=item Functions for SCALARs or strings
X<scalar> X<string> X<character>
-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//>, C<qq//>, C<reverse>,
+C<chomp>, C<chop>, C<chr>, C<crypt>, C<fc>, C<hex>, C<index>, C<lc>,
+C<l
cfirst>, C<length>, C<oct>, C<ord>, C<pack>, C<q//>, C<qq//>, C<reverse>,
C<rindex>, C<sprintf>, C<substr>, C<tr///>, C<uc>, C<ucfirst>, C<y///>
+C<fc> is available only if the C<"fc"> feature is enabled or if it is
+prefixed with C<CORE::>. The C<"fc"> feature is enabled automatically
+with a C<use v5.16> (or higher) declaration in the current scope.
+
+
=item Regular expressions and pattern matching
X<regular expression> X<regex> X<regexp>
C<sysread>, C<sysseek>, C<syswrite>, C<tell>, C<telldir>, C<truncate>,
C<warn>, C<write>
+C<say> is available only if the C<"say"> feature is enabled or if it is
+prefixed with C<CORE::>. The C<"say"> feature is enabled automatically
+with a C<use v5.10> (or higher) declaration in the current scope.
+
=item Functions for fixed-length data or records
C<pack>, C<read>, C<syscall>, C<sysread>, C<syswrite>, C<unpack>, C<vec>
=item Keywords related to the control flow of your Perl program
X<control flow>
-C<caller>, C<continue>, C<die>, C<do>, C<dump>, C<eval>, C<exit>,
-C<goto>, C<last>, C<next>, C<redo>, C<return>, C<sub>, C<wantarray>
+C<caller>, C<continue>, C<die>, C<do>,
+C<dump>, C<eval>, C<evalbytes> C<exit>,
+C<__FILE__>, C<goto>, C<last>, C<__LINE__>, C<next>, C<__PACKAGE__>,
+C<redo>, C<return>, C<sub>, C<__SUB__>, C<wantarray>
+
+C<evalbytes> is only available with with the C<"evalbytes"> feature (see
+L<feature>) or if prefixed with C<CORE::>. C<__SUB__> is only available
+with with the C<"current_sub"> feature or if prefixed with C<CORE::>. Both
+the C<"evalbytes"> and C<"current_sub"> features are enabled automatically
+with a C<use v5.16> (or higher) declaration in the current scope.
=item Keywords related to the switch feature
-C<break>, C<continue>, C<default, >C<given>, C<when>
+C<break>, C<continue>, C<default>, C<given>, C<when>
-These are available only if you enable the C<"switch"> feature.
-See L<feature> and L<perlsyn/"Switch statements">.
-Alternately, include a C<use v5.10> or later to the current scope.
+Except for C<continue>, these are available only if you enable the
+C<"switch"> feature or use the C<CORE::> prefix. See L<feature> and
+L<perlsyn/"Switch Statements">. The C<"switch"> feature is enabled
+automatically with a C<use v5.10> (or higher) declaration in the current
+scope. In Perl 5.14 and earlier, C<continue> required the C<"switch">
+feature, like the other keywords.
=item Keywords related to scoping
C<caller>, C<import>, C<local>, C<my>, C<our>, C<package>, C<state>, C<use>
-C<state> is available only if the C<"state"> feature is enabled. See
-L<feature>. Alternately, include a C<use v5.10> or later to the current scope.
+C<state> is available only if the C<"state"> feature is enabled or if it is
+prefixed with C<CORE::>. The C<"state"> feature is enabled automatically
+with a C<use v5.10> (or higher) declaration in the current scope.
=item Miscellaneous functions
-C<defined>, C<dump>, C<eval>, C<formline>, C<local>, C<my>, C<our>,
+C<defined>, C<dump>, C<eval>, C<evalbytes>,
+C<formline>, C<local>, C<my>, C<our>,
C<reset>, C<scalar>, C<state>, C<undef>, C<wantarray>
=item Functions for processes and process groups
X<process> X<pid> X<process id>
C<alarm>, C<exec>, C<fork>, C<getpgrp>, C<getppid>, C<getpriority>, C<kill>,
-C<pipe>, C<qx//>, C<setpgrp>, C<setpriority>, C<sleep>, C<system>,
+C<pipe>, C<qx//>, C<readpipe>, C<setpgrp>,
+C<setpriority>, C<sleep>, C<system>,
C<times>, C<wait>, C<waitpid>
=item Keywords related to Perl modules
C<gmtime>, C<localtime>, C<time>, C<times>
-=item Functions new in perl5
-X<perl5>
-
-C<abs>, C<bless>, C<break>, C<chomp>, C<chr>, C<continue>, C<default>,
-C<exists>, C<formline>, C<given>, C<glob>, C<import>, C<lc>, C<lcfirst>,
-C<lock>, C<map>, C<my>, C<no>, C<our>, C<prototype>, C<qr//>, C<qw//>, C<qx//>,
-C<readline>, C<readpipe>, C<ref>, C<sub>*, C<sysopen>, C<tie>, C<tied>, C<uc>,
-C<ucfirst>, C<untie>, C<use>, C<when>
-
-* C<sub> was a keyword in Perl 4, but in Perl 5 it is an
-operator, which can be used in expressions.
+=item Non-function keywords
-=item Functions obsoleted in perl5
-
-C<dbmclose>, C<dbmopen>
+C<AUTOLOAD>, C<BEGIN>, C<CHECK>, C<CORE>, C<DESTROY>, C<END>, C<INIT>,
+C<UNITCHECK>, C<__DATA__>, C<__END__>, C<and>, C<cmp>, C<else>, C<elseif>,
+C<elsif>, C<eq>, C<for>, C<foreach>, C<ge>, C<gt>, C<if>, C<le>, C<lt>, C<ne>,
+C<not>, C<or>, C<unless>, C<until>, C<while>, C<x>, C<xor>
=back
following a minus are interpreted as file tests.
These operators are exempt from the "looks like a function rule" described
-above. That is, an opening parenthesis after the operator does not affect
-how much of the following code constitutes the argument. Put the opening
+above. That is, an opening parenthesis after the operator does not affect
+how much of the following code constitutes the argument. Put the opening
parentheses before the operator to separate it from code that follows (this
applies only to operators with higher precedence than unary operators, of
course):
access(2) family of system calls. Also note that the C<-x> and C<-X> may
under this pragma return true even if there are no execute permission
bits set (nor any extra execute permission ACLs). This strangeness is
-due to the underlying system calls' definitions. Note also that, due to
+due to the underlying system calls' definitions. Note also that, due to
the implementation of C<use filetest 'access'>, the C<_> special
filehandle won't cache the results of the file tests when this pragma is
in effect. Read the documentation for the C<filetest> pragma for more
As of Perl 5.9.1, as a form of purely syntactic sugar, you can stack file
test operators, in a way that C<-f -w -x $file> is equivalent to
-C<-x $file && -w _ && -f _>. (This is only fancy fancy: if you use
+C<-x $file && -w _ && -f _>. (This is only fancy fancy: if you use
the return value of C<-f $file> as an argument to another filetest
operator, no special magic will happen.)
Portability issues: L<perlport/-X>.
+To avoid confusing would-be users of your code with mysterious
+syntax errors, put something like this at the top of your script:
+
+ use 5.010; # so filetest ops can stack
+
=item abs VALUE
X<abs> X<absolute>
Arranges to have a SIGALRM delivered to this process after the
specified number of wallclock seconds has elapsed. If SECONDS is not
-specified, the value stored in C<$_> is used. (On some machines,
+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.)
distribution) provides ualarm(). You may also 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. See L<perlfaq8> for details.
+your system supports it.
See L<perlfaq8> for details.
It is usually a mistake to intermix C<alarm> and C<sleep> calls, because
C<sleep> may be internally implemented on your system with C<alarm>.
like images, for example.
If LAYER is present it is a single string, but may contain multiple
-directives. The directives alter the behaviour of the filehandle.
+directives. The directives alter the behaviour of the filehandle.
When LAYER is present, using binmode on a text file makes sense.
If LAYER is omitted or specified as C<:raw> the filehandle is made
-suitable for passing binary data. This includes turning off possible CRLF
+suitable for passing binary data. This includes turning off possible CRLF
translation and marking it as bytes (as opposed to Unicode characters).
Note that, despite what may be implied in I<"Programming Perl"> (the
Camel, 3rd edition) or elsewhere, C<:raw> is I<not> simply the inverse of C<:crlf>.
Other layers that would affect the binary nature of the stream are
-I<also> disabled. See L<PerlIO>, L<perlrun>, and the discussion about the
+I<also> disabled.
See L<PerlIO>, L<perlrun>, and the discussion about the
PERLIO environment variable.
The C<:bytes>, C<:crlf>, C<:utf8>, and any other directives of the
To mark FILEHANDLE as UTF-8, use C<:utf8> or C<:encoding(UTF-8)>.
C<:utf8> just marks the data as UTF-8 without further checking,
while C<:encoding(UTF-8)> checks the data for actually being valid
-UTF-8. More details can be found in L<PerlIO::encoding>.
+UTF-8.
More details can be found in L<PerlIO::encoding>.
In general, binmode() should be called after open() but before any I/O
is done on the filehandle. Calling binmode() normally flushes any
All variants of Unix, Mac OS (old and new), 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 old, pre-Darwin
-flavors of Mac OS, and is LINE FEED on Unix and most VMS files). In other
+flavors of Mac OS, and is LINE FEED 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
is used. Because a C<bless> is often the last thing in a constructor,
it returns the reference for convenience. Always use the two-argument
version if a derived class might inherit the function doing the blessing.
-See L<perltoot> and L<perlobj> for more about the blessing (and blessings)
-of objects.
+SeeL<perlobj> for more about the blessing (and blessings) of objects.
Consider always blessing objects in CLASSNAMEs that are mixed case.
Namespaces with all lowercase names are considered reserved for
-Perl pragmata. Builtin types have all uppercase names. To prevent
+Perl pragmata. Builtin types have all uppercase names. To prevent
confusion, you may wish to avoid such package names as well. Make sure
that CLASSNAME is a true value.
Break out of a C<given()> block.
This keyword is enabled by the C<"switch"> feature: see
-L<feature> for more information. Alternately, include a C<use
+L<feature> for more information. You can also access it by
+prefixing it with C<CORE::>. Alternately, include a C<use
v5.10> or later to the current scope.
=item caller EXPR
between versions of Perl, and are not meant for external use.
C<$hinthash> is a reference to a hash containing the value of C<%^H> when the
-caller was compiled, or C<undef> if C<%^H> was empty. Do not modify the values
+caller was compiled, or C<undef> if C<%^H> was empty. Do not modify the values
of this hash, as they are the actual values stored in the optree.
-Furthermore, when called from within the DB package, caller returns more
+Furthermore, when called from within the DB package in
+list context, and with an argument, caller returns more
detailed information: it sets the list variable C<@DB::args> to be the
arguments with which the subroutine was invoked.
previous time C<caller> was called.
Be aware that setting C<@DB::args> is I<best effort>, intended for
-debugging or generating backtraces, and should not be relied upon. In
+debugging or generating backtraces, and should not be relied upon. In
particular, as C<@_> contains aliases to the caller's arguments, Perl does
not take a copy of C<@_>, so C<@DB::args> will contain modifications the
subroutine makes to C<@_> or its contents, not the original values at call
-time. C<@DB::args>, like C<@_>, does not hold explicit references to its
+time. C<@DB::args>, like C<@_>, does not hold explicit references to its
elements, so under certain cases its elements may have become freed and
-reallocated for other variables or temporary values. Finally, a side effect
+reallocated for other variables or temporary values. Finally, a side effect
of the current implementation is that the effects of C<shift @_> can
I<normally> be undone (but not C<pop @_> or other splicing, I<and> not if a
reference to C<@_> has been taken, I<and> subject to the caveat about reallocated
elements), so C<@DB::args> is actually a hybrid of the current state and
-initial state of C<@_>. Buyer beware.
+initial state of C<@_>. Buyer beware.
=item chdir EXPR
X<chdir>
=item chdir
-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}>. (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 on 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$LOGIN}> is also checked, and used if it is set.) If
+neither is set, C<chdir> does nothing. It returns true on success,
+false otherwise. See the example under C<die>.
On systems that support fchdir(2), you may pass a filehandle or
directory handle as the argument. On systems that don't support fchdir(2),
You don't have to close FILEHANDLE if you are immediately going to do
another C<open> on it, because C<open> closes it for you. (See
-C<open>.) However, an explicit C<close> on an input file resets the line
+L<open|/open FILEHANDLE>.) However, an explicit C<close> on an input file resets the line
counter (C<$.>), while the implicit close done by C<open> does not.
If the filehandle came from a piped open, C<close> returns false if one of
=item continue
-C<continue> is actually a flow control statement rather than a function. If
+When followed by a BLOCK, C<continue> is actually a
+flow control statement rather than a function. If
there is a C<continue> BLOCK attached to a BLOCK (typically in a C<while> or
C<foreach>), it is always executed just before the conditional is about to
be evaluated again, just like the third part of a C<for> loop in C. Thus
empty one, logically enough, so C<next> goes directly back
to check the condition at the top of the loop.
-If the C<"switch"> feature is enabled, C<continue> is also a function that
+When there is no BLOCK, C<continue> is a function that
falls through the current C<when> or C<default> block instead of iterating
a dynamically enclosing C<foreach> or exiting a lexically enclosing C<given>.
-See L<feature> and L<perlsyn/"Switch statements"> for more
+In Perl 5.14 and earlier, this form of C<continue> was
+only available when the C<"switch"> feature was enabled.
+See L<feature> and L<perlsyn/"Switch Statements"> for more
information.
=item cos EXPR
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 PLAINTEXT mattered. But alternative
+the first eight bytes of PLAINTEXT mattered. But alternative
hashing schemes (like MD5), higher level security schemes (like C2),
and implementations on non-Unix platforms may produce different
strings.
=item dbmopen HASH,DBNAME,MASK
X<dbmopen> X<dbm> X<ndbm> X<sdbm> X<gdbm>
-[This function has been largely superseded by the C<tie> function.]
+[This function has been largely superseded by the
+L<tie|/tie VARIABLE,CLASSNAME,LIST> function.]
This binds a dbm(3), ndbm(3), sdbm(3), gdbm(3), or Berkeley DB file to a
hash. HASH is the name of the hash. (Unlike normal C<open>, the first
argument is I<not> a filehandle, even though it looks like one). DBNAME
is the name of the database (without the F<.dir> or F<.pag> extension if
any). If the database does not exist, it is created with protection
-specified by MASK (as modified by the C<umask>). If your system supports
+specified by MASK (as modified by the C<umask>). To prevent creation of
+the database if it doesn't exist, you may specify a MODE
+of 0, and the function will return a false value if it
+can't find an existing database. If your system supports
only the older DBM functions, you may make only one C<dbmopen> call in your
program. In older versions of Perl, if your system had neither DBM nor
ndbm, calling C<dbmopen> produced a fatal error; it now falls back to
Within a C<foreach> or a C<given>, a C<default> BLOCK acts like a C<when>
that's always true. Only available after Perl 5.10, and only if the
-C<switch> feature has been requested. See L</when>.
+C<switch> feature has been requested or if the keyword is prefixed with
+C<CORE::>. See L</when>.
=item defined EXPR
X<defined> X<undef> X<undefined>
=item die LIST
X<die> X<throw> X<exception> X<raise> X<$@> X<abort>
-C<die> raises an exception. Inside an C<eval> the error message is stuffed
+C<die> raises an exception. Inside an C<eval> the error message is stuffed
into C<$@> and the C<eval> is terminated with the undefined value.
If the exception is outside of all enclosing C<eval>s, then the uncaught
-exception prints LIST to C<STDERR> and exits with a non-zero value. If you
+exception prints LIST to C<STDERR> and exits with a non-zero value. If you
need to exit the process with a specific exit code, see L</exit>.
Equivalent examples:
exit 255; # last resort
The intent is to squeeze as much possible information about the likely cause
-into the limited space of the system exit code. However, as C<$!> is the value
+into the limited space of the system exit
+code. However, as C<$!> is the value
of C's C<errno>, which can be set by any system call, this means that the value
of the exit code used by C<die> can be non-predictable, so should not be relied
upon, other than to be non-zero.
Not really a function. Returns the value of the last command in the
sequence of commands indicated by BLOCK. When modified by the C<while> or
C<until> loop modifier, executes the BLOCK once before testing the loop
-condition. (On other statements the loop modifiers test the conditional
+condition. (On other statements the loop modifiers test the conditional
first.)
C<do BLOCK> does I<not> count as a loop, so the loop control statements
resulting confusion by Perl.
This function is now largely obsolete, mostly because it's very hard to
-convert a core file into an executable. That's why you should now invoke
+convert a core file into an executable. That's why you should now invoke
it as C<CORE::dump()>, if you don't want to be warned against a possible
typo.
=item each EXPR
-When called in list context, returns a 2-element list consisting of the key
-and value for the next element of a hash, or the index and value for the
-next element of an array, so that you can iterate over it. When called in
-scalar context, returns only the key (not the value) in a hash, or the index
-in an array.
+When called on a hash in list context, returns a 2-element list
+consisting of the key and value for the next element of a hash. In Perl
+5.12 and later only, it will also return the index and value for the next
+element of an array so that you can iterate over it; older Perls consider
+this a syntax error. When called in scalar context, returns only the key
+(not the value) in a hash, or the index in an array.
Hash entries are returned in an apparently random order. The actual random
order is subject to change in future versions of Perl, but it is
After C<each> has returned all entries from the hash or array, the next
call to C<each> returns the empty list in list context and C<undef> in
-scalar context. The next call following that one restarts iteration. Each
-hash or array has its own internal iterator, accessed by C<each>, C<keys>,
-and C<values>. The iterator is implicitly reset when C<each> has reached
-the end as just described; it can be explicitly reset by calling C<keys> or
-C<values> on the hash or array. If you add or delete a hash's elements
-while iterating over it, entries may be skipped or duplicated--so don't do
-that. Exception: It is always safe to delete the item most recently
-returned by C<each()>, so the following code works properly:
+scalar context; the next call following I<that> one restarts iteration.
+Each hash or array has its own internal iterator, accessed by C<each>,
+C<keys>, and C<values>. The iterator is implicitly reset when C<each> has
+reached the end as just described; it can be explicitly reset by calling
+C<keys> or C<values> on the hash or array. If you add or delete a hash's
+elements while iterating over it, entries may be skipped or duplicated--so
+don't do that. Exception: In the current implementation, it is always safe
+to delete the item most recently returned by C<each()>, so the following
+code works properly:
while (($key, $value) = each %hash) {
print $key, "\n";
while (($key,$value) = each $hashref) { ... }
+To avoid confusing would-be users of your code who are running earlier
+versions of Perl with mysterious syntax errors, put this sort of thing at
+the top of your file to signal that your code will work I<only> on Perls of
+a recent vintage:
+
+ use 5.012; # so keys/values/each work on arrays
+ use 5.014; # so keys/values/each work on scalars (experimental)
+
See also C<keys>, C<values>, and C<sort>.
=item eof FILEHANDLE
print "--------------\n";
}
print;
- last if eof(); # needed if we're reading from a terminal
+ last if eof(); # needed if we're reading from a terminal
}
Practical hint: you almost never need to use C<eof> in Perl, because the
were a little Perl program. The value of the expression (which is itself
determined within scalar context) is first parsed, and if there were no
errors, executed as a block within the lexical context of the current Perl
-program. This means, that in particular, any outer lexical variables are
+program. This means, that in particular, any outer lexical variables are
visible to it, and any package variable settings or subroutine and format
definitions remain afterwards.
If EXPR is omitted, evaluates C<$_>. This form is typically used to
delay parsing and subsequent execution of the text of EXPR until run time.
+If the C<unicode_eval> feature is enabled (which is the default under a
+C<use 5.16> or higher declaration), EXPR or C<$_> is treated as a string of
+characters, so C<use utf8> declarations have no effect, and source filters
+are forbidden. In the absence of the C<unicode_eval> feature, the string
+will sometimes be treated as characters and sometimes as bytes, depending
+on the internal encoding, and source filters activated within the C<eval>
+exhibit the erratic, but historical, behaviour of affecting some outer file
+scope that is still compiling. See also the L</evalbytes> keyword, which
+always treats its input as a byte stream and works properly with source
+filters, and the L<feature> pragma.
+
In the second form, the code within the BLOCK is parsed only once--at the
same time the code surrounding the C<eval> itself was parsed--and executed
within the context of the current Perl program. This form is typically
If there is a syntax error or runtime error, or a C<die> statement is
executed, C<eval> returns C<undef> in scalar context
-or an empty list--or, for syntax errors, a list containing a single
-undefined value--in list context, and C<$@> is set to the error
-message. The discrepancy in the return values in list context is
-considered a bug by some, and will probably be fixed in a future
-release. If there was no error, C<$@> is guaranteed to be the empty
-string. Beware that using C<eval> neither silences Perl from printing
+or an empty list in list context, and C<$@> is set to the error
+message. (Prior to 5.16, a bug caused C<undef> to be returned
+in list context for syntax errors, but not for runtime errors.)
+If there was no error, C<$@> is set to the empty string. A
+control flow operator like C<last> or C<goto> can bypass the setting of
+C<$@>. 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, or
turn off warnings inside the BLOCK or EXPR using S<C<no warnings 'all'>>.
If you want to trap errors when loading an XS module, some problems with
the binary interface (such as Perl version skew) may be fatal even with
-C<eval> unless C<$ENV{PERL_DL_NONLAZY}> is set. See L<perlrun>.
+C<eval> unless C<$ENV{PERL_DL_NONLAZY}> is set.
See L<perlrun>.
If the code to be executed doesn't vary, you may use the eval-BLOCK
form to trap run-time errors without incurring the penalty of
in case 6.
Before Perl 5.14, the assignment to C<$@> occurred before restoration
-of localised variables, which means that for your code to run on older
+of localized variables, which means that for your code to run on older
versions, a temporary is required if you want to mask some but not all
errors:
An C<eval ''> executed within the C<DB> package doesn't see the usual
surrounding lexical scope, but rather the scope of the first non-DB piece
-of code that called it. You don't normally need to worry about this unless
+of code that called it. You don't normally need to worry about this unless
you are writing a Perl debugger.
+=item evalbytes EXPR
+X<evalbytes>
+
+=item evalbytes
+
+This function is like L</eval> with a string argument, except it always
+parses its argument, or C<$_> if EXPR is omitted, as a string of bytes. A
+string containing characters whose ordinal value exceeds 255 results in an
+error. Source filters activated within the evaluated code apply to the
+code itself.
+
+This function is only available under the C<evalbytes> feature, a
+C<use v5.16> (or higher) declaration, or with a C<CORE::> prefix. See
+L<feature> for more information.
+
=item exec LIST
X<exec> X<execute>
defined C<END> routines first, but these C<END> routines may not
themselves abort the exit. Likewise any object destructors that need to
be called are called before the real exit. C<END> routines and destructors
-can change the exit status by modifying C<$?>. If this is a problem, you
+can change the exit status by modifying C<$?>. If this is a problem, you
can call C<POSIX:_exit($status)> to avoid END and destructor processing.
See L<perlmod> for details.
Returns I<e> (the natural logarithm base) to the power of EXPR.
If EXPR is omitted, gives C<exp($_)>.
+=item fc EXPR
+X<fc> X<foldcase> X<casefold> X<fold-case> X<case-fold>
+
+=item fc
+
+Returns the casefolded version of EXPR. This is the internal function
+implementing the C<\F> escape in double-quoted strings.
+
+Casefolding is the process of mapping strings to a form where case
+differences are erased; comparing two strings in their casefolded
+form is effectively a way of asking if two strings are equal,
+regardless of case.
+
+Roughly, if you ever found yourself writing this
+
+ lc($this) eq lc($that) # Wrong!
+ # or
+ uc($this) eq uc($that) # Also wrong!
+ # or
+ $this =~ /\Q$that/i # Right!
+
+Now you can write
+
+ fc($this) eq fc($that)
+
+And get the correct results.
+
+Perl only implements the full form of casefolding.
+For further information on casefolding, refer to
+the Unicode Standard, specifically sections 3.13 C<Default Case Operations>,
+4.2 C<Case-Normative>, and 5.18 C<Case Mappings>,
+available at L<http://www.unicode.org/versions/latest/>, as well as the
+Case Charts available at L<http://www.unicode.org/charts/case/>.
+
+If EXPR is omitted, uses C<$_>.
+
+This function behaves the same way under various pragma, such as in a locale,
+as L</lc> does.
+
+While the Unicode Standard defines two additional forms of casefolding,
+one for Turkic languages and one that never maps one character into multiple
+characters, these are not provided by the Perl core; However, the CPAN module
+C<Unicode::Casing> may be used to provide an implementation.
+
+This keyword is available only when the C<"fc"> feature is enabled,
+or when prefixed with C<CORE::>; See L<feature>. Alternately,
+include a C<use v5.16> or later to the current scope.
+
=item fcntl FILEHANDLE,FUNCTION,SCALAR
X<fcntl>
Portability issues: L<perlport/fcntl>.
+=item __FILE__
+X<__FILE__>
+
+A special token that returns the name of the file in which it occurs.
+
=item fileno FILEHANDLE
X<fileno>
You should reopen those to F</dev/null> if it's any issue.
On some platforms such as Windows, where the fork() system call is not available,
-Perl can be built to emulate fork() in the Perl interpreter. The emulation is designed to,
-at the level of the Perl program, be as compatible as possible with the "Unix" fork().
+Perl can be built to emulate fork() in the Perl interpreter.
+The emulation is designed, at the level of the Perl program,
+to be as compatible as possible with the "Unix" fork().
However it has limitations that have to be considered in code intended to be portable.
See L<perlfork> for more details.
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
+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
+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>.
X<getpriority> X<priority> X<nice>
Returns the current priority for a process, a process group, or a user.
-(See C<getpriority(2)>.) Will raise a fatal exception if used on a
+(See L<getpriority(2)>.) Will raise a fatal exception if used on a
machine that doesn't implement getpriority(2).
Portability issues: L<perlport/getpriority>.
$ip_address = inet_ntoa($packed_ip);
}
-Make sure <gethostbyname()> is called in SCALAR context and that
+Make sure C<gethostbyname()> is called in SCALAR context and that
its return value is checked for definedness.
+The C<getprotobynumber> function, even though it only takes one argument,
+has the precedence of a list operator, so beware:
+
+ getprotobynumber $number eq 'icmp' # WRONG
+ getprotobynumber($number eq 'icmp') # actually means this
+ getprotobynumber($number) eq 'icmp' # better this way
+
If you get tired of remembering which element of the return list
contains which return value, by-name interfaces are provided
in standard modules: C<File::stat>, C<Net::hostent>, C<Net::netent>,
Queries the option named OPTNAME associated with SOCKET at a given LEVEL.
Options may exist at multiple protocol levels depending on the socket
type, but at least the uppermost socket level SOL_SOCKET (defined in the
-C<Socket> module) will exist. To query options at another level the
+C<Socket> module) will exist. To query options at another level the
protocol number of the appropriate protocol controlling the option
-should be supplied. For example, to indicate that an option is to be
+should be supplied. For example, to indicate that an option is to be
interpreted by the TCP protocol, LEVEL should be set to the protocol
number of TCP, which you can get using C<getprotobyname>.
The function returns a packed string representing the requested socket
option, or C<undef> on error, with the reason for the error placed in
-C<$!>. Just what is in the packed string depends on LEVEL and OPTNAME;
+C<$!>. Just what is in the packed string depends on LEVEL and OPTNAME;
consult getsockopt(2) for details. A common case is that the option is an
integer, in which case the result is a packed integer, which you can decode
using C<unpack> with the C<i> (or C<I>) format.
=item given BLOCK
-C<given> is analogous to the C<switch> keyword in other languages. C<given>
+C<given> is analogous to the C<switch>
+keyword in other languages. C<given>
and C<when> are used in Perl to implement C<switch>/C<case> like statements.
Only available after Perl 5.10. For example:
}
}
-See L<perlsyn/"Switch statements"> for detailed information.
+See L<perlsyn/"Switch Statements"> for detailed information.
=item glob EXPR
X<glob> X<wildcard> X<filename, expansion> X<expand>
=item glob
In list context, returns a (possibly empty) list of filename expansions on
-the value of EXPR such as the standard Unix shell F</bin/csh> would do. In
+the value of EXPR such as the standard Unix shell F</bin/csh> would do. In
scalar context, glob iterates through such filename expansions, returning
-undef when the list is exhausted. This is the internal function
-implementing the C<< <*.c> >> operator, but you can use it directly. If
+undef when the list is exhausted. This is the internal function
+implementing the C<< <*.c> >> operator, but you can use it directly. If
EXPR is omitted, C<$_> is used. The C<< <*.c> >> operator is discussed in
more detail in L<perlop/"I/O Operators">.
each segment as separate pattern. As such, C<glob("*.c *.h")>
matches all files with a F<.c> or F<.h> extension. The expression
C<glob(".* *")> matches all files in the current working directory.
+If you want to glob filenames that might contain whitespace, you'll
+have to use extra quotes around the spacey filename to protect it.
+For example, to glob filenames that have an C<e> followed by a space
+followed by an C<f>, use either of:
+
+ @spacies = <"*e f*">;
+ @spacies = glob '"*e f*"';
+ @spacies = glob q("*e f*");
+
+If you had to get a variable through, you could do this:
+
+ @spacies = glob "'*${var}e f*'";
+ @spacies = glob qq("*${var}e f*");
If non-empty braces are the only wildcard characters used in the
C<glob>, no filenames are matched, but potentially many strings
=item goto &NAME
The C<goto-LABEL> form finds the statement labeled with LABEL and
-resumes execution there. It can't be used to get out of a block or
+resumes execution there. It can't be used to get out of a block or
subroutine given to C<sort>. It can be used to go almost anywhere
else within the dynamic scope, including out of subroutines, but it's
usually better to use some other construct such as C<last> or C<die>.
goto ("FOO", "BAR", "GLARCH")[$i];
As shown in this example, C<goto-EXPR> is exempt from the "looks like a
-function" rule. A pair of parentheses following it does not (necessarily)
-delimit its argument. C<goto("NE")."XT"> is equivalent to C<goto NEXT>.
+function" rule. A pair of parentheses following it does not (necessarily)
+delimit its argument. C<goto("NE")."XT"> is equivalent to C<goto NEXT>.
Use of C<goto-LABEL> or C<goto-EXPR> to jump into a construct is
deprecated and will issue a warning. Even then, it may not be used to
Hex strings may only represent integers. Strings that would cause
integer overflow trigger a warning. Leading whitespace is not stripped,
-unlike oct(). To present something as hex, look into L</printf>,
+unlike oct(). To present something as hex, look into L</printf>,
L</sprintf>, and L</unpack>.
=item import LIST
or after POSITION. If POSITION is omitted, starts searching from the
beginning of the string. POSITION before the beginning of the string
or after its end is treated as if it were the beginning or the end,
-respectively. POSITION and the return value are based at C<0> (or whatever
-you've set the C<$[> variable to--but don't do that). If the substring
-is not found, C<index> returns one less than the base, ordinarily C<-1>.
+respectively. POSITION and the return value are based at zero.
+If the substring is not found, C<index> returns -1.
=item int EXPR
X<int> X<integer> X<truncate> X<trunc> X<floor>
=item keys EXPR
-Returns a list consisting of all the keys of the named hash, or the indices
-of an array. (In scalar context, returns the number of keys or indices.)
+Called in list context, returns a list consisting of all the keys of the
+named hash, or in Perl 5.12 or later only, the indices of an array. Perl
+releases prior to 5.12 will produce a syntax error if you try to use an
+array argument. In scalar context, returns the number of keys or indices.
The keys of a hash are returned in an apparently random order. The actual
random order is subject to change in future versions of Perl, but it
%hash> if you want to free the storage while C<%hash> is still in scope.
You can't shrink the number of buckets allocated for the hash using
C<keys> in this way (but you needn't worry about doing this by accident,
-as trying has no effect). C<keys @array> in an lvalue context is a syntax
+as trying has no effect). C<keys @array> in an lvalue context is a syntax
error.
Starting with Perl 5.14, C<keys> can take a scalar EXPR, which must contain
for (keys $hashref) { ... }
for (keys $obj->get_arrayref) { ... }
+To avoid confusing would-be users of your code who are running earlier
+versions of Perl with mysterious syntax errors, put this sort of thing at
+the top of your file to signal that your code will work I<only> on Perls of
+a recent vintage:
+
+ use 5.012; # so keys/values/each work on arrays
+ use 5.014; # so keys/values/each work on scalars (experimental)
+
See also C<each>, C<values>, and C<sort>.
=item kill SIGNAL, LIST
+
+=item kill SIGNAL
X<kill> X<signal>
Sends a signal to a list of processes. Returns the number of
L<perlport> for notes on the portability of this construct.
Unlike in the shell, if SIGNAL is negative, it kills process groups instead
-of processes. That means you usually want to use positive not negative signals.
+of processes. That means you usually
+want to use positive not negative signals.
You may also use a signal name in quotes.
The behavior of kill when a I<PROCESS> number is zero or negative depends on
See L<perlfork> for more details.
+If there is no I<LIST> of processes, no signal is sent, and the return
+value is 0. This form is sometimes used, however, because it causes
+tainting checks to be run. But see
+L<perlsec/Laundering and Detecting Tainted Data>.
+
Portability issues: L<perlport/kill>.
=item last LABEL
=back
-=item Otherwise, If EXPR has the UTF8 flag set
+=item Otherwise, if C<use locale> (but not C<use locale ':not_characters'>) is in effect:
-If the current package has a subroutine named C<ToLower>, it will be used to
-change the case
-(See L<perlunicode/"User-Defined Case Mappings (for serious hackers only)">.)
-Otherwise Unicode semantics are used for the case change.
+Respects current LC_CTYPE locale for code points < 256; and uses Unicode
+semantics for the remaining code points (this last can only happen if
+the UTF8 flag is also set). See L<perllocale>.
-=item Otherwise, if C<use locale> is in effect
+A deficiency in this is that case changes that cross the 255/256
+boundary are not well-defined. For example, the lower case of LATIN CAPITAL
+LETTER SHARP S (U+1E9E) in Unicode semantics is U+00DF (on ASCII
+platforms). But under C<use locale>, the lower case of U+1E9E is
+itself, because 0xDF may not be LATIN SMALL LETTER SHARP S in the
+current locale, and Perl has no way of knowing if that character even
+exists in the locale, much less what code point it is. Perl returns
+the input character unchanged, for all instances (and there aren't
+many) where the 255/256 boundary would otherwise be crossed.
-Respects current LC_CTYPE locale. See L<perllocale>.
+=item Otherwise, If EXPR has the UTF8 flag set:
-=item Otherwise, if C<use feature 'unicode_strings'> is in effect:
+Unicode semantics are used for the case change.
-Unicode semantics are used for the case change. Any subroutine named
-C<ToLower> will be ignored.
+=item Otherwise, if C<use feature 'unicode_strings'> or C<use locale ':not_characters'>) is in effect:
+
+Unicode semantics are used for the case change.
=item Otherwise:
UTF-8 would take up, use C<length(Encode::encode_utf8(EXPR))> (you'll have
to C<use Encode> first). See L<Encode> and L<perlunicode>.
+=item __LINE__
+X<__LINE__>
+
+A special token that compiles to the current line number.
+
=item link OLDFILE,NEWFILE
X<link>
print "$abbr[$mon] $mday";
# $mon=9, $mday=18 gives "Oct 18"
-C<$year> is the number of years since 1900, B<not> just the last two digits
-of the year. That is, C<$year> is C<123> in year 2023. The proper way
-to get a 4-digit year is simply:
+C<$year> contains the number of years since 1900. To get a 4-digit
+year write:
$year += 1900;
-Otherwise you create non-Y2K-compliant programs--and you wouldn't want
-to do that, would you?
-
To get the last two digits of the year (e.g., "01" in 2001) do:
$year = sprintf("%02d", $year % 100);
$now_string = localtime; # e.g., "Thu Oct 13 04:54:34 1994"
-This scalar value is B<not> locale-dependent but is a Perl builtin. For GMT
-instead of local time use the L</gmtime> builtin. See also the
+The format of this scalar value is B<not> locale-dependent
+but built into Perl. For GMT instead of local
+time use the L</gmtime> builtin. See also the
C<Time::Local> module (for converting seconds, minutes, hours, and such back to
the integer value returned by time()), and the L<POSIX> module's strftime(3)
and mktime(3) functions.
This function places an advisory lock on a shared variable or referenced
object contained in I<THING> until the lock goes out of scope.
+The value returned is the scalar itself, if the argument is a scalar, or a
+reference, if the argument is a hash, array or subroutine.
+
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. If you are not under C<use threads::shared> this does nothing.
See also L</exp> for the inverse operation.
-=item lstat EXPR
+=item lstat FILEHANDLE
X<lstat>
+=item lstat EXPR
+
+=item lstat DIRHANDLE
+
=item lstat
Does the same thing as the C<stat> function (including setting the
my @squares = map { $_ > 5 ? ($_ * $_) : () } @numbers;
shows that number of returned elements can differ from the number of
-input elements. To omit an element, return an empty list ().
+input elements. To omit an element, return an empty list ().
This could also be achieved by writing
my @squares = map { $_ * $_ } grep { $_ > 5 } @numbers;
Map always returns a list, which can be
assigned to a hash such that the elements
-become key/value pairs. See L<perldata> for more details.
+become key/value pairs.
See L<perldata> for more details.
%hash = map { get_a_key_for($_) => $_ } @array;
can't be seen from the outside, avoiding any potential side-effects.
C<{> starts both hash references and blocks, so C<map { ...> could be either
-the start of map BLOCK LIST or map EXPR, LIST. Because Perl doesn't look
+the start of map BLOCK LIST or map EXPR, LIST. Because Perl doesn't look
ahead for the closing C<}> it has to take a guess at which it's dealing with
-based on what it finds just after the C<{>. Usually it gets it right, but if it
+based on what it finds just after the
+C<{>. Usually it gets it right, but if it
doesn't it won't realize something is wrong until it gets to the C<}> and
-encounters the missing (or unexpected) comma. The syntax error will be
+encounters the missing (or unexpected) comma. The syntax error will be
reported close to the C<}>, but you'll need to change something near the C<{>
such as using a unary C<+> to give Perl some help:
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 cant usually use
+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>
You may (and usually should) use the three-argument form of open to specify
I/O layers (sometimes referred to as "disciplines") to apply to the handle
that affect how the input and output are processed (see L<open> and
-L<PerlIO> for more details). For example:
+L<PerlIO> for more details). For example:
open(my $fh, "<:encoding(UTF-8)", "filename")
|| die "can't open UTF-8 encoded filename: $!";
opens the UTF8-encoded file containing Unicode characters;
-see L<perluniintro>. Note that if layers are specified in the
+see L<perluniintro>. Note that if layers are specified in the
three-argument form, then default layers stored in ${^OPEN} (see L<perlvar>;
usually set by the B<open> pragma or the switch B<-CioD>) are ignored.
+Those layers will also be ignored if you specifying a colon with no name
+following it. In that case the default layer for the operating system
+(:raw on Unix, :crlf on Windows) is used.
Open returns nonzero on success, the undefined value otherwise. If
the C<open> involved a pipe, the return value happens to be the pid of
C<<< >> >>>, C<< < >>, C<< +> >>, C<<< +>> >>>, and C<< +< >>.
The mode you specify should match the mode of the original filehandle.
(Duping a filehandle does not take into account any existing contents
-of IO buffers.) If you use the three-argument form, then you can pass either a
+of IO buffers.) If you use the three-argument
+form, then you can pass either a
number, the name of a filehandle, or the normal "reference to a glob".
Here is a script that saves, redirects, and restores C<STDOUT> and
will have exactly the opposite restrictions.
-If you want a "real" C C<open> (see C<open(2)> on your system), then you
+If you want a "real" C C<open> (see L<open(2)> on your system), then you
should use the C<sysopen> function, which involves no such magic (but may
use subtly different filemodes than Perl open(), which is mapped to C
fopen()). This is another way to protect your filenames from
=item ord
-Returns the numeric (the native 8-bit encoding, like ASCII or EBCDIC,
-or Unicode) value of the first character of EXPR.
+Returns the numeric value of the first character of EXPR.
If EXPR is an empty string, returns 0. If EXPR is omitted, uses C<$_>.
(Note I<character>, not byte.)
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
+evolving. TYPE is currently bound to the use of the 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>.
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 (ascending bit order inside each byte,
+ like vec()).
B A bit string (descending bit order inside each byte).
h A hex string (low nybble first).
H A hex string (high nybble first).
q A signed quad (64-bit) value.
Q An unsigned quad value.
- (Quads are available only if your system supports 64-bit
- integer values _and_ if Perl has been compiled to support those.
- Raises an exception otherwise.)
+ (Quads are available only if your system supports 64-bit
+ integer values _and_ if Perl has been compiled to support
+ those. Raises an exception otherwise.)
i A signed integer value.
I A unsigned integer value.
- (This 'integer' is _at_least_ 32 bits wide. Its exact
- size depends on what a local C compiler calls 'int'.)
+ (This 'integer' is _at_least_ 32 bits wide. Its exact
+ size depends on what a local C compiler calls 'int'.)
n An unsigned short (16-bit) in "network" (big-endian) order.
N An unsigned long (32-bit) in "network" (big-endian) order.
v An unsigned short (16-bit) in "VAX" (little-endian) order.
V An unsigned long (32-bit) in "VAX" (little-endian) order.
- j A Perl internal signed integer value (IV).
- J A Perl internal unsigned integer value (UV).
+ j A Perl internal signed integer value (IV).
+ J A Perl internal unsigned integer value (UV).
f A single-precision float in native format.
d A double-precision float in native format.
F A Perl internal floating-point value (NV) in native format
D A float of long-double precision in native format.
- (Long doubles are available only if your system supports long
- double values _and_ if Perl has been compiled to support those.
- Raises an exception otherwise.)
+ (Long doubles are available only if your system supports
+ long double values _and_ if Perl has been compiled to
+ support those. Raises an exception 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 a character in character mode
- and UTF-8 (or UTF-EBCDIC in EBCDIC platforms) in byte mode.
+ U A Unicode character number. Encodes to a character in char-
+ acter mode and UTF-8 (or UTF-EBCDIC in EBCDIC platforms) in
+ byte mode.
- w A BER compressed integer (not an ASN.1 BER, see perlpacktut for
- details). Its bytes represent an unsigned integer in base 128,
- most significant digit first, with as few digits as possible. Bit
- eight (the high bit) is set on each byte except the last.
+ w A BER compressed integer (not an ASN.1 BER, see perlpacktut
+ for details). Its bytes represent an unsigned integer in
+ base 128, most significant digit first, with as few digits
+ as possible. Bit eight (the high bit) is set on each byte
+ except the last.
x A null byte (a.k.a ASCII NUL, "\000", chr(0))
X Back up a byte.
@ Null-fill or truncate to absolute position, counted from the
start of the innermost ()-group.
- . Null-fill or truncate to absolute position specified by the value.
+ . Null-fill or truncate to absolute position specified by
+ the value.
( Start of a ()-group.
One or more modifiers below may optionally follow certain letters in the
nNvV Treat integers as signed instead of unsigned.
@. Specify position as byte offset in the internal
- representation of the packed string. Efficient but
- dangerous.
+ representation of the packed string. Efficient
+ but dangerous.
> sSiIlLqQ Force big-endian byte-order on the type.
jJfFdDpP (The "big end" touches the construct.)
in C<pack("C[80]", @arr)>. The repeat count gobbles that many values from
the LIST when used with all format types other than C<a>, C<A>, C<Z>, C<b>,
C<B>, C<h>, C<H>, C<@>, C<.>, C<x>, C<X>, and C<P>, where it means
-something else, dscribed below. Supplying a C<*> for the repeat count
+something else, described below. Supplying a C<*> for the repeat count
instead of a number means to use however many items are left, except for:
=over
=back
The repeat count for C<u> is interpreted as the maximal number of bytes
-to encode per line of output, with 0, 1 and 2 replaced by 45. The repeat
+to encode per line of output, with 0, 1 and 2 replaced by 45. The repeat
count should not be more than 65.
=item *
within the structure itself as separate fields.
For C<pack>, you write I<length-item>C</>I<sequence-item>, and the
-I<length-item> describes how the length value is packed. Formats likely
+I<length-item> describes how the length value is packed. Formats 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.
For C<pack>, I<sequence-item> may have a repeat count, in which case
the minimum of that and the number of available items is used as the argument
-for I<length-item>. If it has no repeat count or uses a '*', the number
+for I<length-item>. If it has no repeat count or uses a '*', the number
of available items is used.
For C<unpack>, an internal stack of integer arguments unpacked so far is
-used. You write C</>I<sequence-item> and the repeat count is obtained by
-popping off the last element from the stack. The I<sequence-item> must not
+used. You write C</>I<sequence-item> and the repeat count is obtained by
+popping off the last element from the stack. The I<sequence-item> must not
have a repeat count.
If I<sequence-item> refers to a string type (C<"A">, C<"a">, or C<"Z">),
an explicit repeat count for pack, the packed string is adjusted to that
length. For example:
- unpack("W/a", "\004Gurusamy") gives ("Guru")
- unpack("a3/A A*", "007 Bond J ") gives (" Bond", "J")
- unpack("a3 x2 /A A*", "007: Bond, J.") gives ("Bond, J", ".")
+ This code: gives this result:
+
+ unpack("W/a", "\004Gurusamy") ("Guru")
+ unpack("a3/A A*", "007 Bond J ") (" Bond", "J")
+ unpack("a3 x2 /A A*", "007: Bond, J.") ("Bond, J", ".")
- pack("n/a* w/a","hello,","world") gives "\000\006hello,\005world"
- pack("a/W2", ord("a") .. ord("z")) gives "2ab"
+ pack("n/a* w/a","hello,","world") "\000\006hello,\005world"
+ pack("a/W2", ord("a") .. ord("z")) "2ab"
The I<length-item> is not returned explicitly from C<unpack>.
Pack and unpack can operate in two modes: character mode (C<C0> mode) where
the packed string is processed per character, and UTF-8 mode (C<U0> mode)
where the packed string is processed in its UTF-8-encoded Unicode form on
-a byte-by-byte basis. Character mode is the default unless the format string
-starts with C<U>. You can always switch mode mid-format with an explicit
+a byte-by-byte basis. Character mode is the default
+unless the format string starts with C<U>. You
+can always switch mode mid-format with an explicit
C<C0> or C<U0> in the format. This mode remains in effect until the next
mode change, or until the end of the C<()> group it (directly) applies to.
A C<()> group is a sub-TEMPLATE enclosed in parentheses. A group may
take a repeat count either as postfix, or for unpack(), also via the C</>
template character. Within each repetition of a group, positioning with
-C<@> starts over at 0. Therefore, the result of
+C<@> starts over at 0. Therefore, the result of
pack("@1A((@2A)@3A)", qw[X Y Z])
C<x> and C<X> accept the C<!> modifier to act as alignment commands: they
jump forward or back to the closest position aligned at a multiple of C<count>
-characters. For example, to pack() or unpack() a C structure like
+characters. For example, to pack() or unpack() a C structure like
struct {
char c; /* one signed, 8-bit character */
$foo = pack("W4",0x24b6,0x24b7,0x24b8,0x24b9);
# same thing with Unicode circled letters.
$foo = pack("U4",0x24b6,0x24b7,0x24b8,0x24b9);
- # same thing with Unicode circled letters. You don't get the UTF-8
- # bytes because the U at the start of the format caused a switch to
- # U0-mode, so the UTF-8 bytes get joined into characters
+ # same thing with Unicode circled letters. You don't get the
+ # UTF-8 bytes because the U at the start of the format caused
+ # a switch to U0-mode, so the UTF-8 bytes get joined into
+ # characters
$foo = pack("C0U4",0x24b6,0x24b7,0x24b8,0x24b9);
# foo eq "\xe2\x92\xb6\xe2\x92\xb7\xe2\x92\xb8\xe2\x92\xb9"
- # This is the UTF-8 encoding of the string in the previous example
+ # This is the UTF-8 encoding of the string in the
+ # previous example
$foo = pack("ccxxcc",65,66,67,68);
# foo eq "AB\0\0CD"
on all newly opened file descriptors whose C<fileno>s are I<higher> than
the current value of $^F (by default 2 for C<STDERR>). See L<perlvar/$^F>.
+=item __PACKAGE__
+X<__PACKAGE__>
+
+A special token that returns the name of the package in which it occurs.
+
=item pop ARRAY
X<pop> X<stack>
automatically. This aspect of C<pop> is considered highly experimental.
The exact behaviour may change in a future version of Perl.
+To avoid confusing would-be users of your code who are running earlier
+versions of Perl with mysterious syntax errors, put this sort of thing at
+the top of your file to signal that your code will work I<only> on Perls of
+a recent vintage:
+
+ use 5.014; # so push/pop/etc work on scalars (experimental)
+
=item pos SCALAR
X<pos> X<match, position>
Returns the offset of where the last C<m//g> search left off for the
variable in question (C<$_> is used when the variable is not
-specified). Note that 0 is a valid match offset. C<undef> indicates
+specified). Note that 0 is a valid match offset. C<undef> indicates
that the search position is reset (usually due to match failure, but
can also be because no match has yet been run on the scalar).
C<pos> directly accesses the location used by the regexp engine to
store the offset, so assigning to C<pos> will change that offset, and
so will also influence the C<\G> zero-width assertion in regular
-expressions. Both of these effects take place for the next match, so
+expressions. Both of these effects take place for the next match, so
you can't affect the position with C<pos> during the current match,
such as in C<(?{pos() = 5})> or C<s//pos() = 5/e>.
to the filehandle, thus introducing one level of indirection. (NOTE: If
FILEHANDLE is a variable and the next token is a term, it may be
misinterpreted as an operator unless you interpose a C<+> or put
-parentheses around the arguments.) If FILEHANDLE is omitted, prints to the
+parentheses around the arguments.) If FILEHANDLE is omitted, prints to the
last selected (see L</select>) output handle. If LIST is omitted, prints
C<$_> to the currently selected output handle. To use FILEHANDLE alone to
print the content of C<$_> to it, you must use a real filehandle like
Equivalent to C<print FILEHANDLE sprintf(FORMAT, LIST)>, except that C<$\>
(the output record separator) is not appended. The first argument of the
-list will be interpreted as the C<printf> format. See C<sprintf> for an
-explanation of the format argument. If you omit the LIST, C<$_> is used;
+list will be interpreted as the C<printf> format. See
+L<sprintf|/sprintf FORMAT, LIST> for an
+explanation of the format argument. If you omit the LIST, C<$_> is used;
to use FILEHANDLE without a LIST, you must use a real filehandle like
-C<FH>, not an indirect one like C<$fh>. If C<use locale> is in effect and
+C<FH>, not an indirect one like C<$fh>. If C<use locale> (including
+C<use locale ':not_characters'>) is in effect and
POSIX::setlocale() has been called, the character used for the decimal
separator in formatted floating-point numbers is affected by the LC_NUMERIC
locale setting. See L<perllocale> and L<POSIX>.
automatically. This aspect of C<push> is considered highly experimental.
The exact behaviour may change in a future version of Perl.
+To avoid confusing would-be users of your code who are running earlier
+versions of Perl with mysterious syntax errors, put this sort of thing at
+the top of your file to signal that your code will work I<only> on Perls of
+a recent vintage:
+
+ use 5.014; # so push/pop/etc work on scalars (experimental)
+
=item q/STRING/
=item qq/STRING/
quotemeta (and C<\Q> ... C<\E>) are useful when interpolating strings into
regular expressions, because by default an interpolated variable will be
-considered a mini-regular expression. For example:
+considered a mini-regular expression. For example:
my $sentence = 'The quick brown fox jumped over the lazy dog';
my $substring = 'quick.*?fox';
my $quoted_substring = quotemeta($substring);
$sentence =~ s{$quoted_substring}{big bad wolf};
-Will both leave the sentence as is. Normally, when accepting literal string
+Will both leave the sentence as is.
+Normally, when accepting literal string
input from the user, quotemeta() or C<\Q> must be used.
In Perl 5.14, all characters whose code points are above 127 are not
on it in security-sensitive situations.> As of this writing, a
number of third-party CPAN modules offer random number generators
intended by their authors to be cryptographically secure,
-including: L<Math::Random::Secure>, L<Math::Random::MT::Perl>, and
-L<Math::TrulyRandom>.
+including: L<Data::Entropy>, L<Crypt::Random>, L<Math::Random::Secure>,
+and L<Math::TrulyRandom>.
=item read FILEHANDLE,SCALAR,LENGTH,OFFSET
X<read> X<file, read>
bytes before the result of the read is appended.
The call is implemented in terms of either Perl's or your system's native
-fread(3) library function. To get a true read(2) system call, see C<sysread>.
+fread(3) library function. To get a true read(2) system call, see
+L<sysread|/sysread FILEHANDLE,SCALAR,LENGTH,OFFSET>.
Note the I<characters>: depending on the status of the filehandle,
either (8-bit) bytes or characters are read. By default, all
}
closedir $dh;
+To avoid confusing would-be users of your code who are running earlier
+versions of Perl with mysterious failures, put this sort of thing at the
+top of your file to signal that your code will work I<only> on Perls of a
+recent vintage:
+
+ use 5.012; # so readdir assigns to $_ in a lone while test
+
=item readline EXPR
=item readline
}
Note that you have can't handle C<readline> errors that way with the
-C<ARGV> filehandle. In that case, you have to open each element of
+C<ARGV> filehandle. In that case, you have to open each element of
C<@ARGV> yourself since C<eof> handles C<ARGV> differently.
foreach my $arg (@ARGV) {
=item ref
Returns a non-empty string if EXPR is a reference, the empty
-string otherwise. If EXPR
+string otherwise. If EXPR
is not specified, C<$_> will be used. The value returned depends on the
type of thing the reference is a reference to.
Builtin types include:
}
The return value C<LVALUE> indicates a reference to an lvalue that is not
-a variable. You get this from taking the reference of function calls like
-C<pos()> or C<substr()>. C<VSTRING> is returned if the reference points
+a variable. You get this from taking the reference of function calls like
+C<pos()> or C<substr()>. C<VSTRING> is returned if the reference points
to a L<version string|perldata/"Version Strings">.
The result C<Regexp> indicates that the argument is a regular expression
Now that you understand how C<require> looks for files with a
bareword argument, there is a little extra functionality going on behind
the scenes. Before C<require> looks for a "F<.pm>" extension, it will
-first look for a similar filename with a "F<.pmc>" extension. If this file
+first look for a similar filename with a "F<.pmc>" extension. If this file
is found, it will be loaded in place of any file ending in a "F<.pm>"
extension.
=item 2
-A reference to a subroutine. If there is no filehandle (previous item),
+A reference to a subroutine. If there is no filehandle (previous item),
then this subroutine is expected to generate one line of source code per
call, writing the line into C<$_> and returning 1, then finally at end of
file returning 0. If there is a filehandle, then the subroutine will be
=item 3
-Optional state for the subroutine. The state is passed in as C<$_[1]>. A
+Optional state for the subroutine. The state is passed in as C<$_[1]>. A
reference to the subroutine itself is passed in as C<$_[0]>.
=back
push @INC, Foo->new(...);
These hooks are also permitted to set the %INC entry
-corresponding to the files they have loaded. See L<perlvar/%INC>.
+corresponding to the files they have loaded.
See L<perlvar/%INC>.
For a yet-more-powerful import facility, see L</use> and L<perlmod>.
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
+may vary from one execution to the next (see L</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 void context.
FILEHANDLE without a LIST to print the contents of C<$_> to it, you must
use a real filehandle like C<FH>, not an indirect one like C<$fh>.
-This keyword is available only when the C<"say"> feature is enabled; see
+This keyword is available only when the C<"say"> feature
+is enabled, or when prefixed with C<CORE::>; see
L<feature>. Alternately, include a C<use v5.10> or later to the current
scope.
On some Unixes, select(2) may report a socket file descriptor as "ready for
reading" even when no data is available, and thus any subsequent C<read>
-would block. This can be avoided if you always use O_NONBLOCK on the
-socket. See select(2) and fcntl(2) for further details.
+would block. This can be avoided if you always use O_NONBLOCK on the
+socket. See select(2) and fcntl(2) for further details.
The standard C<IO::Select> module provides a user-friendlier interface
to C<select>, mostly because it does all the bit-mask work for you.
automatically. This aspect of C<shift> is considered highly experimental.
The exact behaviour may change in a future version of Perl.
+To avoid confusing would-be users of your code who are running earlier
+versions of Perl with mysterious syntax errors, put this sort of thing at
+the top of your file to signal that your code will work I<only> on Perls of
+a recent vintage:
+
+ use 5.014; # so push/pop/etc work on scalars (experimental)
+
See also C<unshift>, C<push>, and C<pop>. C<shift> and C<unshift> do the
same thing to the left end of an array that C<pop> and C<push> do to the
right end.
hold the data read. When writing, if STRING is too long, only SIZE
bytes are used; if STRING is too short, nulls are written to fill out
SIZE bytes. Return true if successful, false on error.
-shmread() taints the variable. See also L<perlipc/"SysV IPC">,
+shmread() taints the variable.
See also L<perlipc/"SysV IPC">,
C<IPC::SysV>, and the C<IPC::Shareable> module from CPAN.
Portability issues: L<perlport/shmread> and L<perlport/shmwrite>.
distribution) provides usleep(). You may also 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. See L<perlfaq8> for details.
+your system supports it.
See L<perlfaq8> for details.
See also the POSIX module's C<pause> function.
below). Note that in the latter case, it is usually highly counter-productive
to declare $a and $b as lexicals.
+If the subroutine is an XSUB, the elements to be compared are pushed on to
+the stack, the way arguments are usually passed to XSUBs. $a and $b are
+not set.
+
The values to be compared are always passed by reference and should not
be modified.
You also cannot exit out of the sort block or subroutine using any of the
loop control operators described in L<perlsyn> or with C<goto>.
-When C<use locale> is in effect, C<sort LIST> sorts LIST according to the
+When C<use locale> (but not C<use locale 'not_characters'>) is in
+effect, C<sort LIST> sorts LIST according to the
current collation locale. See L<perllocale>.
sort() returns aliases into the original list, much as a for loop's index
@articles = sort {$a cmp $b} @files;
# now case-insensitively
- @articles = sort {uc($a) cmp uc($b)} @files;
+ @articles = sort {fc($a) cmp fc($b)} @files;
# same thing in reversed order
@articles = sort {$b cmp $a} @files;
# sort using explicit subroutine name
sub byage {
- $age{$a} <=> $age{$b}; # presuming numeric
+ $age{$a} <=> $age{$b}; # presuming numeric
}
@sortedclass = sort byage @class;
my @new = sort {
($b =~ /=(\d+)/)[0] <=> ($a =~ /=(\d+)/)[0]
- ||
- uc($a) cmp uc($b)
+ ||
+ fc($a) cmp fc($b)
} @old;
# same thing, but much more efficiently;
my @nums = @caps = ();
for (@old) {
push @nums, ( /=(\d+)/ ? $1 : undef );
- push @caps, uc($_);
+ push @caps, fc($_);
}
my @new = @old[ sort {
- $nums[$b] <=> $nums[$a]
- ||
- $caps[$a] cmp $caps[$b]
- } 0..$#old
- ];
+ $nums[$b] <=> $nums[$a]
+ ||
+ $caps[$a] cmp $caps[$b]
+ } 0..$#old
+ ];
# same thing, but without any temps
@new = map { $_->[0] }
sort { $b->[1] <=> $a->[1]
- ||
- $a->[2] cmp $b->[2]
- } map { [$_, /=(\d+)/, uc($_)] } @old;
+ ||
+ $a->[2] cmp $b->[2]
+ } map { [$_, /=(\d+)/, fc($_)] } @old;
# using a prototype allows you to use any comparison subroutine
# as a sort subroutine (including other package's subroutines)
@new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;
Warning: syntactical care is required when sorting the list returned from
-a function. If you want to sort the list returned by the function call
+a function. If you want to sort the list returned by the function call
C<find_records(@key)>, you can use:
@contact = sort { $a cmp $b } find_records @key;
well-defined.
Because C<< <=> >> returns C<undef> when either operand is C<NaN>
-(not-a-number), and laso because C<sort> raises an exception unless the
-result of a comparison is defined, be careful when sorting with a
+(not-a-number), be careful when sorting with a
comparison function like C<< $a <=> $b >> any lists that might contain a
C<NaN>. The following example takes advantage that C<NaN != NaN> to
eliminate any C<NaN>s from the input list.
If LENGTH is omitted, removes everything from OFFSET onward.
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
+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 and $#a >= $i >> )
+The following equivalences hold (assuming C<< $#a >= $i >> )
push(@a,$x,$y) splice(@a,@a,0,$x,$y)
pop(@a) splice(@a,-1)
automatically. This aspect of C<splice> is considered highly experimental.
The exact behaviour may change in a future version of Perl.
+To avoid confusing would-be users of your code who are running earlier
+versions of Perl with mysterious syntax errors, put this sort of thing at
+the top of your file to signal that your code will work I<only> on Perls of
+a recent vintage:
+
+ use 5.014; # so push/pop/etc work on scalars (experimental)
+
=item split /PATTERN/,EXPR,LIMIT
X<split>
=item split
-Splits the string EXPR into a list of strings and returns that list. By
-default, empty leading fields are preserved, and empty trailing ones are
-deleted. (If all fields are empty, they are considered to be trailing.)
+Splits the string EXPR into a list of strings and returns the
+list in list context, or the size of the list in scalar context.
-In scalar context, returns the number of fields found.
+If only PATTERN is given, EXPR defaults to C<$_>.
-If EXPR is omitted, splits the C<$_> string. If PATTERN is also omitted,
-splits on whitespace (after skipping any leading whitespace). Anything
-matching PATTERN is taken to be a delimiter separating the fields. (Note
-that the delimiter may be longer than one character.)
+Anything in EXPR that matches PATTERN is taken to be a separator
+that separates the EXPR into substrings (called "I<fields>") that
+do B<not> include the separator. Note that a separator may be
+longer than one character or even have no characters at all (the
+empty string, which is a zero-width match).
+
+The PATTERN need not be constant; an expression may be used
+to specify a pattern that varies at runtime.
+
+If PATTERN matches the empty string, the EXPR is split at the match
+position (between characters). As an example, the following:
+
+ print join(':', split('b', 'abc')), "\n";
+
+uses the 'b' in 'abc' as a separator to produce the output 'a:c'.
+However, this:
+
+ print join(':', split('', 'abc')), "\n";
+
+uses empty string matches as separators to produce the output
+'a:b:c'; thus, the empty string may be used to split EXPR into a
+list of its component characters.
+
+As a special case for C<split>, the empty pattern given in
+L<match operator|perlop/"m/PATTERN/msixpodualgc"> syntax (C<//>) specifically matches the empty string, which is contrary to its usual
+interpretation as the last successful match.
+
+If PATTERN is C</^/>, then it is treated as if it used the
+L<multiline modifier|perlreref/OPERATORS> (C</^/m>), since it
+isn't much use otherwise.
+
+As another special case, C<split> emulates the default behavior of the
+command line tool B<awk> when the PATTERN is either omitted or a I<literal
+string> composed of a single space character (such as S<C<' '>> or
+S<C<"\x20">>, but not e.g. S<C</ />>). In this case, any leading
+whitespace in EXPR is removed before splitting occurs, and the PATTERN is
+instead treated as if it were C</\s+/>; in particular, this means that
+I<any> contiguous whitespace (not just a single space character) is used as
+a separator. However, this special treatment can be avoided by specifying
+the pattern S<C</ />> instead of the string S<C<" ">>, thereby allowing
+only a single space character to be a separator.
+
+If omitted, PATTERN defaults to a single space, S<C<" ">>, triggering
+the previously described I<awk> emulation.
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.
+of fields into which the EXPR may be split; in other words, LIMIT is
+one greater than the maximum number of times EXPR may be split. Thus,
+the LIMIT value C<1> means that EXPR may be split a maximum of zero
+times, producing a maximum of one field (namely, the entire value of
+EXPR). For instance:
-A pattern matching the empty string (not to be confused with
-an empty pattern C<//>, which is just one member of the set of patterns
-matching the epmty string), splits EXPR into individual
-characters. For example:
+ print join(':', split(//, 'abc', 1)), "\n";
- print join(':', split(/ */, 'hi there')), "\n";
+produces the output 'abc', and this:
-produces the output 'h:i:t:h:e:r:e'.
+ print join(':', split(//, 'abc', 2)), "\n";
-As a special case for C<split>, the empty pattern C<//> specifically
-matches the empty string; this is not be confused with the normal use
-of an empty pattern to mean the last successful match. So to split
-a string into individual characters, the following:
+produces the output 'a:bc', and each of these:
- print join(':', split(//, 'hi there')), "\n";
+ print join(':', split(//, 'abc', 3)), "\n";
+ print join(':', split(//, 'abc', 4)), "\n";
-produces the output 'h:i: :t:h:e:r:e'.
+produces the output 'a:b:c'.
-Empty leading fields are produced when there are positive-width matches at
-the beginning of the string; a zero-width match at the beginning of
-the string does not produce an empty field. For example:
+If LIMIT is negative, it is treated as if it were instead arbitrarily
+large; as many fields as possible are produced.
- print join(':', split(/(?=\w)/, 'hi there!'));
+If LIMIT is omitted (or, equivalently, zero), then it is usually
+treated as if it were instead negative but with the exception that
+trailing empty fields are stripped (empty leading fields are always
+preserved); if all fields are empty, then all fields are considered to
+be trailing (and are thus stripped in this case). Thus, the following:
-produces the output 'h:i :t:h:e:r:e!'. Empty trailing fields, on the other
-hand, are produced when there is a match at the end of the string (and
-when LIMIT is given and is not 0), regardless of the length of the match.
-For example:
+ print join(':', split(',', 'a,b,c,,,')), "\n";
- print join(':', split(//, 'hi there!', -1)), "\n";
- print join(':', split(/\W/, 'hi there!', -1)), "\n";
+produces the output 'a:b:c', but the following:
-produce the output 'h:i: :t:h:e:r:e:!:' and 'hi:there:', respectively,
-both with an empty trailing field.
+ print join(':', split(',', 'a,b,c,,,', -1)), "\n";
-The LIMIT parameter can be used to split a line partially
+produces the output 'a:b:c:::'.
- ($login, $passwd, $remainder) = split(/:/, $_, 3);
+In time-critical applications, it is worthwhile to avoid splitting
+into more fields than necessary. Thus, when assigning to a list,
+if LIMIT is omitted (or zero), then LIMIT is treated as though it
+were one larger than the number of variables in the list; for the
+following, LIMIT is implicitly 4:
-When assigning to a list, if LIMIT is omitted, or zero, Perl supplies
-a LIMIT one larger than the number of variables in the list, to avoid
-unnecessary work. For the list above LIMIT would have been 4 by
-default. In time critical applications it behooves you not to split
-into more fields than you really need.
+ ($login, $passwd, $remainder) = split(/:/);
-If the PATTERN contains parentheses, additional list elements are
-created from each matching substring in the delimiter.
+Note that splitting an EXPR that evaluates to the empty string always
+produces zero fields, regardless of the LIMIT specified.
- split(/([,-])/, "1-10,20", 3);
+An empty leading field is produced when there is a positive-width
+match at the beginning of EXPR. For instance:
-produces the list value
+ print join(':', split(/ /, ' abc')), "\n";
- (1, '-', 10, ',', 20)
+produces the output ':abc'. However, a zero-width match at the
+beginning of EXPR never produces an empty field, so that:
-If you had the entire header of a normal Unix email message in $header,
-you could split it up into fields and their values this way:
+ print join(':', split(//, ' abc'));
- $header =~ s/\n(?=\s)//g; # fix continuation lines
- %hdrs = (UNIX_FROM => split /^(\S*?):\s*/m, $header);
+produces the output S<' :a:b:c'> (rather than S<': :a:b:c'>).
-The pattern C</PATTERN/> may be replaced with an expression to specify
-patterns that vary at runtime. (To do runtime compilation only once,
-use C</$variable/o>.)
+An empty trailing field, on the other hand, is produced when there is a
+match at the end of EXPR, regardless of the length of the match
+(of course, unless a non-zero LIMIT is given explicitly, such fields are
+removed, as in the last example). Thus:
-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 initial null fields (empty string) as there are leading spaces.
-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 S<C<split(' ', $_)>> internally.
+ print join(':', split(//, ' abc', -1)), "\n";
-A PATTERN of C</^/> is treated as if it were C</^/m>, since it isn't
-much use otherwise.
+produces the output S<' :a:b:c:'>.
-Example:
+If the PATTERN contains
+L<capturing groups|perlretut/Grouping things and hierarchical matching>,
+then for each separator, an additional field is produced for each substring
+captured by a group (in the order in which the groups are specified,
+as per L<backreferences|perlretut/Backreferences>); if any group does not
+match, then it captures the C<undef> value instead of a substring. Also,
+note that any such additional field is produced whenever there is a
+separator (that is, whenever a split occurs), and such an additional field
+does B<not> count towards the LIMIT. Consider the following expressions
+evaluated in list context (each returned list is provided in the associated
+comment):
- open(PASSWD, '/etc/passwd');
- while (<PASSWD>) {
- chomp;
- ($login, $passwd, $uid, $gid,
- $gcos, $home, $shell) = split(/:/);
- #...
- }
+ split(/-|,/, "1-10,20", 3)
+ # ('1', '10', '20')
+
+ split(/(-|,)/, "1-10,20", 3)
+ # ('1', '-', '10', ',', '20')
+
+ split(/-|(,)/, "1-10,20", 3)
+ # ('1', undef, '10', ',', '20')
-As with regular pattern matching, any capturing parentheses that are not
-matched in a C<split()> will be set to C<undef> when returned:
+ split(/(-)|,/, "1-10,20", 3)
+ # ('1', '-', '10', undef, '20')
- @fields = split /(A)|B/, "1A2B3";
- # @fields is (1, 'A', 2, undef, 3)
+ split(/(-)|(,)/, "1-10,20", 3)
+ # ('1', '-', undef, '10', undef, ',', '20')
=item sprintf FORMAT, LIST
X<sprintf>
Returns a string formatted by the usual C<printf> conventions of the C
library function C<sprintf>. See below for more details
-and see
C<sprintf(3)> or C<printf(3)> on your system for an explanation of
+and see
L<sprintf(3)> or L<printf(3)> on your system for an explanation of
the general principles.
For example:
therefore unavailable from Perl.
Unlike C<printf>, C<sprintf> does not do what you probably mean when you
-pass it an array as your first argument. The array is given scalar context,
+pass it an array as your first argument.
+The array is given scalar context,
and instead of using the 0th element of the array as the format, Perl will
use the count of elements in the array as the format, which is almost never
useful.
%B like %b, but using an upper-case "B" with the # flag
%p a pointer (outputs the Perl value's address in hexadecimal)
%n special: *stores* the number of characters output so far
- into the next variable in the parameter list
+ into the next argument in the parameter list
Finally, for backward (and we do mean "backward") compatibility, Perl
permits these unnecessary but widely-supported conversions:
=item format parameter index
-An explicit format parameter index, such as C<2$>. By default sprintf
+An explicit format parameter index, such as C<2$>. By default sprintf
will format the next unused argument in the list, but this allows you
to take the arguments out of order:
=item vector flag
This flag tells Perl to interpret the supplied string as a vector of
-integers, one for each character in the string. Perl applies the format to
+integers, one for each character in the string. Perl applies the format to
each integer in turn, then joins the resulting strings with a separator (a
-dot C<.> by default). This can be useful for displaying ordinal values of
+dot C<.> by default). This can be useful for displaying ordinal values of
characters in arbitrary strings:
printf "%vd", "AB\x{100}"; # prints "65.66.256"
=item (minimum) width
Arguments are usually formatted to be only as wide as required to
-display the given value. You can override the width by putting
+display the given value. You can override the width by putting
a number here, or get the width from the next argument (with C<*>)
or from a specified argument (e.g., with C<*2$>):
printf '<%.1e>', 10; # prints "<1.0e+01>"
For "g" and "G", this specifies the maximum number of digits to show,
-including thoe prior to the decimal point and those after it; for
+including those prior to the decimal point and those after it; for
example:
# These examples are subject to system-specific variation.
=item size
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
+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,
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
+platform supports them. You can find out whether your Perl supports long
doubles via L<Config>:
use Config;
=item order of arguments
Normally, sprintf() takes the next unused argument as the value to
-format for each format specification. If the format specification
+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 they appear in the format
specification I<before> the value to format. Where an argument is
=back
-If C<use locale> is in effect and POSIX::setlocale() has been called,
+If C<use locale> (including C<use locale 'not_characters'>) is in effect
+and POSIX::setlocale() has been called,
the character used for the decimal separator in formatted floating-point
numbers is affected by the LC_NUMERIC locale. See L<perllocale>
and L<POSIX>.
Sets and returns 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. When called with a parameter, C<srand> uses that for the seed;
-otherwise it (semi-)randomly chooses a seed. In either case, starting with
-Perl 5.14, it returns the seed.
+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. When
+called with a parameter, C<srand> uses that for the seed; otherwise it
+(semi-)randomly chooses a seed. In either case, starting with Perl 5.14,
+it returns the seed. To signal that your code will work I<only> on Perls
+of a recent vintage:
+
+ use 5.014; # so srand returns the seed
If C<srand()> is not called explicitly, it is called implicitly without a
parameter at the first use of the C<rand> operator. However, this was not true
But there are a few situations in recent Perls where programs are likely to
want to call C<srand>. One is for generating predictable results generally for
testing or debugging. There, you use C<srand($seed)>, with the same C<$seed>
-each time. Another other case is where you 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. And still another case is that you may want to call C<srand()>
+each time. Another case is that you may want to call C<srand()>
after a C<fork()> to avoid child processes sharing the same seed value as the
parent (and consequently each other).
programs supply their own seed value (often C<time ^ $$> or C<time ^
($$ + ($$ << 15))>), but that isn't necessary any more.
-For cryptographic purposes, however, you need something much more random
-than the default seed. Checksumming the compressed output of one or more
-rapidly changing operating system status programs is the usual method. For
-example:
-
- srand (time ^ $$ ^ unpack "%L*", `ps axww | gzip -f`);
-
-If you're particularly concerned with this, search the CPAN for
-random number generator modules instead of rolling out your own.
-
Frequently called programs (like CGI scripts) that simply use
time ^ $$
can test a random subset each time, and should there be a failure, log the seed
used for that run so that it can later be used to reproduce the same results.
+B<C<rand()> is not cryptographically secure. You should not rely
+on it in security-sensitive situations.> As of this writing, a
+number of third-party CPAN modules offer random number generators
+intended by their authors to be cryptographically secure,
+including: L<Data::Entropy>, L<Crypt::Random>, L<Math::Random::Secure>,
+and L<Math::TrulyRandom>.
+
=item stat FILEHANDLE
X<stat> X<file, status> X<ctime>
(The epoch was at 00:00 January 1, 1970 GMT.)
-(*) Not all fields are supported on all filesystem types. Notably, the
+(*) Not all fields are supported on all filesystem types. Notably, 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.
S_IRWXO S_IROTH S_IWOTH S_IXOTH
# Setuid/Setgid/Stickiness/SaveText.
- # Note that the exact meaning of these is system dependent.
+ # Note that the exact meaning of these is system-dependent.
S_ISUID S_ISGID S_ISVTX S_ISTXT
- # File types. Not necessarily all are available on your system.
+ # File types. Not all are necessarily available on
+ # your system.
- S_IFREG S_IFDIR S_IFLNK S_IFBLK S_IFCHR S_IFIFO S_IFSOCK S_IFWHT S_ENFMT
+ S_IFREG S_IFDIR S_IFLNK S_IFBLK S_IFCHR
+ S_IFIFO S_IFSOCK S_IFWHT S_ENFMT
- # The following are compatibility aliases for S_IRUSR, S_IWUSR, S_IXUSR.
+ # The following are compatibility aliases for S_IRUSR,
+ # S_IWUSR, and S_IXUSR.
S_IREAD S_IWRITE S_IEXEC
and the C<S_IF*> functions are
- S_IMODE($mode) the part of $mode containing the permission bits
- and the setuid/setgid/sticky bits
+ S_IMODE($mode) the part of $mode containing the permission
+ bits and the setuid/setgid/sticky bits
- S_IFMT($mode) the part of $mode containing the file type
- which can be bit-anded with (for example) S_IFREG
- or with the following functions
+ S_IFMT($mode) the part of $mode containing the file type
+ which can be bit-anded with (for example)
+ S_IFREG or with the following functions
# The operators -f, -d, -l, -b, -c, -p, and -S.
=item state TYPE EXPR : ATTRS
-C<state> declares a lexically scoped variable, just like C<my> does.
+C<state> declares a lexically scoped variable, just like C<my>.
However, those variables will never be reinitialized, contrary to
lexical variables that are reinitialized each time their enclosing block
is entered.
+See L<perlsub/"Persistent Private Variables"> for details.
C<state> variables are enabled only when the C<use feature "state"> pragma
-is in effect. See L<feature>.
+is in effect, unless the keyword is written as C<CORE::state>.
+See also L<feature>.
=item study SCALAR
X<study>
frequencies in the string to be searched; you probably want to compare
run times with and without it to see which is faster. Those loops
that scan for many short constant strings (including the constant
-parts of more complex patterns) will benefit most. You may have only
-one C<study> active at a time: if you study a different scalar the first
-is "unstudied". (The way C<study> works is this: a linked list of every
+parts of more complex patterns) will benefit most.
+(The way C<study> works is this: a linked list of every
character in the string to be searched is made, so we know, for
example, where all the C<'k'> characters are. From each search string,
the rarest character is selected, based on some static frequency tables
references; see L<attributes> and L<Attribute::Handlers> for more
information about attributes.
+=item __SUB__
+X<__SUB__>
+
+A special token that returns the a reference to the current subroutine, or
+C<undef> outside of a subroutine.
+
+This token is only available under C<use v5.16> or the "current_sub"
+feature. See L<feature>.
+
=item substr EXPR,OFFSET,LENGTH,REPLACEMENT
X<substr> X<substring> X<mid> X<left> X<right>
=item substr EXPR,OFFSET
Extracts a substring out of EXPR and returns it. First character is at
-offset C<0> (or whatever you've set C<$[> to (but B<<don't do that>)).
-If OFFSET is negative (or more precisely, less than C<$[>), starts
+offset zero. If OFFSET is negative, starts
that far back from the end of the string. If LENGTH is omitted, returns
everything through the end of the string. If LENGTH is negative, leaves that
many characters off the end of the string.
$_ = 'pq'; print $x,"\n"; # prints 5pq9
}
-Prior to Perl version 5.9.1, the result of using an lvalue multiple times was
+With negative offsets, it remembers its position from the end of the string
+when the target string is modified:
+
+ $x = '1234';
+ for (substr($x, -3, 2)) {
+ $_ = 'a'; print $x,"\n"; # prints 1a4, as above
+ $x = 'abcdefg';
+ print $_,"\n"; # prints f
+ }
+
+Prior to Perl version 5.10, the result of using an lvalue multiple times was
+unspecified. Prior to 5.16, the result with negative offsets was
unspecified.
=item symlink OLDFILE,NEWFILE
Opens the file whose filename is given by FILENAME, and associates it with
FILEHANDLE. If FILEHANDLE is an expression, its value is used as the real
-filehandle wanted; an undefined scalar will be suitably autovivified. This
+filehandle wanted; an undefined scalar will be suitably autovivified. This
function calls the underlying operating system's I<open>(2) function with the
parameters FILENAME, MODE, and PERMS.
Note that C<sysopen> depends on the fdopen() C library function.
On many Unix systems, fdopen() is known to fail when file descriptors
-exceed a certain value, typically 255. If you need more file
+exceed a certain value, typically 255. If you need more file
descriptors than that, consider rebuilding Perl to use the C<sfio>
library, or perhaps using the POSIX::open() function.
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
+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 or an error of the wait(2) system
See L<perlop/"`STRING`"> and L</exec> for details.
Since C<system> does a C<fork> and C<wait> it may affect a C<SIGCHLD>
-handler. See L<perlipc> for details.
+handler.
See L<perlipc> for details.
Portability issues: L<perlport/system>.
Returns the number of non-leap seconds since whatever time the system
considers to be the epoch, suitable for feeding to C<gmtime> and
-C<localtime>. On most systems the epoch is 00:00:00 UTC, January 1, 1970;
+C<localtime>. On most systems the epoch is 00:00:00 UTC, January 1, 1970;
a prominent exception being Mac OS Classic which uses 00:00:00, January 1,
1904 in the current local time zone for its epoch.
=item unlink
-Deletes a list of files. On success, it returns the number of files
-it successfully deleted. On failure, it returns false and sets C<$!>
+Deletes a list of files. On success, it returns the number of files
+it successfully deleted. On failure, it returns false and sets C<$!>
(errno):
my $unlinked = unlink 'a', 'b', 'c';
}
Note: C<unlink> will not attempt to delete directories unless you are
-superuser and the B<-U> flag is supplied to Perl. Even if these
+superuser and the B<-U> flag is supplied to Perl. Even if these
conditions are met, be warned that unlinking a directory can inflict
damage on your filesystem. Finally, using C<unlink> on directories is
not supported on many operating systems. Use C<rmdir> instead.
See L</pack> for more examples and notes.
-=item untie VARIABLE
-X<untie>
-
-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
X<unshift>
automatically. This aspect of C<unshift> is considered highly
experimental. The exact behaviour may change in a future version of Perl.
+To avoid confusing would-be users of your code who are running earlier
+versions of Perl with mysterious syntax errors, put this sort of thing at
+the top of your file to signal that your code will work I<only> on Perls of
+a recent vintage:
+
+ use 5.014; # so push/pop/etc work on scalars (experimental)
+
+=item untie VARIABLE
+X<untie>
+
+Breaks the binding between a variable and a package.
+(See L<tie|/tie VARIABLE,CLASSNAME,LIST>.)
+Has no effect if the variable is not tied.
+
=item use Module VERSION LIST
X<use> X<module> X<import>
C<use>ing library modules that won't work with older versions of Perl.
(We try not to do this more than we have to.)
-Also, if the specified Perl version is greater than or equal to 5.9.5,
-C<use VERSION> will also load the C<feature> pragma and enable all
-features available in the requested version. See L<feature>.
+C<use VERSION> also enables all features available in the requested
+version as defined by the C<feature> pragma, disabling any features
+not in the current version's feature bundle. See L<feature>.
Similarly, if the specified Perl version is greater than or equal to
-5.11.0, strictures are enabled lexically as with C<use strict> (except
-that the F<strict.pm> file is not actually loaded).
+5.11.0, strictures are enabled lexically as
+with C<use strict>. Any explicit use of
+C<use strict> or C<no strict> overrides C<use VERSION>, even if it comes
+before it. In both cases, the F<feature.pm> and F<strict.pm> files are
+not actually loaded.
The C<BEGIN> forces the C<require> and C<import> to happen at compile time. The
C<require> makes sure the module is loaded into memory if it hasn't been
Since Perl 5.7.2, if the first two elements of the list are C<undef>,
the utime(2) syscall from your C library is called with a null second
-argument. On most systems, this will set the file's access and
+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) and will work even on files you don't own provided you have write
permission:
=item values EXPR
-Returns a list consisting of all the values of the named hash, or the values
-of an array. (In scalar context, returns the number of values.)
+In list context, returns a list consisting of all the values of the named
+hash. In Perl 5.12 or later only, will also return a list of the values of
+an array; prior to that release, attempting to use an array argument will
+produce a syntax error. In scalar context, returns the number of values.
-The values are returned in an apparently random order. The actual
-random order is subject to change in future versions of Perl, but it
-is guaranteed to be the same order as either the C<keys> or C<each>
-function would produce on the same (unmodified) hash. Since Perl
-5.8.1 the ordering is different even between different runs of Perl
-
for security reasons (see L<perlsec/"Algorithmic Complexity Attacks">).
+When called on a hash, the values are returned in an apparently random
+order. The actual random order is subject to change in future versions of
+Perl, but it is guaranteed to be the same order as either the C<keys> or
+C<each> function would produce on the same (unmodified) hash. Since Perl
+5.8.1 the ordering is different even between different runs of Perl for
+security reasons (see L<perlsec/"Algorithmic Complexity Attacks">).
As a side effect, calling values() resets the HASH or ARRAY's internal
-iterator;
-see L</each>. (In particular, calling values() in void context resets
-the iterator with no other overhead. Apart from resetting the iterator,
-C<values @array> in list context is the same as plain C<@array>.
-We recommend that you use void context C<keys @array> for this, but reasoned
-that it taking C<values @array> out would require more documentation than
-leaving it in.)
+iterator, see L</each>. (In particular, calling values() in void context
+resets the iterator with no other overhead. Apart from resetting the
+iterator, C<values @array> in list context is the same as plain C<@array>.
+(We recommend that you use void context C<keys @array> for this, but
+reasoned that taking C<values @array> out would require more
+documentation than leaving it in.)
Note that the values are not copied, which means modifying them will
modify the contents of the hash:
for (values $hashref) { ... }
for (values $obj->get_arrayref) { ... }
+To avoid confusing would-be users of your code who are running earlier
+versions of Perl with mysterious syntax errors, put this sort of thing at
+the top of your file to signal that your code will work I<only> on Perls of
+a recent vintage:
+
+ use 5.012; # so keys/values/each work on arrays
+ use 5.014; # so keys/values/each work on scalars (experimental)
+
See also C<keys>, C<each>, and C<sort>.
=item vec EXPR,OFFSET,BITS
being automatically reaped, as described in L<perlipc>.
If you use wait in your handler for $SIG{CHLD} it may accidentally for the
-child created by qx() or system(). See L<perlipc> for details.
+child created by qx() or system().
See L<perlipc> for details.
Portability issues: L<perlport/wait>.
=item when BLOCK
-C<when> is analogous to the C<case> keyword in other languages. Used with a
+C<when> is analogous to the C<case>
+keyword in other languages. Used with a
C<foreach> loop or the experimental C<given> block, C<when> can be used in
Perl to implement C<switch>/C<case> like statements. Available as a
statement after Perl 5.10 and as a statement modifier after 5.14.
}
}
-See L<perlsyn/"Switch statements"> for detailed information.
+See L<perlsyn/"Switch Statements"> for detailed information.
=item write FILEHANDLE
X<write>
room on the current page for the formatted record, the page is advanced by
writing a form feed, a special top-of-page format is used to format the new
page header before the record is written. By default, the top-of-page
-format is the name of the filehandle with "_TOP" appended. This would be a
+format is the name of the filehandle with "_TOP" appended. This would be a
problem with autovivified filehandles, but it may be dynamically set to the
format of your choice by assigning the name to the C<$^> variable while
that filehandle is selected. The number of lines remaining on the current
=back
+=head2 Non-function Keywords by Cross-reference
+
+=head3 perldata
+
+=over
+
+=item __DATA__
+
+=item __END__
+
+These keywords are documented in L<perldata>.
+
+=back
+
+=head3 perlmod
+
+=over
+
+=item BEGIN
+
+=item CHECK
+
+=item DESTROY
+
+=item END
+
+=item INIT
+
+=item UNITCHECK
+
+These keywords are documented in L<perlmod>.
+
+=back
+
+=head3 perlop
+
+=over
+
+=item and
+
+=item cmp
+
+=item eq
+
+=item ge
+
+=item gt
+
+=item if
+
+=item le
+
+=item lt
+
+=item ne
+
+=item not
+
+=item or
+
+=item x
+
+=item xor
+
+These operators are documented in L<perlop>.
+
+=back
+
+=head3 perlsub
+
+=over
+
+=item AUTOLOAD
+
+These are documented in L<perlsub>.
+
+=back
+
+=head3 perlsyn
+
+=over
+
+=item else
+
+=item elseif
+
+=item elsif
+
+=item for
+
+=item foreach
+
+=item unless
+
+=item until
+
+=item while
+
+These flow-control keywords are documented in L<perlsyn>.
+
+=back
+
=cut
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