IO::Handle> on any open handles.
-The return value is the exit status of the program as
-returned by the C<wait> call. To get the actual exit value divide by
-256. See also L</exec>. This is I<not> what you want to use to capture
+The return value is the exit status of the program as returned by the
+C<wait> call. To get the actual exit value shift right by eight (see below).
+See also L</exec>. This is I<not> what you want to use to capture
the output from a command, for that you should use merely backticks or
C<qx//>, as described in L<perlop/"`STRING`">. Return value of -1
indicates a failure to start the program (inspect $! for the reason).
Like C<exec>, C<system> allows you to lie to a program about its name if
you use the C<system PROGRAM LIST> syntax. Again, see L</exec>.
-Because C<system> and backticks block C<SIGINT> and C<SIGQUIT>, killing the
-program they're running doesn't actually interrupt your program.
+Because C<system> and backticks block C<SIGINT> and C<SIGQUIT>,
+killing the program they're running doesn't actually interrupt
+your program.
@args = ("command", "arg1", "arg2");
system(@args) == 0
$signal_num = $? & 127;
$dumped_core = $? & 128;
+or more portably by using the W*() calls of the POSIX extension;
+see L<perlport> for more information.
+
When the arguments get executed via the system shell, results
and return codes will be subject to its quirks and capabilities.
See L<perlop/"`STRING`"> and L</exec> for details.
=item syswrite FILEHANDLE,SCALAR
-Attempts to write LENGTH bytes of data from variable SCALAR to the
-specified FILEHANDLE, using the system call write(2). If LENGTH
-is not specified, writes whole SCALAR. It bypasses stdio, so mixing
-this with reads (other than C<sysread())>, C<print>, C<write>,
-C<seek>, C<tell>, or C<eof> may cause confusion because stdio
-usually buffers data. Returns the number of bytes actually written,
-or C<undef> if there was an error. If the LENGTH is greater than
-the available data in the SCALAR after the OFFSET, only as much
-data as is available will be written.
+Attempts to write LENGTH characters of data from variable SCALAR to
+the specified FILEHANDLE, using the system call write(2). If LENGTH
+is not specified, writes whole SCALAR. It bypasses buffered IO, so
+mixing this with reads (other than C<sysread())>, C<print>, C<write>,
+C<seek>, C<tell>, or C<eof> may cause confusion because stdio usually
+buffers data. Returns the number of characters actually written, or
+C<undef> if there was an error. If the LENGTH is greater than the
+available data in the SCALAR after the OFFSET, only as much data as is
+available will be written.
An OFFSET may be specified to write the data from some part of the
string other than the beginning. A negative OFFSET specifies writing
-that many bytes counting backwards from the end of the string. In the
-case the SCALAR is empty you can use OFFSET but only zero offset.
+that many characters counting backwards from the end of the string.
+In the case the SCALAR is empty you can use OFFSET but only zero offset.
+
+Note the I<characters>: depending on the status of the filehandle,
+either (8-bit) bytes or characters are written. By default all
+filehandles operate on bytes, but for example if the filehandle has
+been opened with the C<:utf8> discipline (see L</open>, and the open
+pragma, L<open>), the I/O will operate on characters, not bytes.
=item tell FILEHANDLE
=item tell
-Returns the current position for FILEHANDLE, or -1 on error. FILEHANDLE
-may be an expression whose value gives the name of the actual filehandle.
-If FILEHANDLE is omitted, assumes the file last read.
+Returns the current position I<in bytes> for FILEHANDLE, or -1 on
+error. FILEHANDLE may be an expression whose value gives the name of
+the actual filehandle. If FILEHANDLE is omitted, assumes the file
+last read.
+
+Note the I<in bytes>: even if the filehandle has been set to
+operate on characters (for example by using the C<:utf8> open
+discipline), tell() will return byte offsets, not character offsets
+(because that would render seek() and tell() rather slow).
The return value of tell() for the standard streams like the STDIN
depends on the operating system: it may return -1 or something else.
There is no C<systell> function. Use C<sysseek(FH, 0, 1)> for that.
+Do not use tell() on a filehandle that has been opened using
+sysopen(), use sysseek() for that as described above. Why? Because
+sysopen() creates unbuffered, "raw", filehandles, while open() creates
+buffered filehandles. sysseek() make sense only on the first kind,
+tell() only makes sense on the second kind.
+
=item telldir DIRHANDLE
Returns the current position of the C<readdir> routines on DIRHANDLE.
($user,$system,$cuser,$csystem) = times;
+In scalar context, C<times> returns C<$user>.
+
=item tr///
The transliteration operator. Same as C<y///>. See L<perlop>.
=item uc
Returns an uppercased version of EXPR. This is the internal function
-implementing the C<\U> escape in double-quoted strings.
-Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>.
-Under Unicode (C<use utf8>) it uses the standard Unicode uppercase mappings. (It
-does not attempt to do titlecase mapping on initial letters. See C<ucfirst> for that.)
+implementing the C<\U> escape in double-quoted strings. Respects
+current LC_CTYPE locale if C<use locale> in force. See L<perllocale>
+and L<perlunicode> for more details about locale and Unicode support.
+It does not attempt to do titlecase mapping on initial letters. See
+C<ucfirst> for that.
If EXPR is omitted, uses C<$_>.
=item ucfirst
-Returns the value of EXPR with the first character
-in uppercase (titlecase in Unicode). This is
-the internal function implementing the C<\u> escape in double-quoted strings.
-Respects current LC_CTYPE locale if C<use locale> in force. See L<perllocale>
-and L<utf8>.
+Returns the value of EXPR with the first character in uppercase
+(titlecase in Unicode). This is the internal function implementing
+the C<\u> escape in double-quoted strings. Respects current LC_CTYPE
+locale if C<use locale> in force. See L<perllocale> and L<perlunicode>
+for more details about locale and Unicode support.
If EXPR is omitted, uses C<$_>.
If the repeat count of a field is larger than what the remainder of
the input string allows, repeat count is decreased. If the input string
-is longer than one described by the TEMPLATE, the rest is ignored.
+is longer than one described by the TEMPLATE, the rest is ignored.
See L</pack> for more examples and notes.
depending on how you look at it. Prepends list to the front of the
array, and returns the new number of elements in the array.
- unshift(ARGV, '-e') unless $ARGV[0] =~ /^-/;
+ unshift(@ARGV, '-e') unless $ARGV[0] =~ /^-/;
Note the LIST is prepended whole, not one element at a time, so the
prepended elements stay in the same order. Use C<reverse> to do the
except that Module I<must> be a bareword.
-VERSION, which can be specified as a literal of the form v5.6.1, demands
-that the current version of Perl (C<$^V> or $PERL_VERSION) be at least
-as recent as that version. (For compatibility with older versions of Perl,
-a numeric literal will also be interpreted as VERSION.) If the version
-of the running Perl interpreter is less than VERSION, then an error
-message is printed and Perl exits immediately without attempting to
-parse the rest of the file. Compare with L</require>, which can do a
-similar check at run time.
+VERSION may be either a numeric argument such as 5.006, which will be
+compared to C<$]>, or a literal of the form v5.6.1, which will be compared
+to C<$^V> (aka $PERL_VERSION. A fatal error is produced if VERSION is
+greater than the version of the current Perl interpreter; Perl will not
+attempt to parse the rest of the file. Compare with L</require>, which can
+do a similar check at run time.
+
+Specifying VERSION as a literal of the form v5.6.1 should generally be
+avoided, because it leads to misleading error messages under earlier
+versions of Perl which do not support this syntax. The equivalent numeric
+version should be used instead.
use v5.6.1; # compile time version check
use 5.6.1; # ditto
- use 5.005_03; # float version allowed for compatibility
+ use 5.006_001; # ditto; preferred for backwards compatibility
This is often useful if you need to check the current Perl version before
C<use>ing library modules that have changed in incompatible ways from
C<use> will call the VERSION method in class Module with the given
version as an argument. The default VERSION method, inherited from
the UNIVERSAL class, croaks if the given version is larger than the
-value of the variable C<$Module::VERSION>.
+value of the variable C<$Module::VERSION>.
Again, there is a distinction between omitting LIST (C<import> called
with no arguments) and an explicit empty LIST C<()> (C<import> not
use strict qw(subs vars refs);
use subs qw(afunc blurfl);
use warnings qw(all);
+ use sort qw(stable _quicksort _mergesort);
Some of these pseudo-modules import semantics into the current
block scope (like C<strict> or C<integer>, unlike ordinary modules,
If no C<unimport> method can be found the call fails with a fatal error.
-See L<perlmod> for a list of standard modules and pragmas. See L<perlrun>
+See L<perlmodlib> for a list of standard modules and pragmas. See L<perlrun>
for the C<-M> and C<-m> command-line options to perl that give C<use>
functionality from the command-line.
$now = time;
utime $now, $now, @ARGV;
+If the first two elements of the list are C<undef>, then the utime(2)
+function in the C library will be called with a null second argument.
+On most systems, this will set the file's access and modification
+times to the current time. (i.e. equivalent to the example above.)
+
+ utime undef, undef, @ARGV;
+
=item values HASH
Returns a list consisting of all the values of the named hash. (In a
be a power of two from 1 to 32 (or 64, if your platform supports
that).
-If BITS is 8, "elements" coincide with bytes of the input string.
+If BITS is 8, "elements" coincide with bytes of the input string.
If BITS is 16 or more, bytes of the input string are grouped into chunks
of size BITS/8, and each group is converted to a number as with
#!/usr/bin/perl -wl
print <<'EOT';
- 0 1 2 3
+ 0 1 2 3
unpack("V",$_) 01234567890123456789012345678901
------------------------------------------------------------------
EOT
Regardless of the machine architecture on which it is run, the above
example should print the following table:
- 0 1 2 3
+ 0 1 2 3
unpack("V",$_) 01234567890123456789012345678901
------------------------------------------------------------------
vec($_, 0, 1) = 1 == 1 10000000000000000000000000000000
use POSIX ":sys_wait_h";
#...
- do {
- $kid = waitpid(-1,&WNOHANG);
- } until $kid == -1;
+ do {
+ $kid = waitpid(-1, WNOHANG);
+ } until $kid > 0;
then you can do a non-blocking wait for all pending zombie processes.
Non-blocking wait is available on machines supporting either the