X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlvar.pod;h=b9b0ce6c0a259b5c470f7d15c4be57ac21a16d80;hb=c8984b0bd19897e6e30588055ac0338326f20a34;hp=739dd55cd2bcb4438c2f3e301159f892f8530527;hpb=6cef1e77274f883a8b06f0546efeff6e6b8660d8;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlvar.pod b/pod/perlvar.pod index 739dd55..b9b0ce6 100644 --- a/pod/perlvar.pod +++ b/pod/perlvar.pod @@ -17,6 +17,15 @@ at the top of your program. This will alias all the short names to the long names in the current package. Some even have medium names, generally borrowed from B. +Due to an unfortunate accident of Perl's implementation, "C" +imposes a considerable performance penalty on all regular expression +matches in a program, regardless of whether they occur in the scope of +"C". For that reason, saying "C" in +libraries is strongly discouraged. See the Devel::SawAmpersand module +documentation from CPAN +(http://www.perl.com/CPAN/modules/by-module/Devel/Devel-SawAmpersand-0.10.readme) +for more information. + To go a step further, those variables that depend on the currently selected filehandle may instead (and preferably) be set by calling an object method on the FileHandle object. (Summary lines below for this @@ -127,6 +136,10 @@ The string matched by the last successful pattern match (not counting any matches hidden within a BLOCK or eval() enclosed by the current BLOCK). (Mnemonic: like & in some editors.) This variable is read-only. +The use of this variable anywhere in a program imposes a considerable +performance penalty on all regular expression matches. See the +Devel::SawAmpersand module from CPAN for more information. + =item $PREMATCH =item $` @@ -136,6 +149,10 @@ pattern match (not counting any matches hidden within a BLOCK or eval enclosed by the current BLOCK). (Mnemonic: C<`> often precedes a quoted string.) This variable is read-only. +The use of this variable anywhere in a program imposes a considerable +performance penalty on all regular expression matches. See the +Devel::SawAmpersand module from CPAN for more information. + =item $POSTMATCH =item $' @@ -151,6 +168,10 @@ string.) Example: This variable is read-only. +The use of this variable anywhere in a program imposes a considerable +performance penalty on all regular expression matches. See the +Devel::SawAmpersand module from CPAN for more information. + =item $LAST_PAREN_MATCH =item $+ @@ -168,13 +189,14 @@ This variable is read-only. $+[0] is the offset of the end of the last successfull match. C<$+[>IC<]> is the offset of the end of the substring matched by -I-th subpattern. +I-th subpattern, or undef if the subpattern did not match. Thus after a match against $_, $& coincides with C. Similarly, C<$>I coincides with CIC<], -$+[>I<0>C<]> if C<$-[>IC<]> is defined, and $+ conincides with -C. One can use C<$#+> to find the last -matched subgroup in the last successful match. Compare with L<"@-">. +$+[0] - $-[0]>. Similarly, C<$>I coincides with CIC<], +$+[>IC<] - $-[>IC<]> if C<$-[>IC<]> is defined, and $+ coincides with +C. One can use C<$#+> to find the number +of subgroups in the last successful match. Note the difference with +C<$#->, which is the last I subgroup. Compare with L<"@-">. =item $MULTILINE_MATCHING @@ -389,13 +411,15 @@ channel. (Mnemonic: lines_on_page - lines_printed.) $-[0] is the offset of the start of the last successfull match. C<$-[>IC<]> is the offset of the start of the substring matched by -I-th subpattern. +I-th subpattern, or undef if the subpattern did not match. Thus after a match against $_, $& coincides with C. Similarly, C<$>I coincides with CIC<], -$+[>I<0>C<]> if C<$-[>IC<]> is defined, and $+ conincides with -C. One can use C<$#-> to find the last -matched subgroup in the last successful match. Compare with L<"@+">. +$+[0] - $-[0]>. Similarly, C<$>I coincides with CIC<], +$+[>IC<] - $-[>IC<]> if C<$-[>IC<]> is defined, and $+ coincides with +C. One can use C<$#-> to find the last +matched subgroup in the last successful match. Note the difference with +C<$#+>, which is the number of subgroups in the regular expression. Compare +with L<"@+">. =item format_name HANDLE EXPR @@ -650,6 +674,15 @@ of perl in the right bracket?) Example: See also the documentation of C and C for a convenient way to fail if the Perl interpreter is too old. +=item $COMPILING + +=item $^C + +The current value of the flag associated with the B<-c> switch. Mainly +of use with B<-MO=...> to allow code to alter its behaviour when being compiled. +(For example to automatically AUTOLOADing at compile time rather than normal +deferred loading.) Setting C<$^C = 1> is similar to calling C. + =item $DEBUGGING =item $^D @@ -667,7 +700,7 @@ descriptors are not. Also, during an open(), system file descriptors are preserved even if the open() fails. (Ordinary file descriptors are closed before the open() is attempted.) Note that the close-on-exec status of a file descriptor will be decided according to the value of -C<$^F> at the time of the open, not the time of the exec. +C<$^F> when the open() or pipe() was called, not the time of the exec(). =item $^H @@ -812,12 +845,16 @@ specified, and the value is the location of the file actually found. The C command uses this array to determine whether a given file has already been included. -=item %ENV $ENV{expr} +=item %ENV + +=item $ENV{expr} The hash %ENV contains your current environment. Setting a value in C changes the environment for child processes. -=item %SIG $SIG{expr} +=item %SIG + +=item $SIG{expr} The hash %SIG is used to set signal handlers for various signals. Example: @@ -835,6 +872,10 @@ signals. Example: $SIG{'INT'} = 'DEFAULT'; # restore default action $SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT +Using a value of C<'IGNORE'> usually has the effect of ignoring the +signal, except for the C signal. See L for more about +this special case. + The %SIG array contains values for only the signals actually set within the Perl script. Here are some other examples: