B<perl> S<[ B<-sTtuUWX> ]>
S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]>
- S<[ B<-cw> ] [ B<-d>[:I<debugger>] ] [ B<-D>[I<number/list>] ]>
+ S<[ B<-cw> ] [ B<-d>[B<t>][:I<debugger>] ] [ B<-D>[I<number/list>] ]>
S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal/hexadecimal>] ]>
- S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ]>
- S<[ B<-P> ]>
+ S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ] [ B<-f> ]>
+ S<[ B<-C [I<number/list>] >]>
S<[ B<-S> ]>
S<[ B<-x>[I<dir>] ]>
S<[ B<-i>[I<extension>] ]>
- S<[ B<-e> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
- S<[ B<-A [I<assertions>] >]>
- S<[ B<-C [I<number/list>] >]>
+ S<[ [B<-e>|B<-E>] I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
=head1 DESCRIPTION
=item 1.
-Specified line by line via B<-e> switches on the command line.
+Specified line by line via B<-e> or B<-E> switches on the command line.
=item 2.
The sequences "-*" and "- " are specifically ignored so that you could,
if you were so inclined, say
- #!/bin/sh -- # -*- perl -*- -p
- eval 'exec perl -wS $0 ${1+"$@"}'
- if $running_under_some_shell;
+ #!/bin/sh
+ #! -*-perl-*-
+ eval 'exec perl -x -wS $0 ${1+"$@"}'
+ if 0;
to let Perl see the B<-p> switch.
C<exit(0)> is provided to indicate successful completion.
=head2 #! and quoting on non-Unix systems
+X<hashbang> X<#!>
Unix's #! technique can be simulated on other systems:
this means you can no longer tell the difference between an executable
Perl program and a Perl library file.
-=item Macintosh
-
-A Macintosh perl program will have the appropriate Creator and
-Type, so that double-clicking them will invoke the perl application.
-
=item VMS
Put
# MS-DOS, etc.
perl -e "print \"Hello world\n\""
- # Macintosh
- print "Hello world\n"
- (then Run "Myscript" or Shift-Command-R)
-
# VMS
perl -e "print ""Hello world\n"""
when nobody was looking, but just try to find documentation for its
quoting rules.
-Under the Macintosh, it depends which environment you are using. The MacPerl
-shell, or MPW, is much like Unix shells in its support for several
-quoting variants, except that it makes free use of the Macintosh's non-ASCII
-characters as control characters.
-
There is no general solution to all of this. It's just a mess.
=head2 Location of Perl
+X<perl, location of interpreter>
It may seem obvious to say, but Perl is useful only when users can
easily find it. When possible, it's good for both F</usr/bin/perl>
use 5.005_54;
=head2 Command Switches
+X<perl, command switches> X<command switches>
As with all standard commands, a single-character switch may be
clustered with the following switch, if any.
=over 5
=item B<-0>[I<octal/hexadecimal>]
+X<-0> X<$/>
specifies the input record separator (C<$/>) as an octal or
hexadecimal number. If there are no digits, the null character is the
(This means that you cannot use the C<-x> with a directory name that
consists of hexadecimal digits.)
-=item B<-A [I<assertions>]>
-
-Activates the assertions given after the switch as a comma-separated
-list of assertion names. If no assertion name is given, activates all
-assertions. See L<assertions>.
-
=item B<-a>
+X<-a> X<autosplit>
turns on autosplit mode when used with a B<-n> or B<-p>. An implicit
split command to the @F array is done as the first thing inside the
An alternate delimiter may be specified using B<-F>.
=item B<-C [I<number/list>]>
+X<-C>
-The C<-C> flag controls some Unicode of the Perl Unicode features.
+The C<-C> flag controls some of the Perl Unicode features.
As of 5.8.1, the C<-C> can be followed either by a number or a list
of option letters. The letters, their numeric values, and effects
variables (the LC_ALL, LC_TYPE, and LANG, in the order
of decreasing precedence) -- if the variables indicate
UTF-8, then the selected "IOEioA" are in effect
+ a 256 Set ${^UTF8CACHE} to -1, to run the UTF-8 caching code in
+ debugging mode.
+
+=for documenting_the_underdocumented
+perl.h gives W/128 as PERL_UNICODE_WIDESYSCALLS "/* for Sarathy */"
+
+=for todo
+perltodo mentions Unicode in %ENV and filenames. I guess that these will be
+options e and f (or F).
For example, C<-COE> and C<-C6> will both turn on UTF-8-ness on both
STDOUT and STDERR. Repeating letters is just redundant, not cumulative
streams as usual.
C<-C> on its own (not followed by any number or option list), or the
-empty string C<""> for the C<$ENV{PERL_UNICODE}, has the same effect
-as C<-CSDL>. In other words, the standard I/O handles and the default
-C<open()> layer are UTF-8-fied B<but> only if the locale environment
-variables indicate a UTF-8 locale. This behaviour follows the
-I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0.
+empty string C<""> for the C<PERL_UNICODE> environment variable, has the
+same effect as C<-CSDL>. In other words, the standard I/O handles and
+the default C<open()> layer are UTF-8-fied B<but> only if the locale
+environment variables indicate a UTF-8 locale. This behaviour follows
+the I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0.
-You can use C<-C0> (or C<"0"> for $ENV{PERL_UNICODE}) to explicitly
+You can use C<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly
disable all the above Unicode features.
The read-only magic variable C<${^UNICODE}> reflects the numeric value
-of this setting. This is variable is set during Perl startup and is
+of this setting. This variable is set during Perl startup and is
thereafter read-only. If you want runtime effects, use the three-arg
open() (see L<perlfunc/open>), the two-arg binmode() (see L<perlfunc/binmode>),
and the C<open> pragma (see L<open>).
This feature was practically unused, however, and the command line
switch was therefore "recycled".)
+B<Note:> Since perl 5.10.1, if the -C option is used on the #! line, it
+must be specified on the command line as well, since the standard streams
+are already set up at this point in the execution of the perl interpreter.
+You can also use binmode() to set the encoding of an I/O stream.
+
=item B<-c>
+X<-c>
causes Perl to check the syntax of the program and then exit without
-executing it. Actually, it I<will> execute C<BEGIN>, C<CHECK>, and
-C<use> blocks, because these are considered as occurring outside the
-execution of your program. C<INIT> and C<END> blocks, however, will
-be skipped.
+executing it. Actually, it I<will> execute C<BEGIN>, C<UNITCHECK>,
+C<CHECK>, and C<use> blocks, because these are considered as occurring
+outside the execution of your program. C<INIT> and C<END> blocks,
+however, will be skipped.
=item B<-d>
+X<-d> X<-dt>
+
+=item B<-dt>
runs the program under the Perl debugger. See L<perldebug>.
+If B<t> is specified, it indicates to the debugger that threads
+will be used in the code being debugged.
=item B<-d:>I<foo[=bar,baz]>
+X<-d> X<-dt>
+
+=item B<-dt:>I<foo[=bar,baz]>
runs the program under the control of a debugging, profiling, or
tracing module installed as Devel::foo. E.g., B<-d:DProf> executes
flag, options may be passed to the Devel::foo package where they
will be received and interpreted by the Devel::foo::import routine.
The comma-separated list of options must follow a C<=> character.
+If B<t> is specified, it indicates to the debugger that threads
+will be used in the code being debugged.
See L<perldebug>.
=item B<-D>I<letters>
+X<-D> X<DEBUGGING> X<-DDEBUGGING>
=item B<-D>I<number>
As an alternative, specify a number instead of list of letters (e.g.,
B<-D14> is equivalent to B<-Dtls>):
- 1 p Tokenizing and parsing
- 2 s Stack snapshots
- with v, displays all stacks
+ 1 p Tokenizing and parsing (with v, displays parse stack)
+ 2 s Stack snapshots (with v, displays all stacks)
4 l Context (loop) stack processing
8 t Trace execution
16 o Method and overloading resolution
32 c String/numeric conversions
- 64 P Print profiling info, preprocessor command for -P, source file input state
- 128 m Memory allocation
+ 64 P Print profiling info, source file input state
+ 128 m Memory and SV allocation
256 f Format processing
512 r Regular expression parsing and execution
1024 x Syntax tree dump
2048 u Tainting checks
- 4096 (Obsolete, previously used for LEAKTEST)
+ 4096 U Unofficial, User hacking (reserved for private, unreleased use)
8192 H Hash dump -- usurps values()
16384 X Scratchpad allocation
32768 D Cleaning up
- 65536 S Thread synchronization
131072 T Tokenising
262144 R Include reference counts of dumped variables (eg when using -Ds)
524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
1048576 v Verbose: use in conjunction with other flags
2097152 C Copy On Write
+ 4194304 A Consistency checks on internal structures
+ 8388608 q quiet - currently only suppresses the "EXECUTING" message
+ 16777216 M trace smart match resolution
+ 33554432 B dump suBroutine definitions, including special Blocks like BEGIN
All these flags require B<-DDEBUGGING> when you compile the Perl
executable (but see L<Devel::Peek>, L<re> which may change this).
you can't use Perl's B<-D> switch. Instead do this
# If you have "env" utility
- env=PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
+ env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
# Bourne shell syntax
$ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program
See L<perldebug> for details and variations.
=item B<-e> I<commandline>
+X<-e>
may be used to enter one line of program. If B<-e> is given, Perl
will not look for a filename in the argument list. Multiple B<-e>
commands may be given to build up a multi-line script. Make sure
to use semicolons where you would in a normal program.
+=item B<-E> I<commandline>
+X<-E>
+
+behaves just like B<-e>, except that it implicitly enables all
+optional features (in the main compilation unit). See L<feature>.
+
+=item B<-f>
+X<-f> X<sitecustomize> X<sitecustomize.pl>
+
+Disable executing F<$Config{sitelib}/sitecustomize.pl> at startup.
+
+Perl can be built so that it by default will try to execute
+F<$Config{sitelib}/sitecustomize.pl> at startup (in a BEGIN block).
+This is a hook that allows the sysadmin to customize how perl behaves.
+It can for instance be used to add entries to the @INC array to make perl
+find modules in non-standard locations.
+
+Perl actually inserts the following code:
+
+ BEGIN {
+ do { local $!; -f "$Config{sitelib}/sitecustomize.pl"; }
+ && do "$Config{sitelib}/sitecustomize.pl";
+ }
+
+Since it is an actual C<do> (not a C<require>), F<sitecustomize.pl>
+doesn't need to return a true value. The code is run in package C<main>,
+in its own lexical scope. However, if the script dies, C<$@> will not
+be set.
+
+The value of C<$Config{sitelib}> is also determined in C code and not
+read from C<Config.pm>, which is not loaded.
+
+The code is executed B<very> early. For example, any changes made to
+C<@INC> will show up in the output of `perl -V`. Of course, C<END>
+blocks will be likewise executed very late.
+
+To determine at runtime if this capability has been compiled in your
+perl, you can check the value of C<$Config{usesitecustomize}>.
+
=item B<-F>I<pattern>
+X<-F>
specifies the pattern to split on if B<-a> is also in effect. The
pattern may be surrounded by C<//>, C<"">, or C<''>, otherwise it will be
-put in single quotes.
+put in single quotes. You can't use literal whitespace in the pattern.
=item B<-h>
+X<-h>
prints a summary of the options.
=item B<-i>[I<extension>]
+X<-i> X<in-place>
specifies that files processed by the C<E<lt>E<gt>> construct are to be
edited in-place. It does this by renaming the input file, opening the
$ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
+Note that because B<-i> renames or deletes the original file before
+creating a new file of the same name, Unix-style soft and hard links will
+not be preserved.
+
Finally, the B<-i> switch does not impede execution when no
files are given on the command line. In this case, no backup is made
(the original file cannot, of course, be determined) and processing
proceeds from STDIN to STDOUT as might be expected.
=item B<-I>I<directory>
+X<-I> X<@INC>
Directories specified by B<-I> are prepended to the search path for
-modules (C<@INC>), and also tells the C preprocessor where to search for
-include files. The C preprocessor is invoked with B<-P>; by default it
-searches /usr/include and /usr/lib/perl.
+modules (C<@INC>).
=item B<-l>[I<octnum>]
+X<-l> X<$/> X<$\>
enables automatic line-ending processing. It has two separate
effects. First, it automatically chomps C<$/> (the input record
This sets C<$\> to newline and then sets C<$/> to the null character.
=item B<-m>[B<->]I<module>
+X<-m> X<-M>
=item B<-M>[B<->]I<module>
C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
removes the distinction between B<-m> and B<-M>.
+A consequence of this is that B<-MFoo=number> never does a version check
+(unless C<Foo::import()> itself is set up to do a version check, which
+could happen for example if Foo inherits from Exporter.)
+
=item B<-n>
+X<-n>
causes Perl to assume the following loop around your program, which
makes it iterate over filename arguments somewhat like B<sed -n> or
lines printed. If a file named by an argument cannot be opened for
some reason, Perl warns you about it and moves on to the next file.
-Here is an efficient way to delete all files older than a week:
+Also note that C<< <> >> passes command line arguments to
+L<perlfunc/open>, which doesn't necessarily interpret them as file names.
+See L<perlop> for possible security implications.
+
+Here is an efficient way to delete all files that haven't been modified for
+at least a week:
find . -mtime +7 -print | perl -nle unlink
the implicit program loop, just as in B<awk>.
=item B<-p>
+X<-p>
causes Perl to assume the following loop around your program, which
makes it iterate over filename arguments somewhat like B<sed>:
C<BEGIN> and C<END> blocks may be used to capture control before or after
the implicit loop, just as in B<awk>.
-=item B<-P>
-
-B<NOTE: Use of -P is strongly discouraged because of its inherent
-problems, including poor portability.>
-
-This option causes your program to be run through the C preprocessor before
-compilation by Perl. Because both comments and B<cpp> directives begin
-with the # character, you should avoid starting comments with any words
-recognized by the C preprocessor such as C<"if">, C<"else">, or C<"define">.
-
-If you're considering using C<-P>, you might also want to look at the
-Filter::cpp module from CPAN.
-
-The problems of -P include, but are not limited to:
-
-=over 10
-
-=item *
-
-The C<#!> line is stripped, so any switches there don't apply.
-
-=item *
-
-A C<-P> on a C<#!> line doesn't work.
-
-=item *
-
-B<All> lines that begin with (whitespace and) a C<#> but
-do not look like cpp commands, are stripped, including anything
-inside Perl strings, regular expressions, and here-docs .
-
-=item *
-
-In some platforms the C preprocessor knows too much: it knows about
-the C++ -style until-end-of-line comments starting with C<"//">.
-This will cause problems with common Perl constructs like
-
- s/foo//;
-
-because after -P this will became illegal code
-
- s/foo
-
-The workaround is to use some other quoting separator than C<"/">,
-like for example C<"!">:
-
- s!foo!!;
-
-
-
-=item *
-
-It requires not only a working C preprocessor but also a working
-F<sed>. If not on UNIX, you are probably out of luck on this.
-
-=item *
-
-Script line numbers are not preserved.
-
-=item *
-
-The C<-x> does not work with C<-P>.
-
-=back
-
=item B<-s>
+X<-s>
enables rudimentary switch parsing for switches on the command
line after the program name but before any filename arguments (or before
-an argument of B<-->). This means you can have switches with two leading
-dashes (B<--help>). Any switch found there is removed from @ARGV and sets the
+an argument of B<-->). Any switch found there is removed from @ARGV and sets the
corresponding variable in the Perl program. The following program
prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
if it is invoked with B<-xyz=abc>.
#!/usr/bin/perl -s
if ($xyz) { print "$xyz\n" }
-Do note that B<--help> creates the variable ${-help}, which is not compliant
-with C<strict refs>.
+Do note that a switch like B<--help> creates the variable ${-help}, which is not compliant
+with C<strict refs>. Also, when using this option on a script with
+warnings enabled you may get a lot of spurious "used only once" warnings.
=item B<-S>
+X<-S>
makes Perl use the PATH environment variable to search for the
program (unless the name of the program contains directory separators).
of those suffixes. If your Perl was compiled with DEBUGGING turned
on, using the -Dp switch to Perl shows how the search progresses.
-Typically this is used to emulate #! startup on platforms that
-don't support #!. This example works on many platforms that
-have a shell compatible with Bourne shell:
+Typically this is used to emulate #! startup on platforms that don't
+support #!. Its also convenient when debugging a script that uses #!,
+and is thus normally found by the shell's $PATH search mechanism.
+
+This example works on many platforms that have a shell compatible with
+Bourne shell:
#!/usr/bin/perl
eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
program will be searched for strictly on the PATH.
=item B<-t>
+X<-t>
Like B<-T>, but taint checks will issue warnings rather than fatal
errors. These warnings can be controlled normally with C<no warnings
always use the real B<-T>.
=item B<-T>
+X<-T>
forces "taint" checks to be turned on so you can test them. Ordinarily
these checks are done only when running setuid or setgid. It's a
that construct.
=item B<-u>
+X<-u>
This obsolete switch causes Perl to dump core after compiling your
program. You can then in theory take this core dump and turn it
operator instead. Note: availability of B<undump> is platform
specific and may not be available for a specific port of Perl.
-This switch has been superseded in favor of the new Perl code
-generator backends to the compiler. See L<B> and L<B::Bytecode>
-for details.
-
=item B<-U>
+X<-U>
allows Perl to do unsafe operations. Currently the only "unsafe"
-operations are the unlinking of directories while running as superuser,
-and running setuid programs with fatal taint checks turned into
-warnings. Note that the B<-w> switch (or the C<$^W> variable) must
-be used along with this option to actually I<generate> the
-taint-check warnings.
+operations are attempting to unlink directories while running as
+superuser, and running setuid programs with fatal taint checks turned
+into warnings. Note that the B<-w> switch (or the C<$^W> variable)
+must be used along with this option to actually I<generate> the
+taint-check warnings.
=item B<-v>
+X<-v>
prints the version and patchlevel of your perl executable.
=item B<-V>
+X<-V>
prints summary of the major perl configuration values and the current
values of @INC.
-=item B<-V:>I<name>
+=item B<-V:>I<configvar>
+
+Prints to STDOUT the value of the named configuration variable(s),
+with multiples when your configvar argument looks like a regex (has
+non-letters). For example:
+
+ $ perl -V:libc
+ libc='/lib/libc-2.2.4.so';
+ $ perl -V:lib.
+ libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
+ libc='/lib/libc-2.2.4.so';
+ $ perl -V:lib.*
+ libpth='/usr/local/lib /lib /usr/lib';
+ libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
+ lib_ext='.a';
+ libc='/lib/libc-2.2.4.so';
+ libperl='libperl.a';
+ ....
-Prints to STDOUT the value of the named configuration variable.
-For example,
+Additionally, extra colons can be used to control formatting. A
+trailing colon suppresses the linefeed and terminator ';', allowing
+you to embed queries into shell commands. (mnemonic: PATH separator
+':'.)
- $ perl -V:man.dir
+ $ echo "compression-vars: " `perl -V:z.*: ` " are here !"
+ compression-vars: zcat='' zip='zip' are here !
-will provide strong clues about what your MANPATH variable should
-be set to in order to access the Perl documentation.
+A leading colon removes the 'name=' part of the response, this allows
+you to map to the name you need. (mnemonic: empty label)
+
+ $ echo "goodvfork="`./perl -Ilib -V::usevfork`
+ goodvfork=false;
+
+Leading and trailing colons can be used together if you need
+positional parameter values without the names. Note that in the case
+below, the PERL_API params are returned in alphabetical order.
+
+ $ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
+ building_on 'linux' '5' '1' '9' now
=item B<-w>
+X<-w>
prints warnings about dubious constructs, such as variable names
that are mentioned only once and scalar variables that are used
before being set, redefined subroutines, references to undefined
filehandles or filehandles opened read-only that you are attempting
-to write on, values used as a number that doesn't look like numbers,
+to write on, values used as a number that don't look like numbers,
using an array as though it were a scalar, if your subroutines
recurse more than 100 deep, and innumerable other things.
of warnings; see L<warnings> or L<perllexwarn>.
=item B<-W>
+X<-W>
Enables all warnings regardless of C<no warnings> or C<$^W>.
See L<perllexwarn>.
=item B<-X>
+X<-X>
Disables all warnings regardless of C<use warnings> or C<$^W>.
See L<perllexwarn>.
-=item B<-x> I<directory>
+=item B<-x>
+X<-x>
+
+=item B<-x>I<directory>
tells Perl that the program is embedded in a larger chunk of unrelated
ASCII text, such as in a mail message. Leading garbage will be
discarded until the first line that starts with #! and contains the
string "perl". Any meaningful switches on that line will be applied.
+
+All references to line numbers by the program (warnings, errors, ...)
+will treat the #! line as the first line.
+Thus a warning on the 2nd line of the program (which is on the 100th
+line in the file) will be reported as line 2, and not as line 100.
+This can be overridden by using the #line directive.
+(See L<perlsyn/"Plain-Old-Comments-(Not!)">)
+
If a directory name is specified, Perl will switch to that directory
before running the program. The B<-x> switch controls only the
disposal of leading garbage. The program must be terminated with
can process any or all of the trailing garbage via the DATA filehandle
if desired).
+The directory, if specified, must appear immediately following the B<-x>
+with no intervening whitespace.
+
=back
=head1 ENVIRONMENT
+X<perl, environment variables>
=over 12
=item HOME
+X<HOME>
Used if chdir has no argument.
=item LOGDIR
+X<LOGDIR>
Used if chdir has no argument and HOME is not set.
=item PATH
+X<PATH>
Used in executing subprocesses, and in finding the program if B<-S> is
used.
=item PERL5LIB
+X<PERL5LIB>
A list of directories in which to look for Perl library
files before looking in the standard library and the current
directory. Any architecture-specific directories under the specified
-locations are automatically included if they exist. If PERL5LIB is not
-defined, PERLLIB is used. Directories are separated (like in PATH) by
-a colon on unixish platforms and by a semicolon on Windows (the proper
-path separator being given by the command C<perl -V:path_sep>).
+locations are automatically included if they exist (this lookup
+being done at interpreter startup time.)
+
+If PERL5LIB is not defined, PERLLIB is used. Directories are separated
+(like in PATH) by a colon on Unixish platforms and by a semicolon on
+Windows (the proper path separator being given by the command C<perl
+-V:path_sep>).
When running taint checks (either because the program was running setuid
-or setgid, or the B<-T> switch was used), neither variable is used.
-The program should instead say:
+or setgid, or the B<-T> or B<-t> switch was specified), neither variable
+is used. The program should instead say:
use lib "/my/directory";
=item PERL5OPT
+X<PERL5OPT>
Command-line options (switches). Switches in this variable are taken
-as if they were on every Perl command line. Only the B<-[DIMUdmtw]>
+as if they were on every Perl command line. Only the B<-[CDIMUdmtwW]>
switches are allowed. When running taint checks (because the program
was running setuid or setgid, or the B<-T> switch was used), this
variable is ignored. If PERL5OPT begins with B<-T>, tainting will be
enabled, and any subsequent options ignored.
=item PERLIO
+X<PERLIO>
A space (or colon) separated list of PerlIO layers. If perl is built
to use PerlIO system for IO (the default) these layers effect perl's IO.
layer specification strings (which is also used to decode the PERLIO
environment variable) treats the colon as a separator.
-An unset or empty PERLIO is equivalent to C<:stdio>.
+An unset or empty PERLIO is equivalent to the default set of layers for
+your platform, for example C<:unix:perlio> on Unix-like systems
+and C<:unix:crlf> on Windows and other DOS-like systems.
The list becomes the default for I<all> perl's IO. Consequently only built-in
layers can appear in this list, as external layers (such as :encoding()) need
encodings as defaults.
The layers that it makes sense to include in the PERLIO environment
-variable are summarised below. For more details see L<PerlIO>.
+variable are
briefly summarised below. For more details see L<PerlIO>.
=over 8
=item :bytes
+X<:bytes>
A pseudolayer that turns I<off> the C<:utf8> flag for the layer below.
Unlikely to be useful on its own in the global PERLIO environment variable.
You perhaps were thinking of C<:crlf:bytes> or C<:perlio:bytes>.
=item :crlf
+X<:crlf>
-A layer that implements DOS/Windows like CRLF line endings. On read
-converts pairs of CR,LF to a single "\n" newline character. On write
-converts each "\n" to a CR,LF pair. Note that this layer likes to be
-one of its kind: it silently ignores attempts to be pushed into the
-layer stack more than once.
-
-(Gory details follow) To be more exact what happens is this: after
-pushing itself to the stack, the C<:crlf> layer checks all the layers
-below itself to find the first layer that is capable of being a CRLF
-layer but is not yet enabled to be a CRLF layer. If it finds such a
-layer, it enables the CRLFness of that other deeper layer, and then
-pops itself off the stack. If not, fine, use the one we just pushed.
-
-The end result is that a C<:crlf> means "please enable the first CRLF
-layer you can find, and if you can't find one, here would be a good
-spot to place a new one."
-
-Based on the C<:perlio> layer.
+A layer which does CRLF to "\n" translation distinguishing "text" and
+"binary" files in the manner of MS-DOS and similar operating systems.
+(It currently does I<not> mimic MS-DOS as far as treating of Control-Z
+as being an end-of-file marker.)
=item :mmap
+X<:mmap>
A layer which implements "reading" of files by using C<mmap()> to
make (whole) file appear in the process's address space, and then
-using that as PerlIO's "buffer". This I<may> be faster in certain
-circumstances for large files, and may result in less physical memory
-use when multiple processes are reading the same file.
-
-Files which are not C<mmap()>-able revert to behaving like the C<:perlio>
-layer. Writes also behave like C<:perlio> layer as C<mmap()> for write
-needs extra house-keeping (to extend the file) which negates any advantage.
-
-The C<:mmap> layer will not exist if platform does not support C<mmap()>.
+using that as PerlIO's "buffer".
=item :perlio
+X<:perlio>
-A from scratch implementation of buffering for PerlIO. Provides fast
-access to the buffer for C<sv_gets> which implements perl's readline/E<lt>E<gt>
-and in general attempts to minimize data copying.
-
-C<:perlio> will insert a C<:unix> layer below itself to do low level IO.
+This is a re-implementation of "stdio-like" buffering written as a
+PerlIO "layer". As such it will call whatever layer is below it for
+its operations (typically C<:unix>).
=item :pop
+X<:pop>
An experimental pseudolayer that removes the topmost layer.
-Use with the same care as is reserved for nitroglyserin.
+Use with the same care as is reserved for nitroglycerin.
=item :raw
+X<:raw>
-A pseudolayer that manipulates other layers. Applying the <:raw>
+A pseudolayer that manipulates other layers. Applying the C<:raw>
layer is equivalent to calling C<binmode($fh)>. It makes the stream
pass each byte as-is without any translation. In particular CRLF
translation, and/or :utf8 intuited from locale are disabled.
-Arranges for all accesses go straight to the lowest buffered layer provided
-by the configration. That is it strips off any layers above that layer.
-
-In Perl 5.6 and some books the C<:raw> layer (previously sometimes also
-referred to as a "discipline") is documented as the inverse of the
-C<:crlf> layer. That is no longer the case - other layers which would
-alter binary nature of the stream are also disabled. If you want UNIX
-line endings on a platform that normally does CRLF translation, but still
-want UTF-8 or encoding defaults the appropriate thing to do is to add
-C<:perlio> to PERLIO environment variable.
+Unlike in the earlier versions of Perl C<:raw> is I<not>
+just the inverse of C<:crlf> - other layers which would affect the
+binary nature of the stream are also removed or disabled.
=item :stdio
+X<:stdio>
This layer provides PerlIO interface by wrapping system's ANSI C "stdio"
library calls. The layer provides both buffering and IO.
to do that.
=item :unix
+X<:unix>
-Lowest level layer which provides basic PerlIO operations in terms of
-UNIX/POSIX numeric file descriptor calls
-C<open(), read(), write(), lseek(), close()>
+Low level layer which calls C<read>, C<write> and C<lseek> etc.
=item :utf8
+X<:utf8>
A pseudolayer that turns on a flag on the layer below to tell perl
-that data sent to the stream should be converted to perl internal
-"utf8" form and that data from the stream should be considered as so
-encoded. On ASCII based platforms the encoding is UTF-8 and on EBCDIC
-platforms UTF-EBCDIC. May be useful in PERLIO environment variable to
-make UTF-8 the default. (To turn off that behaviour use C<:bytes>
-layer.)
+that output should be in utf8 and that input should be regarded as
+already in valid utf8 form. It does not check for validity and as such
+should be handled with caution for input. Generally C<:encoding(utf8)> is
+the best option when reading UTF-8 encoded data.
=item :win32
+X<:win32>
On Win32 platforms this I<experimental> layer uses native "handle" IO
rather than unix-like numeric file descriptor layer. Known to be
On all platforms the default set of layers should give acceptable results.
-For UNIX platforms that will equivalent of "unix perlio" or "stdio".
+For Unix platforms that will equivalent of "unix perlio" or "stdio".
Configure is setup to prefer "stdio" implementation if system's library
provides for fast access to the buffer, otherwise it uses the "unix perlio"
implementation.
This release uses C<unix> as the bottom layer on Win32 and so still uses C
compiler's numeric file descriptor routines. There is an experimental native
-C<win32> layer which is expected to be enhanced and should eventually replace
-the C<unix> layer.
+C<win32> layer which is expected to be enhanced and should eventually be
+the default under Win32.
+
+The PERLIO environment variable is completely ignored when perl
+is run in taint mode.
=item PERLIO_DEBUG
+X<PERLIO_DEBUG>
If set to the name of a file or device then certain operations of PerlIO
sub-system will be logged to that file (opened as append). Typical uses
-are UNIX:
+are Unix:
PERLIO_DEBUG=/dev/tty perl script ...
set PERLIO_DEBUG=CON
perl script ...
+This functionality is disabled for setuid scripts and for scripts run
+with B<-T>.
=item PERLLIB
+X<PERLLIB>
A list of directories in which to look for Perl library
files before looking in the standard library and the current directory.
If PERL5LIB is defined, PERLLIB is not used.
+The PERLLIB environment variable is completely ignored when perl
+is run in taint mode.
+
=item PERL5DB
+X<PERL5DB>
The command used to load the debugger code. The default is:
BEGIN { require 'perl5db.pl' }
+The PERL5DB environment variable only used when perl is started with
+a bare B<-d> switch.
+
+=item PERL5DB_THREADED
+X<PERL5DB_THREADED>
+
+If set to a true value, indicates to the debugger that the code being
+debugged uses threads.
+
=item PERL5SHELL (specific to the Win32 port)
+X<PERL5SHELL>
May be set to an alternative shell that perl must use internally for
executing "backtick" commands or system(). Default is C<cmd.exe /x/d/c>
interfere with the proper functioning of other programs (which usually
look in COMSPEC to find a shell fit for interactive use).
+Before Perl 5.10.0 and 5.8.8, PERL5SHELL was not taint checked
+when running external commands. It is recommended that
+you explicitly set (or delete) C<$ENV{PERL5SHELL}> when running
+in taint mode under Windows.
+
+=item PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
+X<PERL_ALLOW_NON_IFS_LSP>
+
+Set to 1 to allow the use of non-IFS compatible LSP's.
+Perl normally searches for an IFS-compatible LSP because this is required
+for its emulation of Windows sockets as real filehandles. However, this may
+cause problems if you have a firewall such as McAfee Guardian which requires
+all applications to use its LSP which is not IFS-compatible, because clearly
+Perl will normally avoid using such an LSP.
+Setting this environment variable to 1 means that Perl will simply use the
+first suitable LSP enumerated in the catalog, which keeps McAfee Guardian
+happy (and in that particular case Perl still works too because McAfee
+Guardian's LSP actually plays some other games which allow applications
+requiring IFS compatibility to work).
+
=item PERL_DEBUG_MSTATS
+X<PERL_DEBUG_MSTATS>
Relevant only if perl is compiled with the malloc included with the perl
distribution (that is, if C<perl -V:d_mymalloc> is 'define').
after compilation.
=item PERL_DESTRUCT_LEVEL
+X<PERL_DESTRUCT_LEVEL>
Relevant only if your perl executable was built with B<-DDEBUGGING>,
this controls the behavior of global destruction of objects and other
references. See L<perlhack/PERL_DESTRUCT_LEVEL> for more information.
+=item PERL_DL_NONLAZY
+X<PERL_DL_NONLAZY>
+
+Set to one to have perl resolve B<all> undefined symbols when it loads
+a dynamic library. The default behaviour is to resolve symbols when
+they are used. Setting this variable is useful during testing of
+extensions as it ensures that you get an error on misspelled function
+names even if the test suite doesn't call it.
+
=item PERL_ENCODING
+X<PERL_ENCODING>
If using the C<encoding> pragma without an explicit encoding name, the
PERL_ENCODING environment variable is consulted for an encoding name.
=item PERL_HASH_SEED
+X<PERL_HASH_SEED>
-(Since Perl 5.8.1.) Used to randomise Perl's internal hash function.
+(Since Perl 5.8.1.) Used to randomise perl's internal hash function.
To emulate the pre-5.8.1 behaviour, set to an integer (zero means
exactly the same order as 5.8.0). "Pre-5.8.1" means, among other
-things, that hash keys will be ordered the same between different runs
-of Perl.
+things, that hash keys will always have the same ordering between
+different runs of perl.
+
+Most hashes return elements in the same order as Perl 5.8.0 by default.
+On a hash by hash basis, if pathological data is detected during a hash
+key insertion, then that hash will switch to an alternative random hash
+seed.
The default behaviour is to randomise unless the PERL_HASH_SEED is set.
-If Perl has been compiled with C<-DUSE_HASH_SEED_EXPLICIT>, the default
+If perl has been compiled with C<-DUSE_HASH_SEED_EXPLICIT>, the default
behaviour is B<not> to randomise unless the PERL_HASH_SEED is set.
-If PERL_HASH_SEED is unset or set to a non-numeric string, Perl uses
+If PERL_HASH_SEED is unset or set to a non-numeric string, perl uses
the pseudorandom seed supplied by the operating system and libraries.
-This means that each different run of Perl will have a different
-ordering of the results of keys(), values(), and each().
B<Please note that the hash seed is sensitive information>. Hashes are
randomized to protect against local and remote attacks against Perl
L</PERL_HASH_SEED_DEBUG> for more information.
=item PERL_HASH_SEED_DEBUG
+X<PERL_HASH_SEED_DEBUG>
(Since Perl 5.8.1.) Set to one to display (to STDERR) the value of
the hash seed at the beginning of execution. This, combined with
B<Do not disclose the hash seed> to people who don't need to know it.
See also hash_seed() of L<Hash::Util>.
+=item PERL_MEM_LOG
+X<PERL_MEM_LOG>
+
+If your perl was configured with C<-Accflags=-DPERL_MEM_LOG>, setting the
+environment variable C<PERL_MEMLOG> enables logging debug messages. The
+value has the form C<< <number>[m][s][t] >>, where C<number> is the
+filedescriptor number you want to write to, and the combination of letters
+specifies that you want information about (m)emory and/or (s)v, optionally
+with (t)imestamps. For example C<PERL_MEMLOG=1mst> will log all
+information to stdout. You can write to other opened filedescriptors too,
+in a variety of ways;
+
+ bash$ 3>foo3 PERL_MEM_LOG=3m perl ...
+
=item PERL_ROOT (specific to the VMS port)
+X<PERL_ROOT>
A translation concealed rooted logical name that contains perl and the
logical device for the @INC path on VMS only. Other logical names that
L<perlvms> and in F<README.vms> in the Perl source distribution.
=item PERL_SIGNALS
+X<PERL_SIGNALS>
In Perls 5.8.1 and later. If set to C<unsafe> the pre-Perl-5.8.0
signals behaviour (immediate but unsafe) is restored. If set to
C<safe> the safe (or deferred) signals are used.
-See L<perlipc/"Deferred Signals (Safe signals)">.
+See L<perlipc/"Deferred Signals (Safe Signals)">.
=item PERL_UNICODE
+X<PERL_UNICODE>
Equivalent to the B<-C> command-line switch. Note that this is not
-a boolean variable-- setting this to C<"1"> is not the right way to
+a boolean variable. Setting this to C<"1"> is not the right way to
"enable Unicode" (whatever that would mean). You can use C<"0"> to
"disable Unicode", though (or alternatively unset PERL_UNICODE in
your shell before starting Perl). See the description of the C<-C>
switch for more information.
=item SYS$LOGIN (specific to the VMS port)
+X<SYS$LOGIN>
Used if chdir has no argument and HOME and LOGDIR are not set.
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