Here are Perl's functions (including things that look like
functions, like some keywords and named operators)
arranged by category. Some functions appear in more
-than one place.
+than one place. Any warnings, including those produced by
+keywords, are described in L<perldiag> and L<warnings>.
=over 4
L<C<fcntl>|/fcntl FILEHANDLE,FUNCTION,SCALAR>, L<C<glob>|/glob EXPR>,
L<C<ioctl>|/ioctl FILEHANDLE,FUNCTION,SCALAR>,
L<C<link>|/link OLDFILE,NEWFILE>, L<C<lstat>|/lstat FILEHANDLE>,
-L<C<mkdir>|/mkdir FILENAME,MASK>, L<C<open>|/open FILEHANDLE,EXPR>,
+L<C<mkdir>|/mkdir FILENAME,MODE>, L<C<open>|/open FILEHANDLE,EXPR>,
L<C<opendir>|/opendir DIRHANDLE,EXPR>, L<C<readlink>|/readlink EXPR>,
L<C<rename>|/rename OLDNAME,NEWNAME>, L<C<rmdir>|/rmdir FILENAME>,
L<C<select>|/select FILEHANDLE>, L<C<stat>|/stat FILEHANDLE>,
tests STDIN. Unless otherwise documented, it returns C<1> for true and
C<''> for false. If the file doesn't exist or can't be examined, it
returns L<C<undef>|/undef EXPR> and sets L<C<$!>|perlvar/$!> (errno).
+With the exception of the C<-l> test they all follow symbolic links
+because they use C<stat()> and not C<lstat()> (so dangling symlinks can't
+be examined and will therefore report failure).
+
Despite the funny names, precedence is the same as any other named unary
operator. The operator may be any of:
=for Pod::Functions create an object
This function tells the thingy referenced by REF that it is now an object
-in the CLASSNAME package. If CLASSNAME is omitted, the current package
+in the CLASSNAME package. If CLASSNAME is an empty string, it is
+interpreted as referring to the C<main> package.
+If CLASSNAME is omitted, the current package
is used. Because a L<C<bless>|/bless REF,CLASSNAME> 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
Consider always blessing objects in CLASSNAMEs that are mixed case.
Namespaces with all lowercase names are considered reserved for
Perl pragmas. 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.
+confusion, you may wish to avoid such package names as well.
+It is advised to avoid the class name C<0>, because much code erroneously
+uses the result of L<C<ref>|/ref EXPR> as a truth value.
See L<perlmod/"Perl Modules">.
true. Setting a hash element to the undefined value does not remove its
key, but deleting it does; see L<C<exists>|/exists EXPR>.
-In list context, returns the value or values deleted, or the last such
-element in scalar context. The return list's length always matches that of
+In list context, usually returns the value or values deleted, or the last such
+element in scalar context. The return list's length corresponds to that of
the argument list: deleting non-existent elements returns the undefined value
-in their corresponding positions.
+in their corresponding positions. When a
+L<keyE<sol>value hash slice|perldata/KeyE<sol>Value Hash Slices> is passed to
+C<delete>, the return value is a list of key/value pairs (two elements for each
+item deleted from the hash).
L<C<delete>|/delete EXPR> may also be used on arrays and array slices,
but its behavior is less straightforward. Although
=for Pod::Functions raise an exception or bail out
-L<C<die>|/die LIST> raises an exception. Inside an
-L<C<eval>|/eval EXPR> the error message is stuffed into
-L<C<$@>|perlvar/$@> and the L<C<eval>|/eval EXPR> is terminated with the
-undefined value. If the exception is outside of all enclosing
-L<C<eval>|/eval EXPR>s, then the uncaught 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<C<exit>|/exit EXPR>.
+L<C<die>|/die LIST> raises an exception. Inside an L<C<eval>|/eval EXPR>
+the exception is stuffed into L<C<$@>|perlvar/$@> and the L<C<eval>|/eval
+EXPR> is terminated with the undefined value. If the exception is
+outside of all enclosing L<C<eval>|/eval EXPR>s, then the uncaught
+exception is printed to C<STDERR> and perl exits with an exit code
+indicating failure. If you need to exit the process with a specific
+exit code, see L<C<exit>|/exit EXPR>.
Equivalent examples:
die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news';
chdir '/usr/spool/news' or die "Can't cd to spool: $!\n"
-If the last element of LIST does not end in a newline, the current
-script line number and input line number (if any) are also printed,
-and a newline is supplied. Note that the "input line number" (also
+Most of the time, C<die> is called with a string to use as the exception.
+You may either give a single non-reference operand to serve as the
+exception, or a list of two or more items, which will be stringified
+and concatenated to make the exception.
+
+If the string exception does not end in a newline, the current
+script line number and input line number (if any) and a newline
+are appended to it. Note that the "input line number" (also
known as "chunk") is subject to whatever notion of "line" happens to
be currently in effect, and is also available as the special variable
L<C<$.>|perlvar/$.>. See L<perlvar/"$/"> and L<perlvar/"$.">.
/etc/games is no good at canasta line 123.
/etc/games is no good, stopped at canasta line 123.
-If the output is empty and L<C<$@>|perlvar/$@> already contains a value
-(typically from a previous L<C<eval>|/eval EXPR>) that value is reused after
+If LIST was empty or made an empty string, and L<C<$@>|perlvar/$@>
+already contains an exception value (typically from a previous
+L<C<eval>|/eval EXPR>), then that value is reused after
appending C<"\t...propagated">. This is useful for propagating exceptions:
eval { ... };
die unless $@ =~ /Expected exception/;
-If the output is empty and L<C<$@>|perlvar/$@> contains an object
+If LIST was empty or made an empty string,
+and L<C<$@>|perlvar/$@> contains an object
reference that has a C<PROPAGATE> method, that method will be called
with additional file and line number parameters. The return value
replaces the value in L<C<$@>|perlvar/$@>; i.e., as if
C<< $@ = eval { $@->PROPAGATE(__FILE__, __LINE__) }; >> were called.
-If L<C<$@>|perlvar/$@> is empty, then the string C<"Died"> is used.
-
-If an uncaught exception results in interpreter exit, the exit code is
-determined from the values of L<C<$!>|perlvar/$!> and
-L<C<$?>|perlvar/$?> with this pseudocode:
-
- exit $! if $!; # errno
- exit $? >> 8 if $? >> 8; # child exit status
- exit 255; # last resort
-
-As with L<C<exit>|/exit EXPR>, L<C<$?>|perlvar/$?> is set prior to
-unwinding the call stack; any C<DESTROY> or C<END> handlers can then
-alter this value, and thus Perl's exit code.
-
-The intent is to squeeze as much possible information about the likely cause
-into the limited space of the system exit code. However, as
-L<C<$!>|perlvar/$!> is the value of C's C<errno>, which can be set by
-any system call, this means that the value of the exit code used by
-L<C<die>|/die LIST> can be non-predictable, so should not be relied
-upon, other than to be non-zero.
+If LIST was empty or made an empty string, and L<C<$@>|perlvar/$@>
+is also empty, then the string C<"Died"> is used.
You can also call L<C<die>|/die LIST> with a reference argument, and if
this is trapped within an L<C<eval>|/eval EXPR>, L<C<$@>|perlvar/$@>
contains that reference. This permits more elaborate exception handling
using objects that maintain arbitrary state about the exception. Such a
scheme is sometimes preferable to matching particular string values of
-L<C<$@>|perlvar/$@> with regular expressions. Because
-L<C<$@>|perlvar/$@> is a global variable and L<C<eval>|/eval EXPR> may
-be used within object implementations, be careful that analyzing the
-error object doesn't replace the reference in the global variable. It's
+L<C<$@>|perlvar/$@> with regular expressions.
+
+Because Perl stringifies uncaught exception messages before display,
+you'll probably want to overload stringification operations on
+exception objects. See L<overload> for details about that.
+The stringified message should be non-empty, and should end in a newline,
+in order to fit in with the treatment of string exceptions.
+Also, because an exception object reference cannot be stringified
+without destroying it, Perl doesn't attempt to append location or other
+information to a reference exception. If you want location information
+with a complex exception object, you'll have to arrange to put the
+location information into the object yourself.
+
+Because L<C<$@>|perlvar/$@> is a global variable, be careful that
+analyzing an exception caught by C<eval> doesn't replace the reference
+in the global variable. It's
easiest to make a local copy of the reference before any manipulations.
Here's an example:
}
}
-Because Perl stringifies uncaught exception messages before display,
-you'll probably want to overload stringification operations on
-exception objects. See L<overload> for details about that.
+If an uncaught exception results in interpreter exit, the exit code is
+determined from the values of L<C<$!>|perlvar/$!> and
+L<C<$?>|perlvar/$?> with this pseudocode:
+
+ exit $! if $!; # errno
+ exit $? >> 8 if $? >> 8; # child exit status
+ exit 255; # last resort
+
+As with L<C<exit>|/exit EXPR>, L<C<$?>|perlvar/$?> is set prior to
+unwinding the call stack; any C<DESTROY> or C<END> handlers can then
+alter this value, and thus Perl's exit code.
+
+The intent is to squeeze as much possible information about the likely cause
+into the limited space of the system exit code. However, as
+L<C<$!>|perlvar/$!> is the value of C's C<errno>, which can be set by
+any system call, this means that the value of the exit code used by
+L<C<die>|/die LIST> can be non-predictable, so should not be relied
+upon, other than to be non-zero.
You can arrange for a callback to be run just before the
L<C<die>|/die LIST> does its deed, by setting the
L<C<$SIG{__DIE__}>|perlvar/%SIG> hook. The associated handler is called
-with the error text and can change the error message, if it sees fit, by
+with the exception as an argument, and can change the exception,
+if it sees fit, by
calling L<C<die>|/die LIST> again. See L<perlvar/%SIG> for details on
setting L<C<%SIG>|perlvar/%SIG> entries, and L<C<eval>|/eval EXPR> for some
examples. Although this feature was to be run only right before your
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
-it as C<CORE::dump()> if you don't want to be warned against a possible
-typo.
+convert a core file into an executable. As of Perl 5.30, it must be invoked
+as C<CORE::dump()>.
Unlike most named operators, this has the same precedence as assignment.
It is also exempt from the looks-like-a-function rule, so
L<C<keys>|/keys HASH>, and L<C<values>|/values HASH>. The iterator is
implicitly reset when L<C<each>|/each HASH> has reached the end as just
described; it can be explicitly reset by calling L<C<keys>|/keys HASH>
-or L<C<values>|/values HASH> on the hash or array. If you add or delete
+or L<C<values>|/values HASH> on the hash or array, or by referencing
+the hash (but not array) in list context. If you add or delete
a hash's elements while iterating over it, the effect on the iterator is
unspecified; for example, entries may be skipped or duplicated--so don't
do that. Exception: It is always safe to delete the item most recently
Tied hashes may have a different ordering behaviour to perl's hash
implementation.
+The iterator used by C<each> is attached to the hash or array, and is
+shared between all iteration operations applied to the same hash or array.
+Thus all uses of C<each> on a single hash or array advance the same
+iterator location. All uses of C<each> are also subject to having the
+iterator reset by any use of C<keys> or C<values> on the same hash or
+array, or by the hash (but not array) being referenced in list context.
+This makes C<each>-based loops quite fragile: it is easy to arrive at
+such a loop with the iterator already part way through the object, or to
+accidentally clobber the iterator state during execution of the loop body.
+It's easy enough to explicitly reset the iterator before starting a loop,
+but there is no way to insulate the iterator state used by a loop from
+the iterator state used by anything else that might execute during the
+loop body. To avoid these problems, use a C<foreach> loop rather than
+C<while>-C<each>.
+
This prints out your environment like the L<printenv(1)> program,
but in a different order:
As of Perl 5.18 you can use a bare L<C<each>|/each HASH> in a C<while>
loop, which will set L<C<$_>|perlvar/$_> on every iteration.
+If either an C<each> expression or an explicit assignment of an C<each>
+expression to a scalar is used as a C<while>/C<for> condition, then
+the condition actually tests for definedness of the expression's value,
+not for its regular truth value.
while (each %ENV) {
print "$_=$ENV{$_}\n";
if (exists $ref->{"Some key"}) { }
print $ref; # prints HASH(0x80d3d5c)
-This surprising autovivification in what does not at first--or even
-second--glance appear to be an lvalue context may be fixed in a future
-release.
-
Use of a subroutine call, rather than a subroutine name, as an argument
to L<C<exists>|/exists EXPR> is an error.
they aren't, because a C<File::stat> object is different from
a C<User::pwent> object.
+Many of these functions are not safe in a multi-threaded environment
+where more than one thread can be using them. In particular, functions
+like C<getpwent()> iterate per-process and not per-thread, so if two
+threads are simultaneously iterating, neither will get all the records.
+
+Some systems have thread-safe versions of some of the functions, such as
+C<getpwnam_r()> instead of C<getpwnam()>. There, Perl automatically and
+invisibly substitutes the thread-safe version, without notice. This
+means that code that safely runs on some systems can fail on others that
+lack the thread-safe versions.
+
Portability issues: L<perlport/getpwnam> to L<perlport/endservent>.
=item getsockname SOCKET
L<C<bsd_glob>|File::Glob/C<bsd_glob>>, which does not treat whitespace
as a pattern separator.
+If a C<glob> expression is used as the condition of a C<while> or C<for>
+loop, then it will be implicitly assigned to C<$_>. If either a C<glob>
+expression or an explicit assignment of a C<glob> expression to a scalar
+is used as a C<while>/C<for> condition, then the condition actually
+tests for definedness of the expression's value, not for its regular
+truth value.
+
Portability issues: L<perlport/glob>.
=item gmtime EXPR
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
go into any construct that requires initialization, such as a
-subroutine or a C<foreach> loop. It also can't be used to go into a
+subroutine, a C<foreach> loop, or a C<given>
+block. In general, it may not be used to jump into the parameter
+of a binary or list operator, but it may be used to jump into the
+I<first> parameter of a binary operator. (The C<=>
+assignment operator's "first" operand is its right-hand
+operand.) It also can't be used to go into a
construct that is optimized away.
The C<goto &NAME> form is quite different from the other forms of
insertion and deletion of items.
As a side effect, calling L<C<keys>|/keys HASH> resets the internal
-iterator of the HASH or ARRAY (see L<C<each>|/each HASH>). In
+iterator of the HASH or ARRAY (see L<C<each>|/each HASH>) before
+yielding the keys. In
particular, calling L<C<keys>|/keys HASH> in void context resets the
iterator with no other overhead.
#...
}
-L<C<last>|/last LABEL> cannot be used to exit a block that returns a
-value such as C<eval {}>, C<sub {}>, or C<do {}>, and should not be used
-to exit a L<C<grep>|/grep BLOCK LIST> or L<C<map>|/map BLOCK LIST>
+L<C<last>|/last LABEL> cannot return a value from a block that typically
+returns a value, such as C<eval {}>, C<sub {}>, or C<do {}>. It will perform
+its flow control behavior, which precludes any return value. It should not be
+used to exit a L<C<grep>|/grep BLOCK LIST> or L<C<map>|/map BLOCK LIST>
operation.
Note that a block by itself is semantically identical to a loop
to get a list of anonymous hashes each with only one entry apiece.
-=item mkdir FILENAME,MASK
+=item mkdir FILENAME,MODE
X<mkdir> X<md> X<directory, create>
=item mkdir FILENAME
=for Pod::Functions create a directory
Creates the directory specified by FILENAME, with permissions
-specified by MASK (as modified by L<C<umask>|/umask EXPR>). If it
+specified by MODE (as modified by L<C<umask>|/umask EXPR>). If it
succeeds it returns true; otherwise it returns false and sets
L<C<$!>|perlvar/$!> (errno).
-MASK defaults to 0777 if omitted, and FILENAME defaults
+MODE defaults to 0777 if omitted, and FILENAME defaults
to L<C<$_>|perlvar/$_> if omitted.
-In general, it is better to create directories with a permissive MASK
+In general, it is better to create directories with a permissive MODE
and let the user modify that with their L<C<umask>|/umask EXPR> than it
is to supply
-a restrictive MASK and give the user no way to be more permissive.
+a restrictive MODE and give the user no way to be more permissive.
The exceptions to this rule are when the file or directory should be
kept private (mail files, for instance). The documentation for
-L<C<umask>|/umask EXPR> discusses the choice of MASK in more detail.
+L<C<umask>|/umask EXPR> discusses the choice of MODE in more detail.
Note that according to the POSIX 1003.1-1996 the FILENAME may have any
number of trailing slashes. Some operating and filesystems do not get
as of Perl 5.18.0, allows a label name to be computed at run time, being
otherwise identical to C<next LABEL>.
-L<C<next>|/next LABEL> cannot be used to exit a block which returns a
-value such as C<eval {}>, C<sub {}>, or C<do {}>, and should not be used
-to exit a L<C<grep>|/grep BLOCK LIST> or L<C<map>|/map BLOCK LIST>
+L<C<next>|/next LABEL> cannot return a value from a block that typically
+returns a value, such as C<eval {}>, C<sub {}>, or C<do {}>. It will perform
+its flow control behavior, which precludes any return value. It should not be
+used to exit a L<C<grep>|/grep BLOCK LIST> or L<C<map>|/map BLOCK LIST>
operation.
Note that a block by itself is semantically identical to a loop
As of Perl 5.12 you can use a bare L<C<readdir>|/readdir DIRHANDLE> in a
C<while> loop, which will set L<C<$_>|perlvar/$_> on every iteration.
+If either a C<readdir> expression or an explicit assignment of a
+C<readdir> expression to a scalar is used as a C<while>/C<for> condition,
+then the condition actually tests for definedness of the expression's
+value, not for its regular truth value.
opendir(my $dh, $some_dir) || die "Can't open $some_dir: $!";
while (readdir $dh) {
}
}
+Like the C<< <EXPR> >> operator, if a C<readline> expression is
+used as the condition of a C<while> or C<for> loop, then it will be
+implicitly assigned to C<$_>. If either a C<readline> expression or
+an explicit assignment of a C<readline> expression to a scalar is used
+as a C<while>/C<for> condition, then the condition actually tests for
+definedness of the expression's value, not for its regular truth value.
+
=item readlink EXPR
X<readlink>
This call is actually implemented in terms of the L<recvfrom(2)> system call.
See L<perlipc/"UDP: Message Passing"> for examples.
-Note the I<characters>: depending on the status of the socket, either
-(8-bit) bytes or characters are received. By default all sockets
-operate on bytes, but for example if the socket has been changed using
-L<C<binmode>|/binmode FILEHANDLE, LAYER> to operate with the
-C<:encoding(UTF-8)> I/O layer (see the L<open> pragma), the I/O will
-operate on UTF8-encoded Unicode
-characters, not bytes. Similarly for the C<:encoding> layer: in that
-case pretty much any characters can be read.
+Note that if the socket has been marked as C<:utf8>, C<recv> will
+throw an exception. The C<:encoding(...)> layer implicitly introduces
+the C<:utf8> layer. See L<C<binmode>|/binmode FILEHANDLE, LAYER>.
=item redo LABEL
X<redo>
print;
}
-L<C<redo>|/redo LABEL> cannot be used to retry a block that returns a
-value such as C<eval {}>, C<sub {}>, or C<do {}>, and should not be used
-to exit a L<C<grep>|/grep BLOCK LIST> or L<C<map>|/map BLOCK LIST>
+L<C<redo>|/redo LABEL> cannot return a value from a block that typically
+returns a value, such as C<eval {}>, C<sub {}>, or C<do {}>. It will perform
+its flow control behavior, which precludes any return value. It should not be
+used to exit a L<C<grep>|/grep BLOCK LIST> or L<C<map>|/map BLOCK LIST>
operation.
Note that a block by itself is semantically identical to a loop
=for Pod::Functions find out the type of thing being referenced
-Returns a non-empty string if EXPR is a reference, the empty
-string otherwise. If EXPR is not specified, L<C<$_>|perlvar/$_> will be
-used. The value returned depends on the type of thing the reference is
-a reference to.
-
-Builtin types include:
-
- SCALAR
- ARRAY
- HASH
- CODE
- REF
- GLOB
- LVALUE
- FORMAT
- IO
- VSTRING
- Regexp
-
-You can think of L<C<ref>|/ref EXPR> as a C<typeof> operator.
-
- if (ref($r) eq "HASH") {
- print "r is a reference to a hash.\n";
- }
- unless (ref($r)) {
- print "r is not a reference at all.\n";
- }
-
-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
-L<C<pos>|/pos SCALAR> or
-L<C<substr>|/substr EXPR,OFFSET,LENGTH,REPLACEMENT>. 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
-resulting from L<C<qrE<sol>E<sol>>|/qrE<sol>STRINGE<sol>>.
-
-If the referenced object has been blessed into a package, then that package
-name is returned instead. But don't use that, as it's now considered
-"bad practice". For one reason, an object could be using a class called
-C<Regexp> or C<IO>, or even C<HASH>. Also, L<C<ref>|/ref EXPR> doesn't
-take into account subclasses, like
-L<C<isa>|UNIVERSAL/C<< $obj->isa( TYPE ) >>> does.
-
-Instead, use L<C<blessed>|Scalar::Util/blessed> (in the L<Scalar::Util>
-module) for boolean checks, L<C<isa>|UNIVERSAL/C<< $obj->isa( TYPE ) >>>
-for specific class checks and L<C<reftype>|Scalar::Util/reftype> (also
-from L<Scalar::Util>) for type checks. (See L<perlobj> for details and
-a L<C<blessed>|Scalar::Util/blessed>/L<C<isa>|UNIVERSAL/C<< $obj->isa( TYPE ) >>>
-example.)
-
-See also L<perlref>.
+Examines the value of EXPR, expecting it to be a reference, and returns
+a string giving information about the reference and the type of referent.
+If EXPR is not specified, L<C<$_>|perlvar/$_> will be used.
+
+If the operand is not a reference, then the empty string will be returned.
+An empty string will only be returned in this situation. C<ref> is often
+useful to just test whether a value is a reference, which can be done
+by comparing the result to the empty string. It is a common mistake
+to use the result of C<ref> directly as a truth value: this goes wrong
+because C<0> (which is false) can be returned for a reference.
+
+If the operand is a reference to a blessed object, then the name of
+the class into which the referent is blessed will be returned. C<ref>
+doesn't care what the physical type of the referent is; blessing takes
+precedence over such concerns. Beware that exact comparison of C<ref>
+results against a class name doesn't perform a class membership test:
+a class's members also include objects blessed into subclasses, for
+which C<ref> will return the name of the subclass. Also beware that
+class names can clash with the built-in type names (described below).
+
+If the operand is a reference to an unblessed object, then the return
+value indicates the type of object. If the unblessed referent is not
+a scalar, then the return value will be one of the strings C<ARRAY>,
+C<HASH>, C<CODE>, C<FORMAT>, or C<IO>, indicating only which kind of
+object it is. If the unblessed referent is a scalar, then the return
+value will be one of the strings C<SCALAR>, C<VSTRING>, C<REF>, C<GLOB>,
+C<LVALUE>, or C<REGEXP>, depending on the kind of value the scalar
+currently has. Beware that these built-in type names can also be used as
+class names, so C<ref> returning one of these names doesn't unambiguously
+indicate that the referent is of the kind to which the name refers.
+
+The ambiguity between built-in type names and class names significantly
+limits the utility of C<ref>. For unambiguous information, use
+L<C<Scalar::Util::blessed()>|Scalar::Util/blessed> for information about
+blessing, and L<C<Scalar::Util::reftype()>|Scalar::Util/reftype> for
+information about physical types. Use L<the C<isa> method|UNIVERSAL/C<<
+$obj->isa( TYPE ) >>> for class membership tests, though one must be
+sure of blessedness before attempting a method call.
+
+See also L<perlref> and L<perlobj>.
=item rename OLDNAME,NEWNAME
X<rename> X<move> X<mv> X<ren>
Demands a version of Perl specified by VERSION, or demands some semantics
specified by EXPR or by L<C<$_>|perlvar/$_> if EXPR is not supplied.
-VERSION may be either a numeric argument such as 5.006, which will be
-compared to L<C<$]>|perlvar/$]>, or a literal of the form v5.6.1, which
-will be compared to L<C<$^V>|perlvar/$^V> (or C<$PERL_VERSION> in
-L<English>). An exception is raised if VERSION is greater than the
-version of the current Perl interpreter. Compare with
+VERSION may be either a literal such as v5.24.1, which will be
+compared to L<C<$^V>|perlvar/$^V> (or C<$PERL_VERSION> in L<English>),
+or a numeric argument of the form 5.024001, which will be compared to
+L<C<$]>|perlvar/$]>. An exception is raised if VERSION is greater than
+the version of the current Perl interpreter. Compare with
L<C<use>|/use Module VERSION LIST>, which can do a similar check at
compile time.
-Specifying VERSION as a literal of the form v5.6.1 should generally be
-avoided, because it leads to misleading error messages under earlier
-versions of Perl that do not support this syntax. The equivalent numeric
-version should be used instead.
+Specifying VERSION as a numeric argument of the form 5.024001 should
+generally be avoided as older less readable syntax compared to
+v5.24.1. Before perl 5.8.0 (released in 2002), the more verbose numeric
+form was the only supported syntax, which is why you might see it in
+older code.
- require v5.6.1; # run time version check
- require 5.6.1; # ditto
- require 5.006_001; # ditto; preferred for backwards
- compatibility
+ require v5.24.1; # run time version check
+ require 5.24.1; # ditto
+ require 5.024_001; # ditto; older syntax compatible
+ with perl 5.6
Otherwise, L<C<require>|/require VERSION> demands that a library file be
included if it hasn't already been included. The file is included via
If EXPR is a bareword, L<C<require>|/require VERSION> assumes a F<.pm>
extension and replaces C<::> with C</> in the filename for you,
to make it easy to load standard modules. This form of loading of
-modules does not risk altering your namespace.
+modules does not risk altering your namespace, however it will autovivify
+the stash for the required module.
In other words, if you try this:
require Foo::Bar; # a splendid bareword
The require function will actually look for the F<Foo/Bar.pm> file in the
-directories specified in the L<C<@INC>|perlvar/@INC> array.
+directories specified in the L<C<@INC>|perlvar/@INC> array, and it will
+autovivify the C<Foo::Bar::> stash at compile time.
But if you try this:
eval "require $class";
+or you could do
+
+ require "Foo/Bar.pm";
+
+Neither of these forms will autovivify any stashes at compile time and
+only have run time effects.
+
Now that you understand how L<C<require>|/require VERSION> looks for
files with a bareword argument, there is a little extra functionality
going on behind the scenes. Before L<C<require>|/require VERSION> looks
for a F<.pm> extension, it will first look for a similar filename with a
F<.pmc> extension. If this file is found, it will be loaded in place of
-any file ending in a F<.pm> extension.
+any file ending in a F<.pm> extension. This applies to both the explicit
+C<require "Foo/Bar.pm";> form and the C<require Foo::Bar;> form.
You can also insert hooks into the import facility by putting Perl code
directly into the L<C<@INC>|perlvar/@INC> array. There are three forms
line as read in L<C<$_>|perlvar/$_>.
Again, return 1 for each valid line, and 0 after all lines have been
returned.
+For historical reasons the subroutine will receive a meaningless argument
+(in fact always the numeric value zero) as C<$_[0]>.
=item 4
-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]>.
+Optional state for the subroutine. The state is passed in as C<$_[1]>.
=back
loop to clear variables and reset C<m?pattern?> searches so that they
work again. The
expression is interpreted as a list of single characters (hyphens
-allowed for ranges). All variables and arrays beginning with one of
+allowed for ranges). All variables (scalars, arrays, and hashes)
+in the current package beginning with one of
those letters are reset to their pristine state. If the expression is
omitted, one-match searches (C<m?pattern?>) are reset to match again.
Only resets variables or searches in the current package. Always returns
Resetting C<"A-Z"> is not recommended because you'll wipe out your
L<C<@ARGV>|perlvar/@ARGV> and L<C<@INC>|perlvar/@INC> arrays and your
L<C<%ENV>|perlvar/%ENV> hash.
+
Resets only package variables; lexical variables are unaffected, but
they clean themselves up on scope exit anyway, so you'll probably want
to use them instead. See L<C<my>|/my VARLIST>.
or the undefined value on error. The L<sendmsg(2)> syscall is currently
unimplemented. See L<perlipc/"UDP: Message Passing"> for examples.
-Note the I<characters>: depending on the status of the socket, either
-(8-bit) bytes or characters are sent. By default all sockets operate
-on bytes, but for example if the socket has been changed using
-L<C<binmode>|/binmode FILEHANDLE, LAYER> to operate with the
-C<:encoding(UTF-8)> I/O layer (see L<C<open>|/open FILEHANDLE,EXPR>, or
-the L<open> pragma), the I/O will operate on UTF-8
-encoded Unicode characters, not bytes. Similarly for the C<:encoding>
-layer: in that case pretty much any characters can be sent.
+Note that if the socket has been marked as C<:utf8>, C<send> will
+throw an exception. The C<:encoding(...)> layer implicitly introduces
+the C<:utf8> layer. See L<C<binmode>|/binmode FILEHANDLE, LAYER>.
=item setpgrp PID,PGRP
X<setpgrp> X<group>
Portability issues: L<perlport/socketpair>.
=item sort SUBNAME LIST
-X<sort> X<qsort> X<quicksort> X<mergesort>
+X<sort>
=item sort BLOCK LIST
actually modifies the element in the original list. This is usually
something to be avoided when writing clear code.
-Perl 5.6 and earlier used a quicksort algorithm to implement sort.
-That algorithm was not stable and I<could> go quadratic. (A I<stable> sort
-preserves the input order of elements that compare equal. Although
-quicksort's run time is O(NlogN) when averaged over all arrays of
-length N, the time can be O(N**2), I<quadratic> behavior, for some
-inputs.) In 5.7, the quicksort implementation was replaced with
-a stable mergesort algorithm whose worst-case behavior is O(NlogN).
-But benchmarks indicated that for some inputs, on some platforms,
-the original quicksort was faster. 5.8 has a L<sort> pragma for
-limited control of the sort. Its rather blunt control of the
-underlying algorithm may not persist into future Perls, but the
-ability to characterize the input or output in implementation
-independent ways quite probably will.
+Historically Perl has varied in whether sorting is stable by default.
+If stability matters, it can be controlled explicitly by using the
+L<sort> pragma.
Examples:
package main;
my @new = sort Other::backwards @old;
- # guarantee stability, regardless of algorithm
+ # guarantee stability
use sort 'stable';
my @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;
- # force use of mergesort (not portable outside Perl 5.8)
- use sort '_mergesort'; # note discouraging _
- my @new = sort { substr($a, 3, 5) cmp substr($b, 3, 5) } @old;
-
Warning: syntactical care is required when sorting the list returned from
a function. If you want to sort the list returned by the function call
C<find_records(@key)>, you can use:
# prints tinysmallnormalbighuge
-C<$a> and C<$b> are implicitely local to the sort() execution and regain their
+C<$a> and C<$b> are implicitly local to the sort() execution and regain their
former values upon completing the sort.
Sort subroutines written using C<$a> and C<$b> are bound to their calling
h interpret integer as C type "short" or
"unsigned short"
j interpret integer as C type "intmax_t" on Perl
- 5.14 or later, and only with a C99 compiler
- (unportable)
+ 5.14 or later; and only with a C99 compiler
+ prior to Perl 5.30 (unportable)
l interpret integer as C type "long" or
"unsigned long"
q, L, or ll interpret integer as C type "long long",
There is no syseof() function, which is ok, since
L<C<eof>|/eof FILEHANDLE> doesn't work well on device files (like ttys)
anyway. Use L<C<sysread>|/sysread FILEHANDLE,SCALAR,LENGTH,OFFSET> and
-check for a return value for 0 to decide whether you're done.
+check for a return value of 0 to decide whether you're done.
-Note that if the filehandle has been marked as C<:utf8>, Unicode
-characters are read instead of bytes (the LENGTH, OFFSET, and the
-return value of L<C<sysread>|/sysread FILEHANDLE,SCALAR,LENGTH,OFFSET>
-are in Unicode characters). The C<:encoding(...)> layer implicitly
+Note that if the filehandle has been marked as C<:utf8>, C<sysread> will
+throw an exception. The C<:encoding(...)> layer implicitly
introduces the C<:utf8> layer. See
L<C<binmode>|/binmode FILEHANDLE, LAYER>,
L<C<open>|/open FILEHANDLE,EXPR>, and the L<open> pragma.
that many characters counting backwards from the end of the string.
If SCALAR is of length zero, you can only use an OFFSET of 0.
-B<WARNING>: If the filehandle is marked C<:utf8>, Unicode characters
-encoded in UTF-8 are written instead of bytes, and the LENGTH, OFFSET, and
-return value of L<C<syswrite>|/syswrite FILEHANDLE,SCALAR,LENGTH,OFFSET>
-are in (UTF8-encoded Unicode) characters.
+B<WARNING>: If the filehandle is marked C<:utf8>, C<syswrite> will raise an exception.
The C<:encoding(...)> layer implicitly introduces the C<:utf8> layer.
Alternately, if the handle is not marked with an encoding but you
attempt to write characters with code points over 255, raises an exception.
bits, or three octal digits: C<0750> (the leading 0 indicates octal
and isn't one of the digits). The L<C<umask>|/umask EXPR> value is such
a number representing disabled permissions bits. The permission (or
-"mode") values you pass L<C<mkdir>|/mkdir FILENAME,MASK> or
+"mode") values you pass L<C<mkdir>|/mkdir FILENAME,MODE> or
L<C<sysopen>|/sysopen FILEHANDLE,FILENAME,MODE> are modified by your
umask, so even if you tell
L<C<sysopen>|/sysopen FILEHANDLE,FILENAME,MODE> to create a file with
Here's some advice: supply a creation mode of C<0666> for regular
files (in L<C<sysopen>|/sysopen FILEHANDLE,FILENAME,MODE>) and one of
-C<0777> for directories (in L<C<mkdir>|/mkdir FILENAME,MASK>) and
+C<0777> for directories (in L<C<mkdir>|/mkdir FILENAME,MODE>) and
executable files. This gives users the freedom of
choice: if they want protected files, they might choose process umasks
of C<022>, C<027>, or even the particularly antisocial mask of C<077>.
except that Module I<must> be a bareword.
The importation can be made conditional by using the L<if> module.
-In the peculiar C<use VERSION> form, VERSION may be either a positive
-decimal fraction such as 5.006, which will be compared to
-L<C<$]>|perlvar/$]>, or a v-string of the form v5.6.1, which will be
-compared to L<C<$^V>|perlvar/$^V> (aka $PERL_VERSION). An
-exception is raised if VERSION is greater than the version of the
-current Perl interpreter; Perl will not attempt to parse the rest of the
-file. Compare with L<C<require>|/require VERSION>, which can do a
-similar check at run time.
-Symmetrically, C<no VERSION> allows you to specify that you want a version
-of Perl older than the specified one.
-
-Specifying VERSION as a literal of the form v5.6.1 should generally be
-avoided, because it leads to misleading error messages under earlier
-versions of Perl (that is, prior to 5.6.0) that do not support this
-syntax. The equivalent numeric version should be used instead.
-
- use v5.6.1; # compile time version check
- use 5.6.1; # ditto
- use 5.006_001; # ditto; preferred for backwards compatibility
+In the C<use VERSION> form, VERSION may be either a v-string such as
+v5.24.1, which will be compared to L<C<$^V>|perlvar/$^V> (aka
+$PERL_VERSION), or a numeric argument of the form 5.024001, which will
+be compared to L<C<$]>|perlvar/$]>. An exception is raised if VERSION
+is greater than the version of the current Perl interpreter; Perl will
+not attempt to parse the rest of the file. Compare with
+L<C<require>|/require VERSION>, which can do a similar check at run
+time. Symmetrically, C<no VERSION> allows you to specify that you
+want a version of Perl older than the specified one.
+
+Specifying VERSION as a numeric argument of the form 5.024001 should
+generally be avoided as older less readable syntax compared to
+v5.24.1. Before perl 5.8.0 released in 2002 the more verbose numeric
+form was the only supported syntax, which is why you might see it in
+
+ use v5.24.1; # compile time version check
+ use 5.24.1; # ditto
+ use 5.024_001; # ditto; older syntax compatible with perl 5.6
This is often useful if you need to check the current Perl version before
L<C<use>|/use Module VERSION LIST>ing library modules that won't work
inherited from the L<C<UNIVERSAL>|UNIVERSAL> class, croaks if the given
version is larger than the value of the variable C<$Module::VERSION>.
+The VERSION argument cannot be an arbitrary expression. It only counts
+as a VERSION argument if it is a version number literal, starting with
+either a digit or C<v> followed by a digit. Anything that doesn't
+look like a version literal will be parsed as the start of the LIST.
+Nevertheless, many attempts to use an arbitrary expression as a VERSION
+argument will appear to work, because L<Exporter>'s C<import> method
+handles numeric arguments specially, performing version checks rather
+than treating them as things to export.
+
Again, there is a distinction between omitting LIST (L<C<import>|/import
LIST> called with no arguments) and an explicit empty LIST C<()>
(L<C<import>|/import LIST> not called). Note that there is no comma
use strict qw(subs vars refs);
use subs qw(afunc blurfl);
use warnings qw(all);
- use sort qw(stable _quicksort _mergesort);
+ use sort qw(stable);
Some of these pseudo-modules import semantics into the current
block scope (like L<C<strict>|strict> or L<C<integer>|integer>, unlike
insertion and deletion of items.
As a side effect, calling L<C<values>|/values HASH> resets the HASH or
-ARRAY's internal iterator, see L<C<each>|/each HASH>. (In particular,
+ARRAY's internal iterator (see L<C<each>|/each HASH>) before yielding the
+values. In particular,
calling L<C<values>|/values HASH> in void context resets the iterator
-with no other overhead. Apart from resetting the iterator,
+with no other overhead.
+
+Apart from resetting the iterator,
C<values @array> in list context is the same as plain C<@array>.
(We recommend that you use void context C<keys @array> for this, but
reasoned that taking C<values @array> out would require more
=for Pod::Functions print debugging info
-Prints the value of LIST to STDERR. If the last element of LIST does
-not end in a newline, it appends the same file/line number text as
-L<C<die>|/die LIST> does.
-
-If the output is empty and L<C<$@>|perlvar/$@> already contains a value
-(typically from a previous eval) that value is used after appending
-C<"\t...caught"> to L<C<$@>|perlvar/$@>. This is useful for staying
-almost, but not entirely similar to L<C<die>|/die LIST>.
-
-If L<C<$@>|perlvar/$@> is empty, then the string
-C<"Warning: Something's wrong"> is used.
-
-No message is printed if there is a L<C<$SIG{__WARN__}>|perlvar/%SIG>
-handler
-installed. It is the handler's responsibility to deal with the message
+Emits a warning, usually by printing it to C<STDERR>. C<warn> interprets
+its operand LIST in the same way as C<die>, but is slightly different
+in what it defaults to when LIST is empty or makes an empty string.
+If it is empty and L<C<$@>|perlvar/$@> already contains an exception
+value then that value is used after appending C<"\t...caught">. If it
+is empty and C<$@> is also empty then the string C<"Warning: Something's
+wrong"> is used.
+
+By default, the exception derived from the operand LIST is stringified
+and printed to C<STDERR>. This behaviour can be altered by installing
+a L<C<$SIG{__WARN__}>|perlvar/%SIG> handler. If there is such a
+handler then no message is automatically printed; it is the handler's
+responsibility to deal with the exception
as it sees fit (like, for instance, converting it into a
L<C<die>|/die LIST>). Most
handlers must therefore arrange to actually display the
https://perl5.git.perl.org / perl5.git / blobdiff