X-Git-Url: https://perl5.git.perl.org/perl5.git/blobdiff_plain/d7c042c9f3475e045bbea4f4880efff973b7049d..2cb35ee012cfe486aa75a422e7bb3cb18ff51336:/pod/perlvar.pod
diff --git a/pod/perlvar.pod b/pod/perlvar.pod
index eb7468f..257fdb6 100644
--- a/pod/perlvar.pod
+++ b/pod/perlvar.pod
@@ -12,40 +12,40 @@ arbitrarily long (up to an internal limit of 251 characters) and
may contain letters, digits, underscores, or the special sequence
C<::> or C<'>. In this case, the part before the last C<::> or
C<'> is taken to be a I; see L.
-
-Perl variable names may also be a sequence of digits or a single
-punctuation or control character. These names are all reserved for
+A Unicode letter that is not ASCII is not considered to be a letter
+unless S> is in effect, and somewhat more complicated
+rules apply; see L for details.
+
+Perl variable names may also be a sequence of digits, a single
+punctuation character, or the two-character sequence: C<^> (caret or
+CIRCUMFLEX ACCENT) followed by any one of the characters C<[][A-Z^_?\]>.
+These names are all reserved for
special uses by Perl; for example, the all-digits names are used
to hold data captured by backreferences after a regular expression
-match. Perl has a special syntax for the single-control-character
-names: It understands C<^X> (caret C) to mean the control-C
-character. For example, the notation C<$^W> (dollar-sign caret
-C) is the scalar variable whose name is the single character
-control-C. This is better than typing a literal control-C
-into your program.
-
-Since Perl 5.6, Perl variable names may be alphanumeric
-strings that begin with control characters (or better yet, a caret).
-These variables must be written in the form C<${^Foo}>; the braces
-are not optional. C<${^Foo}> denotes the scalar variable whose
-name is a control-C followed by two C's. These variables are
+match.
+
+Since Perl v5.6.0, Perl variable names may also be alphanumeric strings
+preceded by a caret. These must all be written in the form C<${^Foo}>;
+the braces are not optional. C<${^Foo}> denotes the scalar variable
+whose name is considered to be a control-C followed by two C's.
+These variables are
reserved for future special uses by Perl, except for the ones that
-begin with C<^_> (control-underscore or caret-underscore). No
-control-character name that begins with C<^_> will acquire a special
+begin with C<^_> (caret-underscore). No
+name that begins with C<^_> will acquire a special
meaning in any future version of Perl; such names may therefore be
used safely in programs. C<$^_> itself, however, I reserved.
-Perl identifiers that begin with digits, control characters, or
+Perl identifiers that begin with digits or
punctuation characters are exempt from the effects of the C
declaration and are always forced to be in package C; they are
also exempt from C errors. A few other names are also
exempt in these ways:
- ENV STDIN
- INC STDOUT
- ARGV STDERR
- ARGVOUT
- SIG
+ ENV STDIN
+ INC STDOUT
+ ARGV STDERR
+ ARGVOUT
+ SIG
In particular, the special C<${^_XYZ}> variables are always taken
to be in package C, regardless of any C declarations
@@ -57,15 +57,11 @@ The following names have special meaning to Perl. Most punctuation
names have reasonable mnemonics, or analogs in the shells.
Nevertheless, if you wish to use long variable names, you need only say:
- use English;
+ use English;
at the top of your program. This aliases all the short names to the long
names in the current package. Some even have medium names, generally
-borrowed from B. To avoid a performance hit, if you don't need the
-C<$PREMATCH>, C<$MATCH>, or C<$POSTMATCH> it's best to use the C
-module without them:
-
- use English '-no_match_vars';
+borrowed from B. For more info, please see L.
Before you continue, note the sort order for variables. In general, we
first list the variables in case-insensitive, almost-lexigraphical
@@ -86,17 +82,17 @@ X<$_> X<$ARG>
The default input and pattern-searching space. The following pairs are
equivalent:
- while (<>) {...} # equivalent only in while!
- while (defined($_ = <>)) {...}
+ while (<>) {...} # equivalent only in while!
+ while (defined($_ = <>)) {...}
- /^Subject:/
- $_ =~ /^Subject:/
+ /^Subject:/
+ $_ =~ /^Subject:/
- tr/a-z/A-Z/
- $_ =~ tr/a-z/A-Z/
+ tr/a-z/A-Z/
+ $_ =~ tr/a-z/A-Z/
- chomp
- chomp($_)
+ chomp
+ chomp($_)
Here are the places where Perl will assume C<$_> even if you don't use it:
@@ -107,10 +103,11 @@ Here are the places where Perl will assume C<$_> even if you don't use it:
The following functions use C<$_> as a default argument:
abs, alarm, chomp, chop, chr, chroot,
-cos, defined, eval, evalbytes, exp, glob,
-hex, int, lc, lcfirst, length, log, lstat, mkdir, oct, ord, pos, print,
+cos, defined, eval, evalbytes, exp, fc, glob, hex, int, lc,
+lcfirst, length, log, lstat, mkdir, oct, ord, pos, print, printf,
quotemeta, readlink, readpipe, ref, require, reverse (in scalar context only),
-rmdir, sin, split (on its second argument), sqrt, stat, study, uc, ucfirst,
+rmdir, say, sin, split (for its second
+argument), sqrt, stat, study, uc, ucfirst,
unlink, unpack.
=item *
@@ -138,16 +135,26 @@ The implicit variable of C.
=item *
-The default place to put an input record when a C<< >>
+The default place to put the next value or input record
+when a C<< >>, C, C or C
operation's result is tested by itself as the sole criterion of a C
test. Outside a C test, this will not happen.
=back
-As C<$_> is a global variable, this may lead in some cases to unwanted
-side-effects. As of perl 5.10, you can now use a lexical version of
+C<$_> is by default a global variable. However, as
+of perl v5.10.0, you can use a lexical version of
C<$_> by declaring it in a file or in a block with C. Moreover,
-declaring C restores the global C<$_> in the current scope.
+declaring C restores the global C<$_> in the current scope. Though
+this seemed like a good idea at the time it was introduced, lexical C<$_>
+actually causes more problems than it solves. If you call a function that
+expects to be passed information via C<$_>, it may or may not work,
+depending on how the function is written, there not being any easy way to
+solve this. Just avoid lexical C<$_>, unless you are feeling particularly
+masochistic. For this reason lexical C<$_> is still experimental and will
+produce a warning unless warnings have been disabled. As with other
+experimental features, the behavior of lexical C<$_> is subject to change
+without notice, including change into a fatal error.
Mnemonic: underline is understood in certain operations.
@@ -158,7 +165,7 @@ X<@_> X<@ARG>
Within a subroutine the array C<@_> contains the parameters passed to
that subroutine. Inside a subroutine, C<@_> is the default array for
-the array operators C, C, C, and C.
+the array operators C and C.
See L.
@@ -171,11 +178,11 @@ When an array or an array slice is interpolated into a double-quoted
string or a similar context such as C, its elements are
separated by this value. Default is a space. For example, this:
- print "The array is: @array\n";
+ print "The array is: @array\n";
is equivalent to this:
- print "The array is: " . join($", @array) . "\n";
+ print "The array is: " . join($", @array) . "\n";
Mnemonic: works in double-quoted context.
@@ -196,7 +203,7 @@ would emulate POSIX semantics on Linux systems using LinuxThreads, a
partial implementation of POSIX Threads that has since been superseded
by the Native POSIX Thread Library (NPTL).
-LinuxThreads is now obsolete on Linux, and and caching C
+LinuxThreads is now obsolete on Linux, and caching C
like this made embedding perl unnecessarily complex (since you'd have
to manually update the value of $$), so now C<$$> and C
will always return the same values as the underlying C library.
@@ -207,7 +214,7 @@ semantics, which are POSIX-like.
To see if your system is affected by this discrepancy check if
C returns a false
-value. NTPL threads preserve the POSIX semantics.
+value. NTPL threads preserve the POSIX semantics.
Mnemonic: same as shells.
@@ -250,7 +257,7 @@ have their own copies of it.
If the program has been given to perl via the switches C<-e> or C<-E>,
C<$0> will contain the string C<"-e">.
-On Linux as of perl 5.14 the legacy process name will be set with
+On Linux as of perl v5.14.0 the legacy process name will be set with
C, in addition to altering the POSIX name via C as
perl has done since version 4.000. Now system utilities that read the
legacy process name such as ps, top and killall will recognize the
@@ -341,8 +348,8 @@ X<< $> >> X<$EUID> X<$EFFECTIVE_USER_ID>
The effective uid of this process. For example:
- $< = $>; # set real to effective uid
- ($<,$>) = ($>,$<); # swap real and effective uids
+ $< = $>; # set real to effective uid
+ ($<,$>) = ($>,$<); # swap real and effective uids
You can change both the effective uid and the real uid at the same
time by using C. Changes to C<< $> >> require a check
@@ -363,19 +370,19 @@ X<$;> X<$SUBSEP> X
The subscript separator for multidimensional array emulation. If you
refer to a hash element as
- $foo{$a,$b,$c}
+ $foo{$x,$y,$z}
it really means
- $foo{join($;, $a, $b, $c)}
+ $foo{join($;, $x, $y, $z)}
But don't put
- @foo{$a,$b,$c} # a slice--note the @
+ @foo{$x,$y,$z} # a slice--note the @
which means
- ($foo{$a},$foo{$b},$foo{$c})
+ ($foo{$x},$foo{$y},$foo{$z})
Default is "\034", the same as SUBSEP in B. If your keys contain
binary data there might not be any safe value for C<$;>.
@@ -403,6 +410,67 @@ The hash C<%ENV> contains your current environment. Setting a
value in C changes the environment for any child processes
you subsequently C off.
+As of v5.18.0, both keys and values stored in C<%ENV> are stringified.
+
+ my $foo = 1;
+ $ENV{'bar'} = \$foo;
+ if( ref $ENV{'bar'} ) {
+ say "Pre 5.18.0 Behaviour";
+ } else {
+ say "Post 5.18.0 Behaviour";
+ }
+
+Previously, only child processes received stringified values:
+
+ my $foo = 1;
+ $ENV{'bar'} = \$foo;
+
+ # Always printed 'non ref'
+ system($^X, '-e',
+ q/print ( ref $ENV{'bar'} ? 'ref' : 'non ref' ) /);
+
+This happens because you can't really share arbitrary data structures with
+foreign processes.
+
+=item $OLD_PERL_VERSION
+
+=item $]
+X<$]> X<$OLD_PERL_VERSION>
+
+The revision, version, and subversion of the Perl interpreter, represented
+as a decimal of the form 5.XXXYYY, where XXX is the version / 1e3 and YYY
+is the subversion / 1e6. For example, Perl v5.10.1 would be "5.010001".
+
+This variable can be used to determine whether the Perl interpreter
+executing a script is in the right range of versions:
+
+ warn "No PerlIO!\n" if $] lt '5.008';
+
+When comparing C<$]>, string comparison operators are B. The inherent limitations of binary floating point
+representation can sometimes lead to incorrect comparisons for some
+numbers on some architectures.
+
+See also the documentation of C
match operator flag and the C<${^PREMATCH}>,
+C<${^MATCH}>, and C<${^POSTMATCH}> variables were introduced, that allowed
+you to suffer the penalties only on patterns marked with C.
-The C and C
-modules can help you find uses of these
-problematic match variables in your code.
+In Perl 5.18.0 onwards, perl started noting the presence of each of the
+three variables separately, and only copied that part of the string
+required; so in
-Since Perl 5.10, you can use the C match operator flag and the
-C<${^PREMATCH}>, C<${^MATCH}>, and C<${^POSTMATCH}> variables instead
-so you only suffer the performance penalties.
+ $`; $&; "abcdefgh" =~ /d/
+
+perl would only copy the "abcd" part of the string. That could make a big
+difference in something like
+
+ $str = 'x' x 1_000_000;
+ $&; # whoops
+ $str =~ /x/g # one char copied a million times, not a million chars
+
+In Perl 5.20.0 a new copy-on-write system was enabled by default, which
+finally fixes all performance issues with these three variables, and makes
+them safe to use anywhere.
+
+The C and C modules can help you
+find uses of these problematic match variables in your code.
=over 8
=item $> ($1, $2, ...)
-X<$1> X<$2> X<$3>
+X<$1> X<$2> X<$3> X<$I>
Contains the subpattern from the corresponding set of capturing
parentheses from the last successful pattern match, not counting patterns
matched in nested blocks that have been exited already.
+Note there is a distinction between a capture buffer which matches
+the empty string a capture buffer which is optional. Eg, C<(x?)> and
+C<(x)?> The latter may be undef, the former not.
+
These variables are read-only and dynamically-scoped.
Mnemonic: like \digits.
+=item @{^CAPTURE}
+X<@{^CAPTURE}> X<@^CAPTURE>
+
+An array which exposes the contents of the capture buffers, if any, of
+the last successful pattern match, not counting patterns matched
+in nested blocks that have been exited already.
+
+Note that the 0 index of @{^CAPTURE} is equivalent to $1, the 1 index
+is equivalent to $2, etc.
+
+ if ("foal"=~/(.)(.)(.)(.)/) {
+ print join "-", @{^CAPTURE};
+ }
+
+should output "f-o-a-l".
+
+See also L$I>, L%{^CAPTURE}> and L%{^CAPTURE_ALL}>.
+
+Note that unlike most other regex magic variables there is no single
+letter equivalent to C<@{^CAPTURE}>.
+
+This variable was added in 5.25.7
+
=item $MATCH
=item $&
@@ -807,11 +954,8 @@ The string matched by the last successful pattern match (not counting
any matches hidden within a BLOCK or C enclosed by the current
BLOCK).
-The use of this variable anywhere in a program imposes a considerable
-performance penalty on all regular expression matches. To avoid this
-penalty, you can extract the same substring by using L@->. Starting
-with Perl 5.10, you can use the C match flag and the C<${^MATCH}>
-variable to do the same thing for particular match operations.
+See L above for the serious performance implications
+of using this variable (even once) in your code.
This variable is read-only and dynamically-scoped.
@@ -821,11 +965,16 @@ Mnemonic: like C<&> in some editors.
X<${^MATCH}>
This is similar to C<$&> (C<$MATCH>) except that it does not incur the
-performance penalty associated with that variable, and is only guaranteed
+performance penalty associated with that variable.
+
+See L above.
+
+In Perl v5.18 and earlier, it is only guaranteed
to return a defined value when the pattern was compiled or executed with
-the C modifier.
+the C modifier. In Perl v5.20, the C modifier does nothing, so
+C<${^MATCH}> does the same thing as C<$MATCH>.
-This variable was added in Perl 5.10.
+This variable was added in Perl v5.10.0.
This variable is read-only and dynamically-scoped.
@@ -838,12 +987,8 @@ The string preceding whatever was matched by the last successful
pattern match, not counting any matches hidden within a BLOCK or C
enclosed by the current BLOCK.
-The use of this variable anywhere in a program imposes a considerable
-performance penalty on all regular expression matches. To avoid this
-penalty, you can extract the same substring by using L@->. Starting
-with Perl 5.10, you can use the C match flag and the
-C<${^PREMATCH}> variable to do the same thing for particular match
-operations.
+See L above for the serious performance implications
+of using this variable (even once) in your code.
This variable is read-only and dynamically-scoped.
@@ -853,11 +998,16 @@ Mnemonic: C<`> often precedes a quoted string.
X<$`> X<${^PREMATCH}>
This is similar to C<$`> ($PREMATCH) except that it does not incur the
-performance penalty associated with that variable, and is only guaranteed
+performance penalty associated with that variable.
+
+See L above.
+
+In Perl v5.18 and earlier, it is only guaranteed
to return a defined value when the pattern was compiled or executed with
-the C modifier.
+the C modifier. In Perl v5.20, the C modifier does nothing, so
+C<${^PREMATCH}> does the same thing as C<$PREMATCH>.
-This variable was added in Perl 5.10
+This variable was added in Perl v5.10.0.
This variable is read-only and dynamically-scoped.
@@ -870,16 +1020,12 @@ The string following whatever was matched by the last successful
pattern match (not counting any matches hidden within a BLOCK or C
enclosed by the current BLOCK). Example:
- local $_ = 'abcdefghi';
- /def/;
- print "$`:$&:$'\n"; # prints abc:def:ghi
+ local $_ = 'abcdefghi';
+ /def/;
+ print "$`:$&:$'\n"; # prints abc:def:ghi
-The use of this variable anywhere in a program imposes a considerable
-performance penalty on all regular expression matches.
-To avoid this penalty, you can extract the same substring by
-using L@->. Starting with Perl 5.10, you can use the C match flag
-and the C<${^POSTMATCH}> variable to do the same thing for particular
-match operations.
+See L above for the serious performance implications
+of using this variable (even once) in your code.
This variable is read-only and dynamically-scoped.
@@ -889,11 +1035,16 @@ Mnemonic: C<'> often follows a quoted string.
X<${^POSTMATCH}> X<$'> X<$POSTMATCH>
This is similar to C<$'> (C<$POSTMATCH>) except that it does not incur the
-performance penalty associated with that variable, and is only guaranteed
+performance penalty associated with that variable.
+
+See L above.
+
+In Perl v5.18 and earlier, it is only guaranteed
to return a defined value when the pattern was compiled or executed with
-the C modifier.
+the C modifier. In Perl v5.20, the C modifier does nothing, so
+C<${^POSTMATCH}> does the same thing as C<$POSTMATCH>.
-This variable was added in Perl 5.10.
+This variable was added in Perl v5.10.0.
This variable is read-only and dynamically-scoped.
@@ -906,7 +1057,7 @@ The text matched by the last bracket of the last successful search pattern.
This is useful if you don't know which one of a set of alternative patterns
matched. For example:
- /Version: (.*)|Revision: (.*)/ && ($rev = $+);
+ /Version: (.*)|Revision: (.*)/ && ($rev = $+);
This variable is read-only and dynamically-scoped.
@@ -925,12 +1076,12 @@ This is primarily used inside C<(?{...})> blocks for examining text
recently matched. For example, to effectively capture text to a variable
(in addition to C<$1>, C<$2>, etc.), replace C<(...)> with
- (?:(...)(?{ $var = $^N }))
+ (?:(...)(?{ $var = $^N }))
By setting and then using C<$var> in this way relieves you from having to
worry about exactly which numbered set of parentheses they are.
-This variable was added in Perl 5.8.
+This variable was added in Perl v5.8.0.
Mnemonic: the (possibly) Nested parenthesis that most recently closed.
@@ -950,12 +1101,14 @@ past where C<$2> ends, and so on. You can use C<$#+> to determine
how many subgroups were in the last successful match. See the
examples given for the C<@-> variable.
-This variable was added in Perl 5.6.
+This variable was added in Perl v5.6.0.
+
+=item %{^CAPTURE}
=item %LAST_PAREN_MATCH
=item %+
-X<%+> X<%LAST_PAREN_MATCH>
+X<%+> X<%LAST_PAREN_MATCH> X<%{^CAPTURE}>
Similar to C<@+>, the C<%+> hash allows access to the named capture
buffers, should they exist, in the last successful match in the
@@ -963,11 +1116,14 @@ currently active dynamic scope.
For example, C<$+{foo}> is equivalent to C<$1> after the following match:
- 'foo' =~ /(?foo)/;
+ 'foo' =~ /(?foo)/;
The keys of the C<%+> hash list only the names of buffers that have
captured (and that are thus associated to defined values).
+If multiple distinct capture groups have the same name, then
+C<$+{NAME}> will refer to the leftmost defined group in the match.
+
The underlying behaviour of C<%+> is provided by the
L module.
@@ -977,7 +1133,8 @@ iterative access to them via C may have unpredictable results.
Likewise, if the last successful match changes, then the results may be
surprising.
-This variable was added in Perl 5.10.
+This variable was added in Perl v5.10.0. The C<%{^CAPTURE}> alias was
+added in 5.25.7.
This variable is read-only and dynamically-scoped.
@@ -1023,12 +1180,13 @@ After a match against some variable C<$var>:
=back
-This variable was added in Perl 5.6.
+This variable was added in Perl v5.6.0.
-=item %LAST_MATCH_START
+=item %{^CAPTURE_ALL}
+X<%{^CAPTURE_ALL}>
=item %-
-X<%-> X<%LAST_MATCH_START>
+X<%->
Similar to C<%+>, this variable allows access to the named capture groups
in the last successful match in the currently active dynamic scope. To
@@ -1044,7 +1202,9 @@ Here's an example:
my $ary = $-{$bufname};
foreach my $idx (0..$#$ary) {
print "\$-{$bufname}[$idx] : ",
- (defined($ary->[$idx]) ? "'$ary->[$idx]'" : "undef"),
+ (defined($ary->[$idx])
+ ? "'$ary->[$idx]'"
+ : "undef"),
"\n";
}
}
@@ -1052,10 +1212,10 @@ Here's an example:
would print out:
- $-{A}[0] : '1'
- $-{A}[1] : '3'
- $-{B}[0] : '2'
- $-{B}[1] : '4'
+ $-{A}[0] : '1'
+ $-{A}[1] : '3'
+ $-{B}[0] : '2'
+ $-{B}[1] : '4'
The keys of the C<%-> hash correspond to all buffer names found in
the regular expression.
@@ -1069,7 +1229,8 @@ iterative access to them via C may have unpredictable results.
Likewise, if the last successful match changes, then the results may be
surprising.
-This variable was added in Perl 5.10
+This variable was added in Perl v5.10.0. The C<%{^CAPTURE_ALL}> alias was
+added in 5.25.7.
This variable is read-only and dynamically-scoped.
@@ -1089,7 +1250,7 @@ X<${^RE_DEBUG_FLAGS}>
The current value of the regex debugging flags. Set to 0 for no debug output
even when the C module is loaded. See L for details.
-This variable was added in Perl 5.10.
+This variable was added in Perl v5.10.0.
=item ${^RE_TRIE_MAXBUF}
X<${^RE_TRIE_MAXBUF}>
@@ -1103,7 +1264,7 @@ be as conservative of memory as possible but still occur, and set it to a
negative value to prevent the optimisation and conserve the most memory.
Under normal situations this variable should be of no interest to you.
-This variable was added in Perl 5.10.
+This variable was added in Perl v5.10.0.
=back
@@ -1115,15 +1276,15 @@ although this is less efficient than using the regular built-in
variables. (Summary lines below for this contain the word HANDLE.)
First you must say
- use IO::Handle;
+ use IO::Handle;
after which you may use either
- method HANDLE EXPR
+ method HANDLE EXPR
or more safely,
- HANDLE->method(EXPR)
+ HANDLE->method(EXPR)
Each method returns the old value of the C attribute. The
methods each take an optional EXPR, which, if supplied, specifies the
@@ -1145,17 +1306,17 @@ the change may affect other modules which rely on the default values
of the special variables that you have changed. This is one of the
correct ways to read the whole file at once:
- open my $fh, "<", "foo" or die $!;
- local $/; # enable localized slurp mode
- my $content = <$fh>;
- close $fh;
+ open my $fh, "<", "foo" or die $!;
+ local $/; # enable localized slurp mode
+ my $content = <$fh>;
+ close $fh;
But the following code is quite bad:
- open my $fh, "<", "foo" or die $!;
- undef $/; # enable slurp mode
- my $content = <$fh>;
- close $fh;
+ open my $fh, "<", "foo" or die $!;
+ undef $/; # enable slurp mode
+ my $content = <$fh>;
+ close $fh;
since some other module, may want to read data from some file in the
default "line mode", so if the code we have just presented has been
@@ -1167,26 +1328,26 @@ change affects the shortest scope possible. So unless you are already
inside some short C<{}> block, you should create one yourself. For
example:
- my $content = '';
- open my $fh, "<", "foo" or die $!;
- {
- local $/;
- $content = <$fh>;
- }
- close $fh;
+ my $content = '';
+ open my $fh, "<", "foo" or die $!;
+ {
+ local $/;
+ $content = <$fh>;
+ }
+ close $fh;
Here is an example of how your own code can go broken:
- for ( 1..3 ){
- $\ = "\r\n";
- nasty_break();
- print "$_";
- }
+ for ( 1..3 ){
+ $\ = "\r\n";
+ nasty_break();
+ print "$_";
+ }
- sub nasty_break {
+ sub nasty_break {
$\ = "\f";
# do something with $_
- }
+ }
You probably expect this code to print the equivalent of
@@ -1201,7 +1362,7 @@ first. The value you set in C is still there when you
return. The fix is to add C so the value doesn't leak out of
C:
- local $\ = "\f";
+ local $\ = "\f";
It's easy to notice the problem in such a short example, but in more
complicated code you are looking for trouble if you don't localize
@@ -1242,7 +1403,7 @@ when doing edit-in-place processing with B<-i>. Useful when you have
to do a lot of inserting and don't want to keep modifying C<$_>. See
L for the B<-i> switch.
-=item Handle->output_field_separator( EXPR )
+=item IO::Handle->output_field_separator( EXPR )
=item $OUTPUT_FIELD_SEPARATOR
@@ -1254,6 +1415,9 @@ X<$,> X<$OFS> X<$OUTPUT_FIELD_SEPARATOR>
The output field separator for the print operator. If defined, this
value is printed between each of print's arguments. Default is C.
+You cannot call C on a handle, only as a
+static method. See L.
+
Mnemonic: what is printed when there is a "," in your print statement.
=item HANDLE->input_line_number( EXPR )
@@ -1291,7 +1455,7 @@ which handle you last accessed.
Mnemonic: many programs use "." to mean the current line number.
-=item HANDLE->input_record_separator( EXPR )
+=item IO::Handle->input_record_separator( EXPR )
=item $INPUT_RECORD_SEPARATOR
@@ -1322,31 +1486,37 @@ be better for something. :-)
Setting C<$/> to a reference to an integer, scalar containing an
integer, or scalar that's convertible to an integer will attempt to
read records instead of lines, with the maximum record size being the
-referenced integer. So this:
+referenced integer number of characters. So this:
local $/ = \32768; # or \"32768", or \$var_containing_32768
open my $fh, "<", $myfile or die $!;
local $_ = <$fh>;
-will read a record of no more than 32768 bytes from FILE. If you're
+will read a record of no more than 32768 characters from $fh. If you're
not reading from a record-oriented file (or your OS doesn't have
record-oriented files), then you'll likely get a full chunk of data
with every read. If a record is larger than the record size you've
set, you'll get the record back in pieces. Trying to set the record
-size to zero or less will cause reading in the (rest of the) whole file.
+size to zero or less is deprecated and will cause $/ to have the value
+of "undef", which will cause reading in the (rest of the) whole file.
+
+As of 5.19.9 setting C<$/> to any other form of reference will throw a
+fatal exception. This is in preparation for supporting new ways to set
+C<$/> in the future.
+
+On VMS only, record reads bypass PerlIO layers and any associated
+buffering, so you must not mix record and non-record reads on the
+same filehandle. Record mode mixes with line mode only when the
+same buffering layer is in use for both modes.
-On VMS, record reads are done with the equivalent of C,
-so it's best not to mix record and non-record reads on the same
-file. (This is unlikely to be a problem, because any file you'd
-want to read in record mode is probably unusable in line mode.)
-Non-VMS systems do normal I/O, so it's safe to mix record and
-non-record reads of a file.
+You cannot call C on a handle, only as a
+static method. See L.
-See also L. Also see L$.>.
+See also L. Also see L$.>.
Mnemonic: / delimits line boundaries when quoting poetry.
-=item Handle->output_record_separator( EXPR )
+=item IO::Handle->output_record_separator( EXPR )
=item $OUTPUT_RECORD_SEPARATOR
@@ -1358,6 +1528,9 @@ X<$\> X<$ORS> X<$OUTPUT_RECORD_SEPARATOR>
The output record separator for the print operator. If defined, this
value is printed after the last of print's arguments. Default is C.
+You cannot call C on a handle, only as a
+static method. See L.
+
Mnemonic: you set C<$\> instead of adding "\n" at the end of the print.
Also, it's just like C<$/>, but it's what you get "back" from Perl.
@@ -1382,6 +1555,17 @@ how to select the output channel. See also L.
Mnemonic: when you want your pipes to be piping hot.
+=item ${^LAST_FH}
+X<${^LAST_FH}>
+
+This read-only variable contains a reference to the last-read filehandle.
+This is set by C<< >>, C, C, C and C.
+This is the same handle that C<$.> and C and C without arguments
+use. It is also the handle used when Perl appends ", line 1" to
+an error or warning message.
+
+This variable was added in Perl v5.18.0.
+
=back
=head3 Variables related to formats
@@ -1404,7 +1588,7 @@ of C<$^A> and empties. So you never really see the contents of C<$^A>
unless you call C yourself and then look at it. See
L and L.
-=item HANDLE->format_formfeed(EXPR)
+=item IO::Handle->format_formfeed(EXPR)
=item $FORMAT_FORMFEED
@@ -1413,6 +1597,9 @@ X<$^L> X<$FORMAT_FORMFEED>
What formats output as a form feed. The default is C<\f>.
+You cannot call C on a handle, only as a static
+method. See L.
+
=item HANDLE->format_page_number(EXPR)
=item $FORMAT_PAGE_NUMBER
@@ -1436,7 +1623,7 @@ channel.
Mnemonic: lines_on_page - lines_printed.
-=item Handle->format_line_break_characters EXPR
+=item IO::Handle->format_line_break_characters EXPR
=item $FORMAT_LINE_BREAK_CHARACTERS
@@ -1447,6 +1634,9 @@ The current set of characters after which a string may be broken to
fill continuation fields (starting with C<^>) in a format. The default is
S<" \n-">, to break on a space, newline, or a hyphen.
+You cannot call C on a handle, only as
+a static method. See L.
+
Mnemonic: a "colon" in poetry is a part of a line.
=item HANDLE->format_lines_per_page(EXPR)
@@ -1507,11 +1697,11 @@ following Perl expression, which uses a single-quoted string. After
execution of this statement, perl may have set all four special error
variables:
- eval q{
- open my $pipe, "/cdrom/install |" or die $!;
- my @res = <$pipe>;
- close $pipe or die "bad pipe: $?, $!";
- };
+ eval q{
+ open my $pipe, "/cdrom/install |" or die $!;
+ my @res = <$pipe>;
+ close $pipe or die "bad pipe: $?, $!";
+ };
When perl executes the C expression, it translates the
C, C<< >>, and C calls in the C run-time library
@@ -1528,12 +1718,12 @@ Under a few operating systems, C<$^E> may contain a more verbose error
indicator, such as in this case, "CDROM tray not closed." Systems that
do not support extended error messages leave C<$^E> the same as C<$!>.
-Finally, C<$?> may be set to non-0 value if the external program
+Finally, C<$?> may be set to a non-0 value if the external program
F fails. The upper eight bits reflect specific error
conditions encountered by the program (the program's C value).
The lower eight bits reflect mode of failure, like signal death and
core dump information. See L for details. In contrast to
-C<$!> and C<$^E>, which are set only if error condition is detected,
+C<$!> and C<$^E>, which are set only if an error condition is detected,
the variable C<$?> is set on each C or pipe C,
overwriting the old value. This is more like C<$@>, which on every
C is always set on failure and cleared on success.
@@ -1555,7 +1745,7 @@ WSTOPSIG and WIFCONTINUED functions provided by the L module.
Under VMS this reflects the actual VMS exit status; i.e. it is the
same as C<$?> when the pragma C is in effect.
-This variable was added in Perl 5.8.9.
+This variable was added in Perl v5.10.0.
=item $EXTENDED_OS_ERROR
@@ -1563,7 +1753,7 @@ This variable was added in Perl 5.8.9.
X<$^E> X<$EXTENDED_OS_ERROR>
Error information specific to the current operating system. At the
-moment, this differs from C<$!> under only VMS, OS/2, and Win32 (and
+moment, this differs from C> under only VMS, OS/2, and Win32 (and
for MacPerl). On all other platforms, C<$^E> is always just the same
as C<$!>.
@@ -1581,7 +1771,7 @@ from within the Win32 API. Most Win32-specific code will report errors
via C<$^E>. ANSI C and Unix-like calls set C and so most
portable Perl code will report errors via C<$!>.
-Caveats mentioned in the description of C<$!> generally apply to
+Caveats mentioned in the description of C> generally apply to
C<$^E>, also.
This variable was added in Perl 5.003.
@@ -1596,14 +1786,18 @@ X<$^S> X<$EXCEPTIONS_BEING_CAUGHT>
Current state of the interpreter.
$^S State
- --------- -------------------
- undef Parsing module/eval
+ --------- -------------------------------------
+ undef Parsing module, eval, or main program
true (1) Executing an eval
false (0) Otherwise
The first state may happen in C<$SIG{__DIE__}> and C<$SIG{__WARN__}>
handlers.
+The English name $EXCEPTIONS_BEING_CAUGHT is slightly misleading, because
+the C value does not indicate whether exceptions are being caught,
+since compilation of the main program does not catch exceptions.
+
This variable was added in Perl 5.004.
=item $WARNING
@@ -1622,9 +1816,11 @@ Mnemonic: related to the B<-w> switch.
X<${^WARNING_BITS}>
The current set of warning checks enabled by the C pragma.
-See the documentation of C for more details.
+It has the same scoping as the C<$^H> and C<%^H> variables. The exact
+values are considered internal to the L pragma and may change
+between versions of Perl.
-This variable was added in Perl 5.10.
+This variable was added in Perl v5.6.0.
=item $OS_ERROR
@@ -1675,10 +1871,12 @@ Each element of C<%!> has a true value only if C<$!> is set to that
value. For example, C<$!{ENOENT}> is true if and only if the current
value of C<$!> is C; that is, if the most recent error was "No
such file or directory" (or its moral equivalent: not all operating
-systems give that exact error, and certainly not all languages). To
-check if a particular key is meaningful on your system, use C; for a list of legal keys, use C. See L
-for more information, and also see L$!>.
+systems give that exact error, and certainly not all languages). The
+specific true value is not guaranteed, but in the past has generally
+been the numeric value of C<$!>. To check if a particular key is
+meaningful on your system, use C; for a list of legal
+keys, use C. See L for more information, and also see
+L$!>.
This variable was added in Perl 5.005.
@@ -1720,17 +1918,18 @@ Mnemonic: similar to B and B.
=item $@
X<$@> X<$EVAL_ERROR>
-The Perl syntax error message from the
-last C operator. If C<$@> is
-the null string, the last C parsed and executed correctly
-(although the operations you invoked may have failed in the normal
-fashion).
+The Perl error from the last C operator, i.e. the last exception that
+was caught. For C, this is either a runtime error message or the
+string or reference C was called with. The C form also
+catches syntax errors and other compile time exceptions.
+
+If no error occurs, C sets C<$@> to the empty string.
Warning messages are not collected in this variable. You can, however,
set up a routine to process warnings by setting C<$SIG{__WARN__}> as
described in L%SIG>.
-Mnemonic: Where was the syntax error "at"?
+Mnemonic: Where was the error "at"?
=back
@@ -1751,7 +1950,7 @@ when being compiled, such as for example to C at compile
time rather than normal, deferred loading. Setting
C<$^C = 1> is similar to calling C.
-This variable was added in Perl 5.6.
+This variable was added in Perl v5.6.0.
=item $DEBUGGING
@@ -1759,20 +1958,42 @@ This variable was added in Perl 5.6.
X<$^D> X<$DEBUGGING>
The current value of the debugging flags. May be read or set. Like its
-command-line equivalent, you can use numeric or symbolic values, eg
-C<$^D = 10> or C<$^D = "st">.
+LI>, you can use numeric
+or symbolic values, e.g. C<$^D = 10> or C<$^D = "st">. See
+LI>. The contents of this variable also affects the
+debugger operation. See L.
Mnemonic: value of B<-D> switch.
=item ${^ENCODING}
X<${^ENCODING}>
-The I