long names in the current package. Some even have medium names,
generally borrowed from B<awk>.
+Due to an unfortunate accident of Perl's implementation, "C<use English>"
+imposes a considerable performance penalty on all regular expression
+matches in a program, regardless of whether they occur in the scope of
+"C<use English>". For that reason, saying "C<use English>" 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
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 $`
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 $'
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 $+
(Mnemonic: be positive and forward looking.)
This variable is read-only.
+=item @+
+
+$+[0] is the offset of the end of the last successfull match.
+C<$+[>I<n>C<]> is the offset of the end of the substring matched by
+I<n>-th subpattern, or undef if the subpattern did not match.
+
+Thus after a match against $_, $& coincides with C<substr $_, $-[0],
+$+[0] - $-[0]>. Similarly, C<$>I<n> coincides with C<substr $_, $-[>I<n>C<],
+$+[>I<n>C<] - $-[>I<n>C<]> if C<$-[>I<n>C<]> is defined, and $+ coincides with
+C<substr $_, $-[$#-], $+[$#-]>. 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<matched> subgroup. Compare with L<"@-">.
+
=item $MULTILINE_MATCHING
=item $*
The number of lines left on the page of the currently selected output
channel. (Mnemonic: lines_on_page - lines_printed.)
+=item @-
+
+$-[0] is the offset of the start of the last successfull match.
+C<$-[>I<n>C<]> is the offset of the start of the substring matched by
+I<n>-th subpattern, or undef if the subpattern did not match.
+
+Thus after a match against $_, $& coincides with C<substr $_, $-[0],
+$+[0] - $-[0]>. Similarly, C<$>I<n> coincides with C<substr $_, $-[>I<n>C<],
+$+[>I<n>C<] - $-[>I<n>C<]> if C<$-[>I<n>C<]> is defined, and $+ coincides with
+C<substr $_, $-[$#-], $+[$#-]>. 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
=item $FORMAT_NAME
actual VMS exit status, instead of the default emulation of POSIX
status.
+Also see L<Error Indicators>.
+
=item $OS_ERROR
=item $ERRNO
string for error I<n>, or you want to set the exit value for the die()
operator. (Mnemonic: What just went bang?)
+Also see L<Error Indicators>.
+
=item $EXTENDED_OS_ERROR
=item $^E
Caveats mentioned in the description of C<$!> generally apply to
C<$^E>, also. (Mnemonic: Extra error explanation.)
+Also see L<Error Indicators>.
+
=item $EVAL_ERROR
=item $@
however, set up a routine to process warnings by setting C<$SIG{__WARN__}>
as described below.
+Also see L<Error Indicators>.
+
=item $PROCESS_ID
=item $PID
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 $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<B::minus_c>.
+
=item $DEBUGGING
=item $^D
preserved even if the open() fails. (Ordinary file descriptors are
closed before the open() is attempted.) Note that the close-on-exec
status of a file descriptor will be decided according to the value of
-C<$^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
Note that some bits may be relevent at compile-time only, some at
run-time only. This is a new mechanism and the details may change.
+=item $^R
+
+The result of evaluation of the last successful L<perlre/C<(?{ code })>>
+regular expression assertion. (Excluding those used as switches.) May
+be written to.
+
=item $^S
Current state of the interpreter. Undefined if parsing of the current
The C<require> 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<ENV> 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:
$SIG{'INT'} = 'DEFAULT'; # restore default action
$SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT
+Using a value of C<'IGNORE'> usually has the effect of ignoring the
+signal, except for the C<CHLD> signal. See L<perlipc> for more about
+this special case.
+
The %SIG array contains values for only the signals actually set within
the Perl script. Here are some other examples:
additional info.
=back
+
+=head2 Error Indicators
+
+The variables L<$@>, L<$!>, L<$^E>, and L<$?> contain information about
+different types of error conditions that may appear during execution of
+Perl script. The variables are shown ordered by the "distance" between
+the subsystem which reported the error and the Perl process, and
+correspond to errors detected by the Perl interpreter, C library,
+operating system, or an external program, respectively.
+
+To illustrate the differences between these variables, consider the
+following Perl expression:
+
+ eval '
+ open PIPE, "/cdrom/install |";
+ @res = <PIPE>;
+ close PIPE or die "bad pipe: $?, $!";
+ ';
+
+After execution of this statement all 4 variables may have been set.
+
+$@ is set if the string to be C<eval>-ed did not compile (this may happen if
+C<open> or C<close> were imported with bad prototypes), or if Perl
+code executed during evaluation die()d (either implicitly, say,
+if C<open> was imported from module L<Fatal>, or the C<die> after
+C<close> was triggered). In these cases the value of $@ is the compile
+error, or C<Fatal> error (which will interpolate C<$!>!), or the argument
+to C<die> (which will interpolate C<$!> and C<$?>!).
+
+When the above expression is executed, open(), C<<PIPEE<gt>>, and C<close>
+are translated to C run-time library calls. $! is set if one of these
+calls fails. The value is a symbolic indicator chosen by the C run-time
+library, say C<No such file or directory>.
+
+On some systems the above C library calls are further translated
+to calls to the kernel. The kernel may have set more verbose error
+indicator that one of the handful of standard C errors. In such cases $^E
+contains this verbose error indicator, which may be, say, C<CDROM tray not
+closed>. On systems where C library calls are identical to system calls
+$^E is a duplicate of $!.
+
+Finally, $? may be set to non-C<0> value if the external program
+C</cdrom/install> fails. Upper bits of the particular value may reflect
+specific error conditions encountered by this program (this is
+program-dependent), lower-bits reflect mode of failure (segfault, completion,
+etc.). Note that in contrast to $@, $!, and $^E, which are set only
+if error condition is detected, the variable $? is set on each C<wait> or
+pipe C<close>, overwriting the old value.
+
+For more details, see the individual descriptions at L<$@>, L<$!>, L<$^E>,
+and L<$?>.
projects / p5sagit/p5-mst-13.2.git / blobdiff