diff options
Diffstat (limited to 'pod/perlvar.pod')
| -rw-r--r-- | pod/perlvar.pod | 76 |
1 files changed, 34 insertions, 42 deletions
diff --git a/pod/perlvar.pod b/pod/perlvar.pod index 1406858331..b569465d15 100644 --- a/pod/perlvar.pod +++ b/pod/perlvar.pod @@ -52,7 +52,7 @@ The default input and pattern-searching space. The following pairs are equivalent: while (<>) {...} # equivalent in only while! - while ($_ = <>) {...} + while (defined($_ = <>)) {...} /^Subject:/ $_ =~ /^Subject:/ @@ -63,7 +63,7 @@ equivalent: chop chop($_) -Here are the places where Perl will assume $_ even if you +Here are the places where Perl will assume $_ even if you don't use it: =over 3 @@ -83,16 +83,16 @@ Various list functions like print() and unlink(). The pattern matching operations C<m//>, C<s///>, and C<tr///> when used without an C<=~> operator. -=item * +=item * The default iterator variable in a C<foreach> loop if no other variable is supplied. -=item * +=item * The implicit iterator variable in the grep() and map() functions. -=item * +=item * The default place to put an input record when a C<E<lt>FHE<gt>> operation's result is tested by itself as the sole criterion of a C<while> @@ -108,7 +108,7 @@ test. Note that outside of a C<while> test, this will not happen. =item $E<lt>I<digit>E<gt> -Contains the sub-pattern from the corresponding set of parentheses in +Contains the subpattern from the corresponding set of parentheses in the last pattern matched, not counting patterns matched in nested blocks that have been exited already. (Mnemonic: like \digit.) These variables are all read-only. @@ -162,7 +162,7 @@ This variable is read-only. =item $* -Set to 1 to do multi-line matching within a string, 0 to tell Perl +Set to 1 to do multiline matching within a string, 0 to tell Perl that it can assume that strings contain a single line, for the purpose of optimizing pattern matches. Pattern matches on strings containing multiple newlines can produce confusing results when "C<$*>" is 0. Default @@ -199,15 +199,15 @@ number.) The input record separator, newline by default. Works like B<awk>'s RS variable, including treating empty lines as delimiters if set to the -null string. (Note: An empty line cannot contain any spaces or -tabs.) You may set it to a multicharacter string to match a -multi-character delimiter. Note that setting it to C<"\n\n"> means -something slightly different than setting it to C<"">, if the file -contains consecutive empty lines. Setting it to C<""> will treat two -or more consecutive empty lines as a single empty line. Setting it to -C<"\n\n"> will blindly assume that the next input character belongs to -the next paragraph, even if it's a newline. (Mnemonic: / is used to -delimit line boundaries when quoting poetry.) +null string. (Note: An empty line cannot contain any spaces or tabs.) +You may set it to a multicharacter string to match a multicharacter +delimiter, or to C<undef> to read to end of file. Note that setting it +to C<"\n\n"> means something slightly different than setting it to +C<"">, if the file contains consecutive empty lines. Setting it to +C<""> will treat two or more consecutive empty lines as a single empty +line. Setting it to C<"\n\n"> will blindly assume that the next input +character belongs to the next paragraph, even if it's a newline. +(Mnemonic: / is used to delimit line boundaries when quoting poetry.) undef $/; $_ = <FH>; # whole file now here @@ -222,10 +222,10 @@ better for something :-) =item $| -If set to nonzero, forces a flush after every write or print on the +If set to nonzero, forces a flush right away and after every write or print on the currently selected output channel. Default is 0 (regardless of whether the channel is actually buffered by the system or not; C<$|> tells you -only whether you've asked Perl explicitly to flush after each write). +only whether you've asked Perl explicitly to flush after each write). Note that STDOUT will typically be line buffered if output is to the terminal and block buffered otherwise. Setting this variable is useful primarily when you are outputting to a pipe, such as when you are running @@ -279,7 +279,7 @@ is a space. (Mnemonic: obvious, I think.) =item $; -The subscript separator for multi-dimensional array emulation. If you +The subscript separator for multidimensional array emulation. If you refer to a hash element as $foo{$a,$b,$c} @@ -302,7 +302,7 @@ keys contain binary data there might not be any safe value for "C<$;>". semi-semicolon. Yeah, I know, it's pretty lame, but "C<$,>" is already taken for something more important.) -Consider using "real" multi-dimensional arrays. +Consider using "real" multidimensional arrays. =item $OFMT @@ -372,7 +372,7 @@ appended. (Mnemonic: points to top of page.) =item $: The current set of characters after which a string may be broken to -fill continuation fields (starting with ^) in a format. Default is +fill continuation fields (starting with ^) in a format. Default is S<" \n-">, to break on whitespace or hyphens. (Mnemonic: a "colon" in poetry is a part of a line.) @@ -399,7 +399,7 @@ L<perlfunc/formline()>. =item $? -The status returned by the last pipe close, back-tick (C<``>) command, +The status returned by the last pipe close, backtick (C<``>) command, or system() operator. Note that this is the status word returned by the wait() system call (or else is made up to look like it). Thus, the exit value of the subprocess is actually (C<$? E<gt>E<gt> 8>), and @@ -459,7 +459,7 @@ the syntax error "at"?) Note that warning messages are not collected in this variable. You can, however, set up a routine to process warnings by setting C<$SIG{__WARN__}> -below. +as described below. =item $PROCESS_ID @@ -531,7 +531,8 @@ multiple groups. =item $0 Contains the name of the file containing the Perl script being -executed. Assigning to "C<$0>" modifies the argument area that the ps(1) +executed. On some operating systems +assigning to "C<$0>" modifies the argument area that the ps(1) program sees. This is more useful as a way of indicating the current program state than it is for hiding the program you're running. (Mnemonic: same as B<sh> and B<ksh>.) @@ -552,24 +553,15 @@ discouraged. =item $] -The string printed out when you say C<perl -v>. -(This is currently I<BROKEN>). -It can be used to -determine at the beginning of a script whether the perl interpreter -executing the script is in the right range of versions. If used in a -numeric context, returns the version + patchlevel / 1000. Example: - - # see if getc is available - ($version,$patchlevel) = - $] =~ /(\d+\.\d+).*\nPatch level: (\d+)/; - print STDERR "(No filename completion available.)\n" - if $version * 1000 + $patchlevel < 2016; - -or, used numerically, +The version + patchlevel / 1000 of the Perl interpreter. This variable +can be used to determine whether the Perl interpreter executing a +script is in the right range of versions. (Mnemonic: Is this version +of perl in the right bracket?) Example: warn "No checksumming!\n" if $] < 3.019; -(Mnemonic: Is this version of perl in the right bracket?) +See also the documentation of C<use VERSION> and C<require VERSION> +for a convenient way to fail if the Perl interpreter is too old. =item $DEBUGGING @@ -704,7 +696,7 @@ the Perl script. Here are some other examples: $SIG{"PIPE"} = Plumber(); # oops, what did Plumber() return?? The one marked scary is problematic because it's a bareword, which means -sometimes it's a string representing the function, and sometimes it's +sometimes it's a string representing the function, and sometimes it's going to call the subroutine call right then and there! Best to be sure and quote it or take a reference to it. *Plumber works too. See L<perlsub>. @@ -749,9 +741,9 @@ By default, running out of memory it is not trappable. However, if compiled for this, Perl may use the contents of C<$^M> as an emergency pool after die()ing with this message. Suppose that your Perl were compiled with -DEMERGENCY_SBRK and used Perl's malloc. Then - + $^M = 'a' x (1<<16); - + would allocate a 64K buffer for use when in emergency. See the F<INSTALL> file for information on how to enable this option. As a disincentive to casual use of this advanced feature, there is no L<English> long name for |