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<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ] [ B<-f> ]>
+ S<[ B<-A>[I<module>][=I<assertions>] ]>
+ S<[ B<-C [I<number/list>] >]>
S<[ B<-P> ]>
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<-eE> 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.
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:
=item Macintosh
-A Macintosh perl program will have the appropriate Creator and
-Type, so that double-clicking them will invoke the perl application.
+Under "Classic" MacOS, a perl program will have the appropriate Creator and
+Type, so that double-clicking them will invoke the MacPerl application.
+Under Mac OS X, clickable apps can be made from any C<#!> script using Wil
+Sanchez' DropScript utility: http://www.wsanchez.net/software/ .
=item VMS
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>]>
+=item B<-A[I<module>][=I<assertions>]>
+X<-A>
+
+Activates the assertions given after the equal sign as a comma-separated
+list of assertion names or regular expressions. If no assertion name
+is given, activates all assertions.
+
+The module L<assertions::activate> is used by default to activate the
+selected assertions. An alternate module may be specified including
+its name between the switch and the equal sign.
-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>.
+See L<assertions> and L<assertions::activate>.
=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.
of option letters. The letters, their numeric values, and effects
are as follows; listing the letters is equal to summing the numbers.
- I 1 STDIN is assumed to be in UTF-8
- O 2 STDOUT will be in UTF-8
- E 4 STDERR will be in UTF-8
- S 7 I + O + E
- i 8 UTF-8 is the default PerlIO layer for input streams
- o 16 UTF-8 is the default PerlIO layer for output streams
- D 24 i + o
- A 32 the @ARGV elements are expected to be strings encoded in UTF-8
- L 64 normally the "IOEioA" are unconditional,
- the L makes them conditional on the locale environment
- 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
+ I 1 STDIN is assumed to be in UTF-8
+ O 2 STDOUT will be in UTF-8
+ E 4 STDERR will be in UTF-8
+ S 7 I + O + E
+ i 8 UTF-8 is the default PerlIO layer for input streams
+ o 16 UTF-8 is the default PerlIO layer for output streams
+ D 24 i + o
+ A 32 the @ARGV elements are expected to be strings encoded
+ in UTF-8
+ L 64 normally the "IOEioA" are unconditional,
+ the L makes them conditional on the locale environment
+ 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 <-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
switch was therefore "recycled".)
=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
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
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
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>
+
+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. 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.
+
=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
This allows you to add a prefix to the backup file, instead of (or in
addition to) a suffix:
- $ perl -pi 'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
+ $ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to 'orig_fileA'
Or even to place backup copies of the original files into another
directory (provided the directory already exists):
- $ perl -pi 'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
+ $ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'
These sets of one-liners are equivalent:
$ perl -pi -e 's/bar/baz/' fileA # overwrite current file
- $ perl -pi '*' -e 's/bar/baz/' fileA # overwrite current file
+ $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file
- $ perl -pi '.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
- $ perl -pi '*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
+ $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
+ $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
From the shell, saying
$ 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
searches /usr/include and /usr/lib/perl.
=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<$/> to the null character.
=item B<-m>[B<->]I<module>
+X<-m> X<-M>
=item B<-M>[B<->]I<module>
C<use module split(/,/,q{foo,bar})>. Note that the C<=> form
removes the distinction between B<-m> and B<-M>.
+A consequence of this is that B<-MFoo=number> never does a version check
+(unless C<Foo::import()> itself is set up to do a version check, which
+could happen for example if Foo inherits from Exporter.)
+
=item B<-n>
+X<-n>
causes Perl to assume the following loop around your program, which
makes it iterate over filename arguments somewhat like B<sed -n> or
lines printed. If a file named by an argument cannot be opened for
some reason, Perl warns you about it and moves on to the next file.
-Here is an efficient way to delete all files older than a week:
+Here is an efficient way to delete all files that haven't been modified for
+at least a week:
find . -mtime +7 -print | perl -nle unlink
the implicit program loop, just as in B<awk>.
=item B<-p>
+X<-p>
causes Perl to assume the following loop around your program, which
makes it iterate over filename arguments somewhat like B<sed>:
the implicit loop, just as in B<awk>.
=item B<-P>
+X<-P>
B<NOTE: Use of -P is strongly discouraged because of its inherent
problems, including poor portability.>
=back
=item B<-s>
+X<-s>
enables rudimentary switch parsing for switches on the command
line after the program name but before any filename arguments (or before
-an argument of B<-->). This means you can have switches with two leading
-dashes (B<--help>). Any switch found there is removed from @ARGV and sets the
+an argument of B<-->). Any switch found there is removed from @ARGV and sets the
corresponding variable in the Perl program. The following program
prints "1" if the program is invoked with a B<-xyz> switch, and "abc"
if it is invoked with B<-xyz=abc>.
#!/usr/bin/perl -s
if ($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
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>
+X<-x>
+
=item B<-x> I<directory>
tells Perl that the program is embedded in a larger chunk of unrelated
=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
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<-[CDIMUdmtwA]>
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.
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.
-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 utf8 form. May be useful in PERLIO environment
+variable to make UTF-8 the default. (To turn off that behaviour
+use C<:bytes> layer.)
=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
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.
=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
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.
=item PERL5DB
+X<PERL5DB>
The command used to load the debugger code. The default is:
BEGIN { require 'perl5db.pl' }
+=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).
+=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.
To emulate the pre-5.8.1 behaviour, set to an integer (zero means
This means that each different run of Perl will have a different
ordering of the results of keys(), values(), and each().
-See L<perlsec/"Algorithmic Complexity Attacks"> for more information.
+B<Please note that the hash seed is sensitive information>. Hashes are
+randomized to protect against local and remote attacks against Perl
+code. By manually setting a seed this protection may be partially or
+completely lost.
+
+See L<perlsec/"Algorithmic Complexity Attacks"> and
+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
+L</PERL_HASH_SEED> is intended to aid in debugging nondeterministic
+behavior caused by hash randomization.
-(Since Perl 5.8.1.) Set to "1" to display (to STDERR) the value of
-the hash seed at the beginning of execution.
+B<Note that the hash seed is sensitive information>: by knowing it one
+can craft a denial-of-service attack against Perl code, even remotely,
+see L<perlsec/"Algorithmic Complexity Attacks"> for more information.
+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_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
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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