X-Git-Url: https://perl5.git.perl.org/perl5.git/blobdiff_plain/443f6d0184e0648ec41d1125072fe0e461cb089b..314d39ceeccf6c9ed18a761b1261137e0e8bdc75:/pod/perlvar.pod diff --git a/pod/perlvar.pod b/pod/perlvar.pod index dd9bbaa..8a37014 100644 --- a/pod/perlvar.pod +++ b/pod/perlvar.pod @@ -177,6 +177,11 @@ test. Outside a C test, this will not happen. =back +As C<$_> is a global variable, this may lead in some cases to unwanted +side-effects. As of perl 5.9.1, you can now use a lexical version of +C<$_> by declaring it in a file or in a block with C. Moreover, +declaring C restores the global C<$_> in the current scope. + (Mnemonic: underline is understood in certain operations.) =back @@ -189,10 +194,9 @@ test. Outside a C test, this will not happen. Special package variables when using sort(), see L. Because of this specialness $a and $b don't need to be declared -(using local(), use vars, or our()) even when using the strict -vars pragma. Don't lexicalize them with C or C -if you want to be able to use them in the sort() comparison block -or function. +(using use vars, or our()) even when using the C pragma. +Don't lexicalize them with C or C if you want to be +able to use them in the sort() comparison block or function. =back @@ -294,26 +298,6 @@ past where $2 ends, and so on. You can use C<$#+> to determine how many subgroups were in the last successful match. See the examples given for the C<@-> variable. -=item $MULTILINE_MATCHING - -=item $* - -Set to a non-zero integer value to do multi-line matching within a -string, 0 (or undefined) to tell Perl that it can assume that strings -contain a single line, for the purpose of optimizing pattern matches. -Pattern matches on strings containing multiple newlines can produce -confusing results when C<$*> is 0 or undefined. Default is undefined. -(Mnemonic: * matches multiple things.) This variable influences the -interpretation of only C<^> and C<$>. A literal newline can be searched -for even when C<$* == 0>. - -Use of C<$*> is deprecated in modern Perl, supplanted by -the C and C modifiers on pattern matching. - -Assigning a non-numerical value to C<$*> triggers a warning (and makes -C<$*> act if C<$* == 0>), while assigning a numerical value to C<$*> -makes that an implicit C is applied on the value. - =item HANDLE->input_line_number(EXPR) =item $INPUT_LINE_NUMBER @@ -390,7 +374,8 @@ will read a record of no more than 32768 bytes from FILE. 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. +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. 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 @@ -427,12 +412,9 @@ for that. (Mnemonic: when you want your pipes to be piping hot.) =item $, -The output field separator for the print operator. Ordinarily the -print operator simply prints out its arguments without further -adornment. To get behavior more like B, set this variable as -you would set B's OFS variable to specify what is printed -between fields. (Mnemonic: what is printed when there is a "," in -your print statement.) +The output field separator for the print operator. If defined, this +value is printed between each of print's arguments. Default is C. +(Mnemonic: what is printed when there is a "," in your print statement.) =item IO::Handle->output_record_separator EXPR @@ -442,14 +424,10 @@ your print statement.) =item $\ -The output record separator for the print operator. Ordinarily the -print operator simply prints out its arguments as is, with no -trailing newline or other end-of-record string added. To get -behavior more like B, set this variable as you would set -B's ORS variable to specify what is printed at the end of the -print. (Mnemonic: you set C<$\> instead of adding "\n" at the -end of the print. Also, it's just like C<$/>, but it's what you -get "back" from Perl.) +The output record separator for the print operator. If defined, this +value is printed after the last of print's arguments. Default is C. +(Mnemonic: you set C<$\> 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.) =item $LIST_SEPARATOR @@ -491,20 +469,6 @@ taken for something more important.) Consider using "real" multidimensional arrays as described in L. -=item $OFMT - -=item $# - -The output format for printed numbers. This variable is a half-hearted -attempt to emulate B's OFMT variable. There are times, however, -when B and Perl have differing notions of what counts as -numeric. The initial value is "%.Ig", where I is the value -of the macro DBL_DIG from your system's F. This is different from -B's default OFMT setting of "%.6g", so you need to set C<$#> -explicitly to get B's value. (Mnemonic: # is the number sign.) - -Use of C<$#> is deprecated. - =item HANDLE->format_page_number(EXPR) =item $FORMAT_PAGE_NUMBER @@ -546,9 +510,9 @@ C<$-[>IC<]> is the offset of the start of the substring matched by 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<], -$+[>IC<] - $-[>IC<]> if C<$-[>IC<]> is defined, and $+ coincides with -C. One can use C<$#-> to find the last +$+[0] - $-[0]>. Similarly, $I coincides with C if C<$-[n]> is defined, and $+ coincides with +C. One can use C<$#-> to find the last matched subgroup in the last successful match. Contrast with C<$#+>, the number of subgroups in the regular expression. Compare with C<@+>. @@ -574,7 +538,7 @@ After a match against some variable $var: =item C<$2> is the same as C -=item C<$3> is the same as C +=item C<$3> is the same as C =back @@ -635,7 +599,7 @@ L. The status returned by the last pipe close, backtick (C<``>) command, successful call to wait() or waitpid(), or from the system() operator. This is just the 16-bit status word returned by the -wait() system call (or else is made up to look like it). Thus, the +traditional Unix wait() system call (or else is made up to look like it). Thus, the exit value of the subprocess is really (C<<< $? >> 8 >>>), and C<$? & 127> gives which signal, if any, the process died from, and C<$? & 128> reports whether there was a core dump. (Mnemonic: @@ -661,6 +625,17 @@ status; see L for details. Also see L. +=item ${^CHILD_ERROR_NATIVE} + +The native status returned by the last pipe close, backtick (C<``>) +command, successful call to wait() or waitpid(), or from the system() +operator. On POSIX-like systems this value can be decoded with the +WIFEXITED, WEXITSTATUS, WIFSIGNALED, WTERMSIG, WIFSTOPPED, 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 $? when the pragma C is in effect. + =item ${^ENCODING} The I to the Encode object that is used to convert @@ -695,7 +670,7 @@ In the above I stands for anything: zero, non-zero, C. A successful system or library call does B set the variable to zero. -If used an a string, yields the corresponding system error string. +If used as a string, yields the corresponding system error string. You can assign a number to C<$!> to set I if, for instance, you want C<"$!"> to return the string for error I, or you want to set the exit value for the die() operator. (Mnemonic: What just @@ -769,6 +744,12 @@ The process number of the Perl running this script. You should consider this variable read-only, although it will be altered across fork() calls. (Mnemonic: same as shells.) +Note for Linux users: on Linux, the C functions C and +C return different values from different threads. In order to +be portable, this behavior is not reflected by C<$$>, whose value remains +consistent across threads. If you want to call the underlying C, +you may use the CPAN module C. + =item $REAL_USER_ID =item $UID @@ -777,7 +758,9 @@ across fork() calls. (Mnemonic: same as shells.) The real uid of this process. (Mnemonic: it's the uid you came I, if you're running setuid.) You can change both the real uid and -the effective uid at the same time by using POSIX::setuid(). +the effective uid at the same time by using POSIX::setuid(). Since +changes to $< require a system call, check $! after a change attempt to +detect any possible errors. =item $EFFECTIVE_USER_ID @@ -791,7 +774,8 @@ The effective uid of this process. Example: ($<,$>) = ($>,$<); # swap real and effective uid You can change both the effective uid and the real uid at the same -time by using POSIX::setuid(). +time by using POSIX::setuid(). Changes to $> require a check to $! +to detect any possible errors after an attempted change. (Mnemonic: it's the uid you went I, if you're running setuid.) C<< $< >> and C<< $> >> can be swapped only on machines @@ -814,7 +798,8 @@ set the real gid. So the value given by C<$(> should I be assigned back to C<$(> without being forced numeric, such as by adding zero. You can change both the real gid and the effective gid at the same -time by using POSIX::setgid(). +time by using POSIX::setgid(). Changes to $( require a check to $! +to detect any possible errors after an attempted change. (Mnemonic: parentheses are used to I things. The real gid is the group you I, if you're running setgid.) @@ -840,6 +825,8 @@ list, say C< $) = "5 5" >. You can change both the effective gid and the real gid at the same time by using POSIX::setgid() (use only a single numeric argument). +Changes to $) require a check to $! to detect any possible errors +after an attempted change. (Mnemonic: parentheses are used to I things. The effective gid is the group that's I for you, if you're running setgid.) @@ -852,16 +839,36 @@ and C<$)> can be swapped only on machines supporting setregid(). =item $0 -Contains the name of the program being executed. On some operating -systems assigning to C<$0> modifies the argument area that the B -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 and B.) +Contains the name of the program being executed. + +On some (read: not all) operating systems assigning to C<$0> modifies +the argument area that the C program sees. On some platforms you +may have to use special C options or a different C to see the +changes. Modifying the $0 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 and B.) + +Note that there are platform specific limitations on the maximum +length of C<$0>. In the most extreme case it may be limited to the +space occupied by the original C<$0>. + +In some platforms there may be arbitrary amount of padding, for +example space characters, after the modified name as shown by C. +In some platforms this padding may extend all the way to the original +length of the argument area, no matter what you do (this is the case +for example with Linux 2.2). Note for BSD users: setting C<$0> does not completely remove "perl" -from the ps(1) output. For example, setting C<$0> to C<"foobar"> will -result in C<"perl: foobar (perl)">. This is an operating system -feature. +from the ps(1) output. For example, setting C<$0> to C<"foobar"> may +result in C<"perl: foobar (perl)"> (whether both the C<"perl: "> prefix +and the " (perl)" suffix are shown depends on your exact BSD variant +and version). This is an operating system feature, Perl cannot help it. + +In multithreaded scripts Perl coordinates the threads so that any +thread may modify its copy of the C<$0> and the change becomes visible +to ps(1) (assuming the operating system plays along). Note that +the view of C<$0> the other threads have will not change since they +have their own copies of it. =item $[ @@ -873,8 +880,14 @@ subscripting and when evaluating the index() and substr() functions. As of release 5 of Perl, assignment to C<$[> is treated as a compiler directive, and cannot influence the behavior of any other file. +(That's why you can only assign compile-time constants to it.) Its use is highly discouraged. +Note that, unlike other compile-time directives (such as L), +assignment to C<$[> can be seen from outer lexical scopes in the same file. +However, you can use local() on it to strictly bind its value to a +lexical block. + =item $] The version + patchlevel / 1000 of the Perl interpreter. This variable @@ -906,7 +919,23 @@ C<$^C = 1> is similar to calling C. =item $^D The current value of the debugging flags. (Mnemonic: value of B<-D> -switch.) +switch.) May be read or set. Like its command-line equivalent, you can use +numeric or symbolic values, eg C<$^D = 10> or C<$^D = "st">. + +=item ${^RE_DEBUG_FLAGS} + +The current value of the regex debugging flags. Set to 0 for no debug output +even when the re 'debug' module is loaded. See L for details. + +=item ${^RE_TRIE_MAXBUF} + +Controls how certain regex optimisations are applied and how much memory they +utilize. This value by default is 65536 which corresponds to a 512kB temporary +cache. Set this to a higher value to trade memory for speed when matching +large alternations. Set it to a lower value if you want the optimisations to +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. =item $SYSTEM_FD_MAX @@ -966,11 +995,8 @@ version of the same lexical pragma: =item %^H -WARNING: This variable is strictly for internal use only. Its availability, -behavior, and contents are subject to change without notice. - The %^H hash provides the same scoping semantic as $^H. This makes it -useful for implementation of lexically scoped pragmas. +useful for implementation of lexically scoped pragmas. See L. =item $INPLACE_EDIT @@ -984,15 +1010,16 @@ inplace editing. (Mnemonic: value of B<-i> switch.) By default, running out of memory is an untrappable, fatal error. However, if suitably built, Perl can use the contents of C<$^M> as an emergency memory pool after die()ing. Suppose that your Perl -were compiled with -DPERL_EMERGENCY_SBRK and used Perl's malloc. +were compiled with C<-DPERL_EMERGENCY_SBRK> and used Perl's malloc. Then $^M = 'a' x (1 << 16); would allocate a 64K buffer for use in an emergency. See the F file in the Perl distribution for information on how to -enable this option. To discourage casual use of this advanced -feature, there is no L long name for this variable. +add custom C compilation flags when compiling perl. To discourage casual +use of this advanced feature, there is no L long name for +this variable. =item $OSNAME @@ -1004,16 +1031,16 @@ is identical to C<$Config{'osname'}>. See also L and the B<-V> command-line switch documented in L. In Windows platforms, $^O is not very helpful: since it is always -C, it doesn't tell the difference between 95/98/ME/NT/2000/XP/CE. -Use Win32::GetOSVersion() (see L) and other means (like for -example the presence/absence of some files) to distinguish between -the variants. +C, it doesn't tell the difference between +95/98/ME/NT/2000/XP/CE/.NET. Use Win32::GetOSName() or +Win32::GetOSVersion() (see L and L) to distinguish +between the variants. =item ${^OPEN} An internal variable used by PerlIO. A string in two parts, separated -by a C<\0> byte, the first part is the input disciplines, the second -part is the output disciplines. +by a C<\0> byte, the first part describes the input layers, the second +part describes the output layers. =item $PERLDB @@ -1065,6 +1092,10 @@ Provide informative "file" names for evals based on the place they were compiled Provide informative names to anonymous subroutines based on the place they were compiled. +=item 0x400 + +Debug assertion subroutines enter/exit. + =back Some bits may be relevant at compile-time only, some at @@ -1081,9 +1112,15 @@ regular expression assertion (see L). May be written to. =item $^S -Current state of the interpreter. Undefined if parsing of the current -module/eval is not finished (may happen in $SIG{__DIE__} and -$SIG{__WARN__} handlers). True if inside an eval(), otherwise false. +Current state of the interpreter. + + $^S State + --------- ------------------- + undef Parsing module/eval + true (1) Executing an eval + false (0) Otherwise + +The first state may happen in $SIG{__DIE__} and $SIG{__WARN__} handlers. =item $BASETIME @@ -1095,8 +1132,29 @@ and B<-C> filetests are based on this value. =item ${^TAINT} -Reflects if taint mode is on or off (i.e. if the program was run with -B<-T> or not). True for on, false for off. +Reflects if taint mode is on or off. 1 for on (the program was run with +B<-T>), 0 for off, -1 when only taint warnings are enabled (i.e. with +B<-t> or B<-TU>). This variable is read-only. + +=item ${^UNICODE} + +Reflects certain Unicode settings of Perl. See L +documentation for the C<-C> switch for more information about +the possible values. This variable is set during Perl startup +and is thereafter read-only. + +=item ${^UTF8CACHE} + +This variable controls the state of the internal UTF-8 offset caching code. +1 for on (the default), 0 for off, -1 to debug the caching code by checking +all its results against linear scans, and panicking on any discrepancy. + +=item ${^UTF8LOCALE} + +This variable indicates whether an UTF-8 locale was detected by perl at +startup. This information is used by perl when it's in +adjust-utf8ness-to-locale mode (as when run with the C<-CL> command-line +switch); see L for more info on this. =item $PERL_VERSION @@ -1108,11 +1166,14 @@ it equals C and will return true for C<$^V eq v5.6.0>. Note that the characters in this string value can potentially be in Unicode range. +This variable first appeared in perl 5.6.0; earlier versions of perl will +see an undefined value. + This can be used to determine whether the Perl interpreter executing a script is in the right range of versions. (Mnemonic: use ^V for Version Control.) Example: - warn "No \"our\" declarations!\n" if $^V and $^V lt v5.6.0; + warn "Hashes not randomized!\n" if !$^V or $^V lt v5.8.1 To convert C<$^V> into its string representation use sprintf()'s C<"%vd"> conversion: @@ -1137,27 +1198,25 @@ related to the B<-w> switch.) See also L. The current set of warning checks enabled by the C pragma. See the documentation of C for more details. -=item ${^WIDE_SYSTEM_CALLS} +=item ${^WIN32_SLOPPY_STAT} -Global flag that enables system calls made by Perl to use wide character -APIs native to the system, if available. This is currently only implemented -on the Windows platform. +If this variable is set to a true value, then stat() on Windows will +not try to open the file. This means that the link count cannot be +determined and file attributes may be out of date if additional +hardlinks to the file exist. On the other hand, not opening the file +is considerably faster, especially for files on network drives. -This can also be enabled from the command line using the C<-C> switch. - -The initial value is typically C<0> for compatibility with Perl versions -earlier than 5.6, but may be automatically set to C<1> by Perl if the system -provides a user-settable default (e.g., C<$ENV{LC_CTYPE}>). - -The C pragma always overrides the effect of this flag in the current -lexical scope. See L. +This variable could be set in the F file to +configure the local Perl installation to use "sloppy" stat() by +default. See L for more information about site +customization. =item $EXECUTABLE_NAME =item $^X The name used to execute the current copy of Perl, from C's -C. +C or (where supported) F. Depending on the host operating system, the value of $^X may be a relative or absolute pathname of the perl program file, or may @@ -1182,7 +1241,7 @@ executable files do not require use of the suffix when invoking a command. To convert the value of $^X to a path name, use the following statements: -# Build up a set of file names (not command names). + # Build up a set of file names (not command names). use Config; $this_perl = $^X; if ($^O ne 'VMS') @@ -1225,6 +1284,13 @@ the script. C<$#ARGV> is generally the number of arguments minus one, because C<$ARGV[0]> is the first argument, I the program's command name itself. See C<$0> for the command name. +=item ARGVOUT + +The special filehandle that points to the currently open output file +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 $_. See +L for the B<-i> switch. + =item @F The array @F contains the fields of each line read in when autosplit @@ -1251,6 +1317,8 @@ You can also insert hooks into the file inclusion system by putting Perl code directly into @INC. Those hooks may be subroutine references, array references or blessed objects. See L for details. +=item @ARG + =item @_ Within a subroutine the array @_ contains the parameters passed to that @@ -1313,20 +1381,11 @@ Be sure not to use a bareword as the name of a signal handler, lest you inadvertently call it. If your system has the sigaction() function then signal handlers are -installed using it. This means you get reliable signal handling. If -your system has the SA_RESTART flag it is used when signals handlers are -installed. This means that system calls for which restarting is supported -continue rather than returning when a signal arrives. If you want your -system calls to be interrupted by signal delivery then do something like -this: - - use POSIX ':signal_h'; - - my $alarm = 0; - sigaction SIGALRM, new POSIX::SigAction sub { $alarm = 1 } - or die "Error setting SIGALRM handler: $!\n"; +installed using it. This means you get reliable signal handling. -See L. +The default delivery policy of signals changed in Perl 5.8.0 from +immediate (also known as "unsafe") to deferred, also known as +"safe signals". See L for more information. Certain internal hooks can be also set using the %SIG hash. The routine indicated by C<$SIG{__WARN__}> is called when a warning message is @@ -1401,7 +1460,7 @@ C<$@> is set if the string to be C-ed did not compile (this may happen if C or C were imported with bad prototypes), or if Perl code executed during evaluation die()d . In these cases the value of $@ is the compile error, or the argument to C -(which will interpolate C<$!> and C<$?>!). (See also L, +(which will interpolate C<$!> and C<$?>). (See also L, though.) When the eval() expression above is executed, open(), C<< >>, @@ -1460,18 +1519,19 @@ used safely in programs. C<$^_> itself, however, I reserved. Perl identifiers that begin with digits, control characters, or punctuation characters are exempt from the effects of the C -declaration and are always forced to be in package C
. A few -other names are also exempt: +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 + ARGVOUT _ SIG In particular, the new special C<${^_XYZ}> variables are always taken to be in package C
, regardless of any C declarations -presently in scope. +presently in scope. =head1 BUGS