C<-I<X>>, C<chdir>, C<chmod>, C<chown>, C<chroot>, C<fcntl>, C<glob>,
C<ioctl>, C<link>, C<lstat>, C<mkdir>, C<open>, C<opendir>,
-C<readlink>, C<rename>, C<rmdir>, C<stat>, C<symlink>, C<umask>,
-C<unlink>, C<utime>
+C<readlink>, C<rename>, C<rmdir>, C<stat>, C<symlink>, C<sysopen>,
+C<umask>, C<unlink>, C<utime>
=item Keywords related to the control flow of your perl program
C<accept>, C<bind>, C<connect>, C<getpeername>, C<getsockname>,
C<getsockopt>, C<listen>, C<recv>, C<send>, C<setsockopt>, C<shutdown>,
-C<sockatmark>, C<socket>, C<socketpair>
+C<socket>, C<socketpair>
=item System V interprocess communication functions
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<sockatmark>, C<socket>, C<socketpair>,
+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<utime>, C<wait>, C<waitpid>
-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:
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 $a || -w _ || -x _;
packed address of the appropriate type for the socket. See the examples in
L<perlipc/"Sockets: Client/Server Communication">.
-=item binmode FILEHANDLE, DISCIPLINE
+=item binmode FILEHANDLE, LAYER
=item binmode FILEHANDLE
-Arranges for FILEHANDLE to be read or written in "binary" or "text" mode
-on systems where the run-time libraries distinguish between binary and
-text files. If FILEHANDLE is an expression, the value is taken as the
-name of the filehandle. DISCIPLINE can be either of C<:raw> for
-binary mode or C<:crlf> for "text" mode. If the DISCIPLINE is
-omitted, it defaults to C<:raw>. Returns true on success, C<undef> on
-failure. The C<:raw> are C<:clrf>, and any other directives of the
-form C<:...>, are called I/O I<disciplines>.
-
-The C<open> pragma can be used to establish default I/O disciplines.
-See L<open>.
+Arranges for FILEHANDLE to be read or written in "binary" or "text"
+mode on systems where the run-time libraries distinguish between
+binary and text files. If FILEHANDLE is an expression, the value is
+taken as the name of the filehandle. Returns true on success,
+otherwise it returns C<undef> and sets C<$!> (errno).
+
+If LAYER is omitted or specified as C<:raw> the filehandle is made
+suitable for passing binary data. This includes turning off possible CRLF
+translation and marking it as bytes (as opposed to Unicode characters).
+Note that as desipite what may be implied in I<"Programming Perl">
+(the Camel) or elsewhere C<:raw> is I<not> the simply inverse of C<:crlf>
+-- other layers which would affect binary nature of the stream are
+I<also> disabled. See L<PerlIO>, L<perlrun> and the discussion about the
+PERLIO environment variable.
+
+I<The LAYER parameter of the binmode() function is described as "DISCIPLINE"
+in "Programming Perl, 3rd Edition". However, since the publishing of this
+book, by many known as "Camel III", the consensus of the naming of this
+functionality has moved from "discipline" to "layer". All documentation
+of this version of Perl therefore refers to "layers" rather than to
+"disciplines". Now back to the regularly scheduled documentation...>
+
+On some systems (in general, DOS and Windows-based 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
+(like for example images).
+
+If LAYER is present it is a single string, but may contain
+multiple directives. The directives alter the behaviour of the
+file handle. When LAYER is present using binmode on text
+file makes sense.
+
+To mark FILEHANDLE as UTF-8, use C<:utf8>.
+
+The C<:bytes>, C<:crlf>, and C<:utf8>, and any other directives of the
+form C<:...>, are called I/O I<layers>. The C<open> pragma can be used to
+establish default I/O layers. See L<open>.
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
+is done on the filehandle. Calling binmode() will normally flush any
+pending buffered output data (and perhaps pending input data) on the
+handle. An exception to this is the C<:encoding> layer that
+changes the default character encoding of the handle, see L<open>.
+The C<:encoding> layer sometimes needs to be called in
mid-stream, and it doesn't flush the stream.
-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 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
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.
+on Unix and most VMS files). 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.
C<require> or C<use> statement, $evaltext contains the text of the
C<eval EXPR> statement. In particular, for an C<eval BLOCK> statement,
$filename is C<(eval)>, but $evaltext is undefined. (Note also that
-each C<use> statement creates a C<require> frame inside an C<eval EXPR>)
-frame. C<$hasargs> is true if a new instance of C<@_> was set up for the
-frame. C<$hints> and C<$bitmask> contain pragmatic hints that the caller
-was compiled with. The C<$hints> and C<$bitmask> values are subject to
-change between versions of Perl, and are not meant for external use.
+each C<use> statement creates a C<require> frame inside an C<eval EXPR>
+frame.) $subroutine may also be C<(unknown)> if this particular
+subroutine happens to have been deleted from the symbol table.
+C<$hasargs> is true if a new instance of C<@_> was set up for the frame.
+C<$hints> and C<$bitmask> contain pragmatic hints that the caller was
+compiled with. The C<$hints> and C<$bitmask> values are subject to change
+between versions of Perl, and are not meant for external use.
Furthermore, when called from within the DB package, caller returns more
detailed information: it sets the list variable C<@DB::args> to be the
If you chomp a list, each element is chomped, and the total number of
characters removed is returned.
+Note that parentheses are necessary when you're chomping anything
+that is not a simple variable. This is because C<chomp $cwd = `pwd`;>
+is interpreted as C<(chomp $cwd) = `pwd`;>, rather than as
+C<chomp( $cwd = `pwd` )> which you might expect. Similarly,
+C<chomp $a, $b> is interpreted as C<chomp($a), $b> rather than
+as C<chomp($a, $b)>.
+
=item chop VARIABLE
=item chop( LIST )
Note that C<chop> returns the last character. To return all but the last
character, use C<substr($string, 0, -1)>.
+See also L</chomp>.
+
=item chown LIST
Changes the owner (and group) of a list of files. The first two
on your favorite CPAN mirror for a slew of potentially useful
modules.
-If using crypt() on a Unicode string (which potentially has
-characters with codepoints above 255), Perl tries to make sense of
-the situation by using only the low eight bits of the characters when
-calling crypt().
+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
die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news';
chdir '/usr/spool/news' or die "Can't cd to spool: $!\n"
-If the value of EXPR does not end in a newline, the current script line
-number and input line number (if any) are also printed, and a newline
-is supplied. Note that the "input line number" (also known as "chunk")
-is subject to whatever notion of "line" happens to be currently in
-effect, and is also available as the special variable C<$.>.
-See L<perlvar/"$/"> and L<perlvar/"$.">.
+If the last element of LIST 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. Note that the "input line number" (also
+known as "chunk") is subject to whatever notion of "line" happens to
+be currently in effect, and is also available as the special variable
+C<$.>. See L<perlvar/"$/"> and L<perlvar/"$.">.
-Hint: sometimes appending C<", stopped"> to your message
-will cause it to make better sense when the string C<"at foo line 123"> is
-appended. Suppose you are running script "canasta".
+Hint: sometimes appending C<", stopped"> to your message will cause it
+to make better sense when the string C<"at foo line 123"> is appended.
+Suppose you are running script "canasta".
die "/etc/games is no good";
die "/etc/games is no good, stopped";
If LIST is empty and C<$@> 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 { $@->PROPAGATE(__FILE__, __LINE__) };>>
+C<$@>. ie. as if C<<$@ = eval { $@->PROPAGATE(__FILE__, __LINE__) };>>
were called.
If C<$@> is empty then the string C<"Died"> is used.
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
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
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>)
C<eval BLOCK> does I<not> count as a loop, so the loop control statements
C<next>, C<last>, or C<redo> cannot be used to leave or restart the block.
+Note that as a very special case, an C<eval ''> executed within the C<DB>
+package doesn't see the usual surrounding lexical scope, but rather the
+scope of the first non-DB piece of code that called it. You don't normally
+need to worry about this unless you are writing a Perl debugger.
+
=item exec LIST
=item exec PROGRAM LIST
second--glance appear to be an lvalue context may be fixed in a future
release.
-See L<perlref/"Pseudo-hashes: Using an array as a hash"> for specifics
-on how exists() acts when used on a pseudo-hash.
-
Use of a subroutine call, rather than a subroutine name, as an argument
to exists() is an error.
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)
=item getc
Returns the next character from the input file attached to FILEHANDLE,
-or the undefined value at end of file, or if there was an error.
-If FILEHANDLE is omitted, reads from STDIN. This is not particularly
-efficient. However, it cannot be used by itself to fetch single
-characters without waiting for the user to hit enter. For that, try
-something more like:
+or the undefined value at end of file, or if there was an error (in
+the latter case C<$!> is set). If FILEHANDLE is omitted, reads from
+STDIN. This is not particularly efficient. However, it cannot be
+used by itself to fetch single characters without waiting for the user
+to hit enter. For that, try something more like:
if ($BSD_STYLE) {
system "stty cbreak </dev/tty >/dev/tty 2>&1";
Returns the process id of the parent process.
+Note for Linux users: on Linux, the C functions C<getpid()> and
+C<getppid()> return different values from different threads. In order to
+be portable, this behavior is not reflected by the perl-level function
+C<getppid()>, that returns a consistent value across threads. If you want
+to call the underlying C<getppid()>, you may use the CPAN module
+C<Linux::Pid>.
+
=item getpriority WHICH,WHO
Returns the current priority for a process, a process group, or a user.
$name = getpwuid($num);
$name = getpwent();
$gid = getgrnam($name);
- $name = getgrgid($num;
+ $name = getgrgid($num);
$name = getgrent();
#etc.
=item glob
-Returns the value of EXPR with filename expansions such as the
-standard Unix shell F</bin/csh> would do. This is the internal function
-implementing the C<< <*.c> >> operator, but you can use it directly.
-If EXPR is omitted, C<$_> is used. The C<< <*.c> >> operator is
-discussed in more detail in L<perlop/"I/O Operators">.
+In list context, returns a (possibly empty) list of filename expansions on
+the value of EXPR such as the standard Unix shell F</bin/csh> would do. In
+scalar context, glob iterates through such filename expansions, returning
+undef when the list is exhausted. This is the internal function
+implementing the C<< <*.c> >> operator, but you can use it directly. If
+EXPR is omitted, C<$_> is used. The C<< <*.c> >> operator is discussed in
+more detail in L<perlop/"I/O Operators">.
Beginning with v5.6.0, this operator is implemented using the standard
C<File::Glob> extension. See L<File::Glob> for details.
=item lock THING
-This function places an advisory lock on a variable, subroutine,
-or referenced object contained in I<THING> until the lock goes out
-of scope. This is a built-in function only if your version of Perl
-was built with threading enabled, and if you've said C<use Thread>.
-Otherwise a user-defined function by this name will be called.
-See L<Thread>.
+This function places an advisory lock on a shared variable, or referenced
+object contained in I<THING> until the lock goes out of scope.
+
+lock() is a "weak keyword" : this means that if you've defined a function
+by this name (before any calls to it), that function will be called
+instead. (However, if you've said C<use threads>, lock() is always a
+keyword.) See L<threads>.
=item log EXPR
Does the same thing as the C<stat> function (including setting the
special C<_> filehandle) but stats a symbolic link instead of the file
the symbolic link points to. If symbolic links are unimplemented on
-your system, a normal C<stat> is done.
+your system, a normal C<stat> is done. For much more detailed
+information, please see the documentation for C<stat>.
If EXPR is omitted, stats C<$_>.
=item my EXPR
-=item my EXPR : ATTRIBUTES
+=item my TYPE EXPR
+
+=item my EXPR : ATTRS
+
+=item my TYPE EXPR : ATTRS
A C<my> declares the listed variables to be local (lexically) to the
-enclosing block, file, or C<eval>. If
-more than one value is listed, the list must be placed in parentheses. See
-L<perlsub/"Private Variables via my()"> for details.
+enclosing block, file, or C<eval>. If more than one value is listed,
+the list must be placed in parentheses.
+
+The exact semantics and interface of TYPE and ATTRS are still
+evolving. TYPE is currently bound to the use of C<fields> pragma,
+and attributes are handled using the C<attributes> pragma, or starting
+from Perl 5.8.0 also via the C<Attribute::Handlers> module. See
+L<perlsub/"Private Variables via my()"> for details, and L<fields>,
+L<attributes>, and L<Attribute::Handlers>.
=item next LABEL
See also L</continue> for an illustration of how C<last>, C<next>, and
C<redo> work.
+=item no Module VERSION LIST
+
+=item no Module VERSION
+
=item no Module LIST
+=item no Module
+
See the L</use> function, which C<no> is the opposite of.
=item oct EXPR
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.)
+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
In the 2-arguments (and 1-argument) form opening C<'-'> opens STDIN
and opening C<< '>-' >> opens STDOUT.
-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
-
+You may use the three-argument form of open to specify IO "layers"
+(sometimes also referred to as "disciplines") to be applied to the handle
+that affect how the input and output are processed (see L<open> and
+L<PerlIO> for more details). For example
+
open(FH, "<:utf8", "file")
will open the UTF-8 encoded file containing Unicode characters,
-see L<perluniintro>.
+see L<perluniintro>. (Note that if layers are specified in the
+three-arg form then default layers set by the C<open> pragma are
+ignored.)
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
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
+like Unix, Mac OS, and Plan 9, 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
C<die>. Even if C<die> won't do what you want (say, in a CGI script,
File handles can be opened to "in memory" files held in Perl scalars via:
- open($fh,'>', \$variable) || ..
+ open($fh, '>', \$variable) || ..
+
+Though if you try to re-open C<STDOUT> or C<STDERR> as an "in memory"
+file, you have to close it first:
+
+ close STDOUT;
+ open STDOUT, '>', \$variable or die "Can't open STDOUT: $!";
Examples:
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:
+Here is a script that saves, redirects, and restores C<STDOUT> and
+C<STDERR> using various methods:
#!/usr/bin/perl
- open(my $oldout, ">&", \*STDOUT);
- open(OLDERR, ">&STDERR");
+ open my $oldout, ">&STDOUT" or die "Can't dup STDOUT: $!";
+ open OLDERR, ">&", \*STDERR or die "Can't dup STDERR: $!";
- open(STDOUT, '>', "foo.out") || die "Can't redirect stdout";
- open(STDERR, ">&STDOUT") || die "Can't dup stdout";
+ open STDOUT, '>', "foo.out" or die "Can't redirect STDOUT: $!";
+ open STDERR, ">&STDOUT" or die "Can't dup STDOUT: $!";
- select(STDERR); $| = 1; # make unbuffered
- select(STDOUT); $| = 1; # make unbuffered
+ select STDERR; $| = 1; # make unbuffered
+ select STDOUT; $| = 1; # make unbuffered
print STDOUT "stdout 1\n"; # this works for
print STDERR "stderr 1\n"; # subprocesses too
- close(STDOUT);
- close(STDERR);
+ close STDOUT;
+ close STDERR;
- open(STDOUT, ">&OLDOUT");
- open(STDERR, ">&OLDERR");
+ open STDOUT, ">&", $oldout or die "Can't dup \$oldout: $!";
+ open STDERR, ">&OLDERR" or die "Can't dup OLDERR: $!";
print STDOUT "stdout 2\n";
print STDERR "stderr 2\n";
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.
+not yet supported on all platforms. A good rule of thumb is that if
+your platform has true C<fork()> (in other words, if your platform is
+UNIX) you can use the list form.
See L<perlipc/"Safe Pipe Opens"> for more examples of this.
=item our EXPR
-=item our EXPR : ATTRIBUTES
+=item our EXPR TYPE
+
+=item our EXPR : ATTRS
+
+=item our TYPE EXPR : ATTRS
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
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:
+with it.
+
+The exact semantics and interface of TYPE and ATTRS are still
+evolving. TYPE is currently bound to the use of C<fields> pragma,
+and attributes are handled using the C<attributes> pragma, or starting
+from Perl 5.8.0 also via the C<Attribute::Handlers> module. See
+L<perlsub/"Private Variables via my()"> for details, and L<fields>,
+L<attributes>, and L<Attribute::Handlers>.
+
+The only currently recognized C<our()> 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.) Examples:
our @EXPORT : unique = qw(foo);
our %EXPORT_TAGS : unique = (bar => [qw(aa bb cc)]);
our $VERSION : unique = "1.00";
+Note that this attribute also has the effect of making the global
+readonly when the first new interpreter is cloned (for example,
+when the first new thread is created).
+
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
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 A text (ASCII) string, will be space padded.
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).
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>,
=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) would be ordered natively
=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 *
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, 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>.
+omitted, the value C<1> is used. Currently EXPR with the value C<0> is
+also special-cased as C<1> - this has not been documented before perl 5.8.0
+and is subject to change in future versions of perl. 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,
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>.
+actually read, C<0> at end of file, or undef if there was an error (in
+the latter case C<$!> is also set). 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>
+been opened with the C<:utf8> I/O layer (see L</open>, and the C<open>
pragma, L<open>), the I/O will operate on characters, not bytes.
=item readdir DIRHANDLE
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>
+binmode() to operate with the C<:utf8> I/O layer (see the C<open>
pragma, L<open>), the I/O will operate on characters, not bytes.
=item redo LABEL
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
+layer), 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
select(undef, undef, undef, 0.25);
+Note that whether C<select> gets restarted after signals (say, SIGALRM)
+is implementation-dependent.
+
B<WARNING>: One should not attempt to mix buffered I/O (like C<read>
or <FH>) with C<select>, except as permitted by POSIX, and even
then only on POSIX systems. You have to use C<sysread> instead.
=item send SOCKET,MSG,FLAGS
-Sends a message on a socket. Attemps to send the scalar MSG to the
+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
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
+binmode() to operate with the C<:utf8> I/O layer (see L</open>, or
the C<open> pragma, L<open>), the I/O will operate on characters, not
bytes.
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
=item sort LIST
-Sorts the LIST and returns the sorted list value. If SUBNAME or BLOCK
-is omitted, C<sort>s 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 C<0>, depending on how the elements
-of the list are to be ordered. (The C<< <=> >> and C<cmp>
-operators are extremely useful in such routines.) SUBNAME may be a
-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 list context, this sorts the LIST and returns the sorted list value.
+In scalar context, the behaviour of C<sort()> is undefined.
+
+If SUBNAME or BLOCK is omitted, C<sort>s 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 C<0>,
+depending on how the elements of the list are to be ordered. (The C<<
+<=> >> and C<cmp> operators are extremely useful in such routines.)
+SUBNAME may be a 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.
If the subroutine's prototype is C<($$)>, the elements to be compared
are passed by reference in C<@_>, as for a normal subroutine. This is
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>.
+independent ways quite probably will. See L<sort>.
Examples:
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 );
+ # force use of mergesort (not portable outside Perl 5.8)
+ use sort '_mergesort'; # note discouraging _
@new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;
If you're using strict, you I<must not> declare $a
removed. The array grows or shrinks as necessary.
If OFFSET is negative then it starts that far from the end of the array.
If LENGTH is omitted, removes everything from OFFSET onward.
-If LENGTH is negative, leaves that many elements off the end of the array.
-If both OFFSET and LENGTH are omitted, removes everything.
+If LENGTH is negative, removes the elements from OFFSET onward
+except for -LENGTH elements at the end of the array.
+If both OFFSET and LENGTH are omitted, removes everything. If OFFSET is
+past the end of the array, perl issues a warning, and splices at the
+end of the array.
The following equivalences hold (assuming C<$[ == 0>):
not be confused with the use of C<//> to mean "the last successful pattern
match".
-Empty leading (or trailing) fields are produced when there positive width
+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:
patterns that vary at runtime. (To do runtime compilation only once,
use C</$variable/o>.)
-As a special case, specifying a PATTERN of space (C<' '>) will split on
-white space just as C<split> with no arguments does. Thus, C<split(' ')> can
-be used to emulate B<awk>'s default behavior, whereas C<split(/ /)>
+As a special case, specifying a PATTERN of space (S<C<' '>>) will split on
+white space just as C<split> with no arguments does. Thus, S<C<split(' ')>> can
+be used to emulate B<awk>'s default behavior, whereas S<C<split(/ /)>>
will give you as many null initial fields as there are leading spaces.
-A C<split> on C</\s+/> is like a C<split(' ')> except that any leading
+A C<split> on C</\s+/> is like a S<C<split(' ')>> except that any leading
whitespace produces a null first field. A C<split> with no arguments
-really does a C<split(' ', $_)> internally.
+really does a S<C<split(' ', $_)>> internally.
A PATTERN of C</^/> is treated as if it were C</^/m>, since it isn't
much use otherwise.
%O a synonym for %lo
%F a synonym for %f
-Note that the number of exponent digits in the scientific notation by
-C<%e>, C<%E>, C<%g> and C<%G> for numbers with the modulus of the
+Note that the number of exponent digits in the scientific notation produced
+by C<%e>, C<%E>, C<%g> and C<%G> for numbers with the modulus of the
exponent less than 100 is system-dependent: it may be three or less
(zero-padded as necessary). In other words, 1.23 times ten to the
99th may be either "1.23e99" or "1.23e099".
-Perl permits the following universally-known flags between the C<%>
-and the conversion letter:
+Between the C<%> and the format letter, you may specify a number of
+additional attributes controlling the interpretation of the format.
+In order, these are:
+
+=over 4
+
+=item format parameter index
+
+An explicit format parameter index, such as C<2$>. By default sprintf
+will format the next unused argument in the list, but this allows you
+to take the arguments out of order. Eg:
+ printf '%2$d %1$d', 12, 34; # prints "34 12"
+ printf '%3$d %d %1$d', 1, 2, 3; # prints "3 1 1"
+
+=item flags
+
+one or more of:
space prefix positive number with a space
+ prefix positive number with a plus sign
- left-justify within the field
0 use zeros, not spaces, to right-justify
- # 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
- l interpret integer as C type "long" or "unsigned long"
- h interpret integer as C type "short" or "unsigned short"
- If no flags, interpret integer as C type "int" or "unsigned"
-
-Perl supports parameter ordering, in other words, fetching the
-parameters in some explicitly specified "random" ordering as opposed
-to the default implicit sequential ordering. The syntax is, instead
-of the C<%> and C<*>, to use C<%>I<digits>C<$> and C<*>I<digits>C<$>,
-where the I<digits> is the wanted index, from one upwards. For example:
-
- printf "%2\$d %1\$d\n", 12, 34; # will print "34 12\n"
- printf "%*2\$d\n", 12, 3; # will print " 12\n"
-
-Note that using the reordering syntax does not interfere with the usual
-implicit sequential fetching of the parameters:
-
- printf "%2\$d %d\n", 12, 34; # will print "34 12\n"
- printf "%2\$d %d %d\n", 12, 34; # will print "34 12 34\n"
- printf "%3\$d %d %d\n", 12, 34, 56; # will print "56 12 34\n"
- printf "%2\$*3\$d %d\n", 12, 34, 3; # will print " 34 12\n"
- printf "%*3\$2\$d %d\n", 12, 34, 3; # will print " 34 12\n"
-
-There are also two Perl-specific flags:
-
- V interpret integer as Perl's standard integer type
- 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 "*"
-
-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).
+ # prefix non-zero octal with "0", non-zero hex with "0x",
+ non-zero binary with "0b"
+
+For example:
+
+ printf '<% d>', 12; # prints "< 12>"
+ printf '<%+d>', 12; # prints "<+12>"
+ printf '<%6s>', 12; # prints "< 12>"
+ printf '<%-6s>', 12; # prints "<12 >"
+ printf '<%06s>', 12; # prints "<000012>"
+ printf '<%#x>', 12; # prints "<0xc>"
+
+=item vector flag
+
+The vector flag C<v>, optionally specifying the join string to use.
+This flag tells perl to interpret the supplied string as a vector
+of integers, one for each character in the string, separated by
+a given string (a dot C<.> by default). This can be useful for
+displaying ordinal values of characters in arbitrary strings:
+
+ printf "version is v%vd\n", $^V; # Perl's version
+
+Put an asterisk C<*> before the C<v> to override the string to
+use to separate the numbers:
+
+ printf "address is %*vX\n", ":", $addr; # IPv6 address
+ printf "bits are %0*v8b\n", " ", $bits; # random bitstring
+
+You can also explicitly specify the argument number to use for
+the join string using eg C<*2$v>:
+
+ printf '%*4$vX %*4$vX %*4$vX', @addr[1..3], ":"; # 3 IPv6 addresses
+
+=item (minimum) width
+
+Arguments are usually formatted to be only as wide as required to
+display the given value. You can override the width by putting
+a number here, or get the width from the next argument (with C<*>)
+or from a specified argument (with eg C<*2$>):
+
+ printf '<%s>', "a"; # prints "<a>"
+ printf '<%6s>', "a"; # prints "< a>"
+ printf '<%*s>', 6, "a"; # prints "< a>"
+ printf '<%*2$s>', "a", 6; # prints "< a>"
+ printf '<%2s>', "long"; # prints "<long>" (does not truncate)
+
If a field width obtained through C<*> is negative, it has the same
effect as the C<-> flag: left-justification.
-The C<v> flag is useful for displaying ordinal values of characters
-in arbitrary strings:
+=item precision, or maximum width
- printf "version is v%vd\n", $^V; # Perl's version
- printf "address is %*vX\n", ":", $addr; # IPv6 address
- printf "bits are %*vb\n", " ", $bits; # random bitstring
+You can specify a precision (for numeric conversions) or a maximum
+width (for string conversions) by specifying a C<.> followed by a number.
+For floating point formats, with the exception of 'g' and 'G', this specifies
+the number of decimal places to show (the default being 6), eg:
-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>.
+ # these examples are subject to system-specific variation
+ printf '<%f>', 1; # prints "<1.000000>"
+ printf '<%.1f>', 1; # prints "<1.0>"
+ printf '<%.0f>', 1; # prints "<1>"
+ printf '<%e>', 10; # prints "<1.000000e+01>"
+ printf '<%.1e>', 10; # prints "<1.0e+01>"
-If Perl understands "quads" (64-bit integers) (this requires
-either that the platform natively support quads or that Perl
-be specifically compiled to support quads), the characters
+For 'g' and 'G', this specifies the maximum number of digits to show,
+including prior to the decimal point as well as after it, eg:
- d u o x X b i D U O
+ # these examples are subject to system-specific variation
+ printf '<%g>', 1; # prints "<1>"
+ printf '<%.10g>', 1; # prints "<1>"
+ printf '<%g>', 100; # prints "<100>"
+ printf '<%.1g>', 100; # prints "<1e+02>"
+ printf '<%.2g>', 100.01; # prints "<1e+02>"
+ printf '<%.5g>', 100.01; # prints "<100.01>"
+ printf '<%.4g>', 100.01; # prints "<100>"
-print quads, and they may optionally be preceded by
+For integer conversions, specifying a precision implies that the
+output of the number itself should be zero-padded to this width:
- ll L q
+ printf '<%.6x>', 1; # prints "<000001>"
+ printf '<%#.6x>', 1; # prints "<0x000001>"
+ printf '<%-10.6x>', 1; # prints "<000001 >"
-For example
+For string conversions, specifying a precision truncates the string
+to fit in the specified width:
- %lld %16LX %qo
+ printf '<%.5s>', "truncated"; # prints "<trunc>"
+ printf '<%10.5s>', "truncated"; # prints "< trunc>"
-You can find out whether your Perl supports quads via L<Config>:
+You can also get the precision from the next argument using C<.*>:
- use Config;
- ($Config{use64bitint} eq 'define' || $Config{longsize} == 8) &&
- print "quads\n";
+ printf '<%.6x>', 1; # prints "<000001>"
+ printf '<%.*x>', 6, 1; # prints "<000001>"
-If Perl understands "long doubles" (this requires that the platform
-support long doubles), the flags
+You cannot currently get the precision from a specified number,
+but it is intended that this will be possible in the future using
+eg C<.*2$>:
- e f g E F G
+ printf '<%.*2$x>', 1, 6; # INVALID, but in future will print "<000001>"
-may optionally be preceded by
+=item size
- ll L
+For numeric conversions, you can specify the size to interpret the
+number as using C<l>, C<h>, C<V>, C<q>, C<L>, or C<ll>. For integer
+conversions (C<d u o x X b i D U O>), numbers are usually assumed to be
+whatever the default integer size is on your platform (usually 32 or 64
+bits), but you can override this to use instead one of the standard C types,
+as supported by the compiler used to build Perl:
-For example
+ l interpret integer as C type "long" or "unsigned long"
+ h interpret integer as C type "short" or "unsigned short"
+ q, L or ll interpret integer as C type "long long", "unsigned long long".
+ or "quads" (typically 64-bit integers)
- %llf %Lg
+The last will produce errors if Perl does not understand "quads" in your
+installation. (This requires that either the platform natively supports quads
+or Perl was specifically compiled to support quads.) You can find out
+whether your Perl supports quads via L<Config>:
-You can find out whether your Perl supports long doubles via L<Config>:
+ use Config;
+ ($Config{use64bitint} eq 'define' || $Config{longsize} >= 8) &&
+ print "quads\n";
+
+For floating point conversions (C<e f g E F G>), numbers are usually assumed
+to be the default floating point size on your platform (double or long double),
+but you can force 'long double' with C<q>, C<L>, or C<ll> if your
+platform supports them. You can find out whether your Perl supports long
+doubles via L<Config>:
use Config;
$Config{d_longdbl} eq 'define' && print "long doubles\n";
+You can find out whether Perl considers 'long double' to be the default
+floating point size to use on your platform via L<Config>:
+
+ use Config;
+ ($Config{uselongdouble} eq 'define') &&
+ print "long doubles by default\n";
+
+It can also be the case that long doubles and doubles are the same thing:
+
+ use Config;
+ ($Config{doublesize} == $Config{longdblsize}) &&
+ print "doubles are long doubles\n";
+
+The size specifier C<V> has no effect for Perl code, but it is supported
+for compatibility with XS code; it means 'use the standard size for
+a Perl integer (or floating-point number)', which is already the
+default for Perl code.
+
+=item order of arguments
+
+Normally, sprintf takes the next unused argument as the value to
+format for each format specification. If the format specification
+uses C<*> to require additional arguments, these are consumed from
+the argument list in the order in which they appear in the format
+specification I<before> the value to format. Where an argument is
+specified using an explicit index, this does not affect the normal
+order for the arguments (even when the explicitly specified index
+would have been the next argument in any case).
+
+So:
+
+ printf '<%*.*s>', $a, $b, $c;
+
+would use C<$a> for the width, C<$b> for the precision and C<$c>
+as the value to format, while:
+
+ print '<%*1$.*s>', $a, $b;
+
+would use C<$a> for the width and the precision, and C<$b> as the
+value to format.
+
+Here are some more examples - beware that when using an explicit
+index, the C<$> may need to be escaped:
+
+ printf "%2\$d %d\n", 12, 34; # will print "34 12\n"
+ printf "%2\$d %d %d\n", 12, 34; # will print "34 12 34\n"
+ printf "%3\$d %d %d\n", 12, 34, 56; # will print "56 12 34\n"
+ printf "%2\$*3\$d %d\n", 12, 34, 3; # will print " 34 12\n"
+
+=back
+
+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>.
+
=item sqrt EXPR
=item sqrt
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.
+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
7 size total size of file, in bytes
8 atime last access time in seconds since the epoch
9 mtime last modify time in seconds since the epoch
- 10 ctime inode change time (NOT creation time!) in seconds since the epoch
+ 10 ctime inode change time in seconds since the epoch (*)
11 blksize preferred block size for file system I/O
12 blocks actual number of blocks allocated
(The epoch was at 00:00 January 1, 1970 GMT.)
+(*) The ctime field is non-portable, in particular you cannot expect
+it to be a "creation time", see L<perlport/"Files and Filesystems">
+for details.
+
If stat is passed the special filehandle consisting of an underline, no
stat is done, but the current contents of the stat structure from the
last stat or filetest are returned. Example:
$group_read = ($mode & S_IRGRP) >> 3;
$other_execute = $mode & S_IXOTH;
- printf "Permissions are %04o\n", S_ISMODE($mode), "\n";
+ printf "Permissions are %04o\n", S_IMODE($mode), "\n";
$is_setuid = $mode & S_ISUID;
$is_setgid = S_ISDIR($mode);
S_IRWXG S_IRGRP S_IWGRP S_IXGRP
S_IRWXO S_IROTH S_IWOTH S_IXOTH
- # Setuid/Setgid/Stickiness.
+ # Setuid/Setgid/Stickiness/SaveText.
+ # Note that the exact meaning of these is system dependent.
S_ISUID S_ISGID S_ISVTX S_ISTXT
and the S_IF* functions are
- S_IFMODE($mode) the part of $mode containing the permission bits
+ S_IMODE($mode) the part of $mode containing the permission bits
and the setuid/setgid/sticky bits
S_IFMT($mode) the part of $mode containing the file type
S_ISENFMT($mode) S_ISWHT($mode)
See your native chmod(2) and stat(2) documentation for more details
-about the S_* constants.
+about the S_* constants. To get status info for a symbolic link
+instead of the target file behind the link, use the C<lstat> function.
=item study SCALAR
print $file, "\n";
}
-=item sub BLOCK
+=item sub NAME BLOCK
-=item sub NAME
+=item sub NAME (PROTO) BLOCK
-=item sub NAME BLOCK
+=item sub NAME : ATTRS BLOCK
-This is subroutine definition, not a real function I<per se>. With just a
-NAME (and possibly prototypes or attributes), it's just a forward declaration.
-Without a NAME, it's an anonymous function declaration, and does actually
-return a value: the CODE ref of the closure you just created. See L<perlsub>
-and L<perlref> for details.
+=item sub NAME (PROTO) : ATTRS BLOCK
+
+This is subroutine definition, not a real function I<per se>.
+Without a BLOCK it's just a forward declaration. Without a NAME,
+it's an anonymous function declaration, and does actually return
+a value: the CODE ref of the closure you just created.
+
+See L<perlsub> and L<perlref> for details about subroutines and
+references, and L<attributes> and L<Attribute::Handlers> for more
+information about attributes.
=item substr EXPR,OFFSET,LENGTH,REPLACEMENT
=item sysread FILEHANDLE,SCALAR,LENGTH
-Attempts to read LENGTH I<characters> of data into variable SCALAR from
-the specified FILEHANDLE, using the system call read(2). It bypasses
-buffered IO, so mixing this with other kinds of reads, C<print>,
-C<write>, C<seek>, C<tell>, or C<eof> can cause confusion because
-stdio usually buffers data. Returns the number of characters actually
-read, C<0> at end of file, or undef if there was an error. SCALAR
-will be grown or shrunk so that the last byte actually read is the
-last byte of the scalar after the read.
+Attempts to read LENGTH I<characters> of data into variable SCALAR
+from the specified FILEHANDLE, using the system call read(2). It
+bypasses buffered IO, so mixing this with other kinds of reads,
+C<print>, C<write>, C<seek>, C<tell>, or C<eof> can cause confusion
+because stdio usually buffers data. Returns the number of characters
+actually read, C<0> at end of file, or undef if there was an error (in
+the latter case C<$!> is also set). 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>
+been opened with the C<:utf8> I/O layer (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
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()
+on characters (for example by using the C<:utf8> I/O layer), tell()
will return byte offsets, not character offsets (because implementing
that would render sysseek() very slow).
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 = $? & 128;
+or more portably by using the W*() calls of the POSIX extension;
+see L<perlport> for more information.
+
When the arguments get executed via the system shell, results
and return codes will be subject to its quirks and capabilities.
See L<perlop/"`STRING`"> and L</exec> for details.
mixing this with reads (other than C<sysread())>, C<print>, C<write>,
C<seek>, C<tell>, or C<eof> may cause confusion because stdio usually
buffers data. Returns the number of characters actually written, or
-C<undef> if there was an error. If the LENGTH is greater than the
-available data in the SCALAR after the OFFSET, only as much data as is
-available will be written.
+C<undef> if there was an error (in this case the errno variable C<$!>
+is also set). 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
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
+been opened with the C<:utf8> I/O layer (see L</open>, and the open
pragma, L<open>), the I/O will operate on characters, not bytes.
=item tell FILEHANDLE
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
+layer), 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
=item time
Returns the number of non-leap seconds since whatever time the system
-considers to be the epoch (that's 00:00:00, January 1, 1904 for MacOS,
+considers to be the epoch (that's 00:00:00, January 1, 1904 for Mac OS,
and 00:00:00 UTC, January 1, 1970 for most other systems).
Suitable for feeding to C<gmtime> and C<localtime>.
on your system. Returns true if successful, the undefined value
otherwise.
+The behavior is undefined if LENGTH is greater than the length of the
+file.
+
=item uc EXPR
=item uc
=item untie VARIABLE
Breaks the binding between a variable and a package. (See C<tie>.)
+Has no effect if the variable is not tied.
=item unshift ARRAY,LIST
no strict 'refs';
no warnings;
-If no C<unimport> method can be found the call fails with a fatal error.
-
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.
projects / p5sagit/p5-mst-13.2.git / blobdiff