number of characters removed from all its arguments. It's often used to
remove the newline from the end of an input record when you're worried
that the final record may be missing its newline. When in paragraph
-mode (C<$/ = "">), it removes all trailing newlines from the string.
+mode (C<$/ = ''>), it removes all trailing newlines from the string.
When in slurp mode (C<$/ = undef>) or fixed-length record mode (C<$/> is
a reference to an integer or the like; see L<perlvar>) chomp() won't
remove anything.
still tests true for exists(), or to 0 if none do. In other words, an
array won't have trailing nonexistent elements after a delete.
-B<WARNING:> Calling delete on array values is deprecated and likely to
-be removed in a future version of Perl.
+B<WARNING:> Calling C<delete> on array values is strongly discouraged. The
+notion of deleting or checking the existence of Perl array elements is not
+conceptually coherent, and can lead to surprising behavior.
Deleting from C<%ENV> modifies the environment. Deleting from a hash tied to
a DBM file deletes the entry from the DBM file. Deleting from a C<tied> hash
print "$key=$value\n";
}
-Starting with Perl 5.14, C<each> can take a scalar EXPR, which must hold
+Starting with Perl 5.14, C<each> can take a scalar EXPR, which must hold a
reference to an unblessed hash or array. The argument will be dereferenced
automatically. This aspect of C<each> is considered highly experimental.
The exact behaviour may change in a future version of Perl.
print "True\n" if $hash{$key};
exists may also be called on array elements, but its behavior is much less
-obvious and is strongly tied to the use of L</delete> on arrays. B<Be aware>
-that calling exists on array values is deprecated and likely to be removed in
-a future version of Perl.
+obvious and is strongly tied to the use of L</delete> on arrays.
+
+B<WARNING:> Calling C<exists> on array values is strongly discouraged. The
+notion of deleting or checking the existence of Perl array elements is not
+conceptually coherent, and can lead to surprising behavior.
print "Exists\n" if exists $array[$index];
print "Defined\n" if defined $array[$index];
"not have a real file descriptor\n";
}
+The behavior of C<fileno> on a directory handle depends on the operating
+system. On a system with dirfd(3) or similar, C<fileno> on a directory
+handle returns the underlying file descriptor associated with the
+handle; on systems with no such support, it returns the undefined value,
+and sets C<$!> (errno).
+
=item flock FILEHANDLE,OPERATION
X<flock> X<lock> X<locking>
$comment, $gcos, $dir, $shell, $expire ) = getpw*
# 5 6 7 8 9
-(If the entry doesn't exist you get an empty list.)
+(If the entry doesn't exist, the return value is a single meaningless true
+value.)
The exact meaning of the $gcos field varies but it usually contains
the real name of the user (as opposed to the login name) and other
rules for the remaining code points (this last can only happen if
the UTF8 flag is also set). See L<perllocale>.
-Starting in v5.20, Perl wil use full Unicode rules if the locale is
+Starting in v5.20, Perl uses full Unicode rules if the locale is
UTF-8. Otherwise, there is a deficiency in this scheme, which is that
case changes that cross the 255/256
boundary are not well-defined. For example, the lower case of LATIN CAPITAL
itself, because 0xDF may not be LATIN SMALL LETTER SHARP S in the
current locale, and Perl has no way of knowing if that character even
exists in the locale, much less what code point it is. Perl returns
-the input character unchanged, for all instances (and there aren't
-many) where the 255/256 boundary would otherwise be crossed.
+a result that is above 255 (almost always the input character unchanged,
+for all instances (and there aren't many) where the 255/256 boundary
+would otherwise be crossed; and starting in v5.22, it raises a
+L<locale|perldiag/Can't do %s("%s") on non-UTF-8 locale; resolved to "%s".> warning.
=item Otherwise, If EXPR has the UTF8 flag set:
doesn't it won't realize something is wrong until it gets to the C<}> and
encounters the missing (or unexpected) comma. The syntax error will be
reported close to the C<}>, but you'll need to change something near the C<{>
-such as using a unary C<+> to give Perl some help:
+such as using a unary C<+> or semicolon to give Perl some help:
%hash = map { "\L$_" => 1 } @array # perl guesses EXPR. wrong
%hash = map { +"\L$_" => 1 } @array # perl guesses BLOCK. right
- %hash = map { ("\L$_" => 1) } @array # this also works
- %hash = map { lc($_) => 1 } @array # as does this.
+ %hash = map {; "\L$_" => 1 } @array # this also works
+ %hash = map { ("\L$_" => 1) } @array # as does this
+ %hash = map { lc($_) => 1 } @array # and this.
%hash = map +( lc($_) => 1 ), @array # this is EXPR and works!
%hash = map ( lc($_), 1 ), @array # evaluates to (1, @array)
This means that when C<use strict 'vars'> is in effect, C<our> lets you use
a package variable without qualifying it with the package name, but only within
-the lexical scope of the C<our> declaration.
+the lexical scope of the C<our>
+declaration. This applies immediately--even
+within the same statement.
package Foo;
use strict;
print $Foo::foo; # prints 23
+Because the variable becomes legal immediately under C<use strict 'vars'>, so
+long as there is no variable with that name is already in scope, you can then
+reference the package variable again even within the same statement.
+
+ package Foo;
+ use strict;
+
+ my $foo = $foo; # error, undeclared $foo on right-hand side
+ our $foo = $foo; # no errors
+
If more than one variable is listed, the list must be placed
in parentheses.
0x56 0x78 0x12 0x34
0x34 0x12 0x78 0x56
+These are called mid-endian, middle-endian, mixed-endian, or just weird.
+
You can determine your system endianness with this incantation:
printf("%#02x ", $_) for unpack("W*", pack L=>0x12345678);
$ perl -V:byteorder
Byteorders C<"1234"> and C<"12345678"> are little-endian; C<"4321">
-and C<"87654321"> are big-endian.
+and C<"87654321"> are big-endian. Systems with multiarchitecture binaries
+will have C<"ffff">, signifying that static information doesn't work,
+one must use runtime probing.
For portably packed integers, either use the formats C<n>, C<N>, C<v>,
and C<V> or else use the C<< > >> and C<< < >> modifiers described
=item *
+Also floating point numbers have endianness. Usually (but not always)
+this agrees with the integer endianness. Even though most platforms
+these days use the IEEE 754 binary format, there are differences,
+especially if the long doubles are involved. You can see the
+C<Config> variables C<doublekind> and C<longdblkind> (also C<doublesize>,
+C<longdblsize>): the "kind" values are enums, unlike C<byteorder>.
+
+Portability-wise the best option is probably to keep to the IEEE 754
+64-bit doubles, and of agreed-upon endianness. Another possibility
+is the C<"%a">) format of C<printf>.
+
+=item *
+
Starting with Perl 5.10.0, integer and floating-point formats, along with
the C<p> and C<P> formats and C<()> groups, may all be followed by the
C<< > >> or C<< < >> endianness modifiers to respectively enforce big-
=item *
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)
+the packed string is processed per character, and UTF-8 byte 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
assumes additional C<""> arguments. If TEMPLATE requires fewer arguments
than given, extra arguments are ignored.
+=item *
+
+Attempting to pack the special floating point values C<Inf> and C<NaN>
+(infinity, also in negative, and not-a-number) into packed integer values
+(like C<"L">) is a fatal error. The reason for this is that there simply
+isn't any sensible mapping for these special values into integers.
+
=back
Examples:
=item prototype FUNCTION
X<prototype>
+=item prototype
+
=for Pod::Functions +5.002 get the prototype (if any) of a subroutine
Returns the prototype of a function as a string (or C<undef> if the
function has no prototype). FUNCTION is a reference to, or the name of,
-the function whose prototype you want to retrieve.
+the function whose prototype you want to retrieve. If FUNCTION is omitted,
+$_ is used.
If FUNCTION is a string starting with C<CORE::>, the rest is taken as a
name for a Perl builtin. If the builtin's arguments
# same thing, but much more efficiently;
# we'll build auxiliary indices instead
# for speed
- my @nums = @caps = ();
+ my (@nums, @caps);
for (@old) {
push @nums, ( /=(\d+)/ ? $1 : undef );
push @caps, fc($_);
@result = sort { $a <=> $b } grep { $_ == $_ } @input;
-=item splice ARRAY or EXPR,OFFSET,LENGTH,LIST
+=item splice ARRAY,OFFSET,LENGTH,LIST
X<splice>
-=item splice ARRAY or EXPR,OFFSET,LENGTH
+=item splice ARRAY,OFFSET,LENGTH
+
+=item splice ARRAY,OFFSET
+
+=item splice ARRAY
-=item splice ARRAY or EXPR,OFFSET
+=item splice EXPR,OFFSET,LENGTH,LIST
-=item splice ARRAY or EXPR
+=item splice EXPR,OFFSET,LENGTH
+
+=item splice EXPR,OFFSET
+
+=item splice EXPR
=for Pod::Functions add or remove elements anywhere in an array
list of its component characters.
As a special case for C<split>, the empty pattern given in
-L<match operator|perlop/"m/PATTERN/msixpodualgc"> syntax (C<//>) specifically matches the empty string, which is contrary to its usual
+L<match operator|perlop/"m/PATTERN/msixpodualngc"> syntax (C<//>)
+specifically matches the empty string, which is contrary to its usual
interpretation as the last successful match.
If PATTERN is C</^/>, then it is treated as if it used the
C<state> variables are enabled only when the C<use feature "state"> pragma
is in effect, unless the keyword is written as C<CORE::state>.
-See also L<feature>.
+See also L<feature>. Alternately, include a C<use v5.10> or later to the
+current scope.
=item study SCALAR
X<study>
=for Pod::Functions optimize input data for repeated searches
-Takes extra time to study SCALAR (C<$_> if unspecified) in anticipation of
-doing many pattern matches on the string before it is next modified.
+May take extra time to study SCALAR (C<$_> if unspecified) in anticipation
+of doing many pattern matches on the string before it is next modified.
This may or may not save time, depending on the nature and number of
patterns you are searching and the distribution of character
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.
+
+Note that since Perl version 5.16 this function has been a no-op, but
+this might change in a future release.
+
(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,
function calls the underlying operating system's I<open>(2) function with the
parameters FILENAME, MODE, and PERMS.
+Returns true on success and C<undef> otherwise.
+
The possible values and flag bits of the MODE parameter are
system-dependent; they are available via the standard module C<Fcntl>. See
the documentation of your operating system's I<open>(2) syscall to see
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.)
-C<use VERSION> also enables all features available in the requested
+C<use VERSION> also lexically enables all features available in the requested
version as defined by the C<feature> pragma, disabling any features
not in the requested version's feature bundle. See L<feature>.
Similarly, if the specified Perl version is greater than or equal to
5.12.0, 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.
+before it. Later use of C<use VERSION>
+will override all behavior of a previous
+C<use VERSION>, possibly removing the C<strict> and C<feature> added by
+C<use VERSION>. C<use VERSION> does not
+load the F<feature.pm> or F<strict.pm>
+files.
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
Note that a return value of C<-1> could mean that child processes are
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.
+If you use C<wait> in your handler for $SIG{CHLD}, it may accidentally wait
+
for the child created by qx() or system(). See L<perlipc> for details.
Portability issues: L<perlport/wait>.
https://perl5.git.perl.org / perl5.git / blobdiff