S<[ B<-S> ]>
S<[ B<-x>[I<dir>] ]>
S<[ B<-i>[I<extension>] ]>
- S<[
B<-eE> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
+ S<[
[B<-e>|B<-E>] I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
=head1 DESCRIPTION
=item 2.
Contained in the file specified by the first filename on the command line.
-(Note that systems supporting the #! notation invoke interpreters this
+(Note that systems supporting the C<#!> notation invoke interpreters this
way. See L<Location of Perl>.)
=item 3.
With methods 2 and 3, Perl starts parsing the input file from the
beginning, unless you've specified a B<-x> switch, in which case it
-scans for the first line starting with #! and containing the word
+scans for the first line starting with C<#!> and containing the word
"perl", and starts there instead. This is useful for running a program
embedded in a larger message. (In this case you would indicate the end
of the program using the C<__END__> token.)
-The #! line is always examined for switches as the line is being
+The C<#!> line is always examined for switches as the line is being
parsed. Thus, if you're on a machine that allows only one argument
-with the #! line, or worse, doesn't even recognize the #! line, you
-still can get consistent switch behavior regardless of how Perl was
+with the C<#!> line, or worse, doesn't even recognize the C<#!> line, you
+still can get consistent switch behaviour regardless of how Perl was
invoked, even if B<-x> was used to find the beginning of the program.
Because historically some operating systems silently chopped off
-kernel interpretation of the #! line after 32 characters, some
+kernel interpretation of the C<#!> line after 32 characters, some
switches may be passed in on the command line, and some may not;
you could even get a "-" without its letter, if you're not careful.
You probably want to make sure that all your switches fall either
the 32-character boundary (if applicable), or replace the use of
B<-0>I<digits> by C<BEGIN{ $/ = "\0digits"; }>.
-Parsing of the #! switches starts wherever "perl" is mentioned in the line.
+Parsing of the C<#!> switches starts wherever "perl" is mentioned in the line.
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.
-A similar trick involves the B<env> program, if you have it.
+A similar trick involves the I<env> program, if you have it.
#!/usr/bin/env perl
The examples above use a relative path to the perl interpreter,
getting whatever version is first in the user's path. If you want
-a specific version of Perl, say, perl5.005_57, you should place
-that directly in the #! line's path.
+a specific version of Perl, say, perl5.14.1, you should place
+that directly in the C<#!> line's path.
-If the #! line does not contain the word "perl", the program named after
-the #! is executed instead of the Perl interpreter. This is slightly
-bizarre, but it helps people on machines that don't do #!, because they
-can tell a program that their SHELL is F</usr/bin/perl>, and Perl will then
-dispatch the program to the correct interpreter for them.
+If the C<#!> line does not contain the word "perl" nor the word "indir"
+the program named after the C<#!> is executed instead of the Perl
+interpreter. This is slightly bizarre, but it helps people on machines
+that don't do C<#!>, because they can tell a program that their SHELL is
+F</usr/bin/perl>, and Perl will then dispatch the program to the correct
+interpreter for them.
After locating your program, Perl compiles the entire program to an
internal form. If there are any compilation errors, execution of the
=head2 #! and quoting on non-Unix systems
X<hashbang> X<#!>
-Unix's #! technique can be simulated on other systems:
+Unix's C<#!> technique can be simulated on other systems:
=over 4
this means you can no longer tell the difference between an executable
Perl program and a Perl library file.
-=item Macintosh
-
-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
Put
- $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
- $ exit++ + ++$status != 0 and $exit = $status = undef;
+ $ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
+ $ exit++ + ++$status != 0 and $exit = $status = undef;
at the top of your program, where B<-mysw> are any command line switches you
want to pass to Perl. You can now invoke the program directly, by saying
on quoting than Unix shells. You'll need to learn the special
characters in your command-interpreter (C<*>, C<\> and C<"> are
common) and how to protect whitespace and these characters to run
-one-liners (see B<-e> below).
+one-liners (see L<-e|/-e commandline> below).
On some systems, you may have to change single-quotes to double ones,
which you must I<not> do on Unix or Plan 9 systems. You might also
# MS-DOS, etc.
perl -e "print \"Hello world\n\""
- # Macintosh
- print "Hello world\n"
- (then Run "Myscript" or Shift-Command-R)
-
# VMS
perl -e "print ""Hello world\n"""
The problem is that none of this is reliable: it depends on the
-command and it is entirely possible neither works. If B<4DOS> were
+command and it is entirely possible neither works. If I<4DOS> were
the command shell, this would probably work better:
perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
when nobody was looking, but just try to find documentation for its
quoting rules.
-Under the Macintosh, it depends which environment you are using. The MacPerl
-shell, or MPW, is much like Unix shells in its support for several
-quoting variants, except that it makes free use of the Macintosh's non-ASCII
-characters as control characters.
-
There is no general solution to all of this. It's just a mess.
=head2 Location of Perl
will stand in for whatever method works on your system. You are
advised to use a specific path if you care about a specific version.
- #!/usr/local/bin/perl5.00554
+ #!/usr/local/bin/perl5.14
or if you just want to be running at least version, place a statement
like this at the top of your program:
- use 5.005_54;
+ use 5.014;
=head2 Command Switches
X<perl, command switches> X<command switches>
specifies the input record separator (C<$/>) as an octal or
hexadecimal number. If there are no digits, the null character is the
separator. Other switches may precede or follow the digits. For
-example, if you have a version of B<find> which can print filenames
+example, if you have a version of I<find> which can print filenames
terminated by the null character, you can say this:
find . -name '*.orig' -print0 | perl -n0e unlink
The special value 00 will cause Perl to slurp files in paragraph mode.
-The value 0777 will cause Perl to slurp files whole because there is no
-legal byte with that value.
+Any value 0400 or above will cause Perl to slurp files whole, but by convention
+the value 0777 is the one normally used for this purpose.
-If you want to specify any Unicode character, use the hexadecimal
-format: C<-0xHHH...>, where the C<H> are valid hexadecimal digits.
-(This means that you cannot use the C<-x> with a directory name that
-consists of hexadecimal digits.)
+You can also specify the separator character using hexadecimal notation:
+B<-0xI<HHH...>>, where the C<I<H>> are valid hexadecimal digits. Unlike
+the octal form, this one may be used to specify any Unicode character, even
+those beyond 0xFF. So if you I<really> want a record separator of 0777,
+specify it as B<-0x1FF>. (This means that you cannot use the B<-x> option
+with a directory name that consists of hexadecimal digits, or else Perl
+will think you have specified a hex number to B<-0>.)
=item B<-a>
X<-a> X<autosplit>
=item B<-C [I<number/list>]>
X<-C>
-The C<-C> flag controls some of the Perl Unicode features.
+The B<-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
+As of 5.8.1, the B<-C> can be followed either by a number or a list
of option letters. The letters, their numeric values, and effects
are as follows; listing the letters is equal to summing the numbers.
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
+ 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.
+ 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 */"
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
+For example, B<-COE> and B<-C6> will both turn on UTF-8-ness on both
STDOUT and STDERR. Repeating letters is just redundant, not cumulative
nor toggling.
The C<io> options mean that any subsequent open() (or similar I/O
-operations) will have the C<:utf8> PerlIO layer implicitly applied
-to them, in other words, UTF-8 is expected from any input stream,
-and UTF-8 is produced to any output stream. This is just the default,
-with explicit layers in open() and with binmode() one can manipulate
-streams as usual.
+operations) in the current file scope will have the C<:utf8> PerlIO layer
+implicitly applied to them, in other words, UTF-8 is expected from any
+input stream, and UTF-8 is produced to any output stream. This is just
+the default, with explicit layers in open() and with binmode() one can
+manipulate streams as usual.
-C<-C> on its own (not followed by any number or option list), or the
+B<-C> on its own (not followed by any number or option list), or the
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
+same effect as B<-CSDL>. In other words, the standard I/O handles and
+the default C<open()> layer are UTF-8-fied I<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.
+(See L<perl581delta/UTF-8 no longer default under UTF-8 locales>.)
-You can use
C<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly
+You can use
B<-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>).
-(In Perls earlier than 5.8.1 the C<-C> switch was a Win32-only switch
+(In Perls earlier than 5.8.1 the B<-C> switch was a Win32-only switch
that enabled the use of Unicode-aware "wide system call" Win32 APIs.
This feature was practically unused, however, and the command line
switch was therefore "recycled".)
+B<Note:> Since perl 5.10.1, if the B<-C> option is used on the C<#!> 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<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.
+executing it. Actually, it I<will> execute and C<BEGIN>, C<UNITCHECK>,
+or C<CHECK> blocks and any C<use> statements: 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>
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]>
+=item B<-d:>I<MOD[=bar,baz]>
X<-d> X<-dt>
-=item B<-dt:>I<foo[=bar,baz]>
+=item B<-dt:>I<MOD[=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
-the program using the Devel::DProf profiler. As with the B<-M>
-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>.
+runs the program under the control of a debugging, profiling, or tracing
+module installed as C<Devel::I<MOD>>. E.g., B<-d:DProf> executes the
+program using the C<Devel::DProf> profiler. As with the B<-M> flag, options
+may be passed to the C<Devel::I<MOD>> package where they will be received
+and interpreted by the C<Devel::I<MOD>::import> routine. Again, like B<-M>,
+use -B<-d:-I<MOD>> to call C<Devel::I<MOD>::unimport> instead of import. 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>
16 o Method and overloading resolution
32 c String/numeric conversions
64 P Print profiling info, source file input state
- 128 m Memory allocation
+ 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 U Unofficial, User hacking (reserved for private, unreleased use)
+ 4096 U Unofficial, User hacking (reserved for private,
+ unreleased use)
8192 H Hash dump -- usurps values()
16384 X Scratchpad allocation
32768 D Cleaning up
- 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
+ 131072 T Tokenizing
+ 262144 R Include reference counts of dumped variables (eg when
+ using -Ds)
+ 524288 J show s,t,P-debug (don't Jump over) on 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
+ 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).
+executable (but see C<:opd> in L<Devel::Peek> or L<re/'debug' mode>
+which may change this).
See the F<INSTALL> file in the Perl source distribution
for how to do this. This flag is automatically set if you include B<-g>
option when C<Configure> asks you about optimizer/debugger flags.
optional features (in the main compilation unit). See L<feature>.
=item B<-f>
-X<-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
+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<$Config{sitelib}> is also determined in C code and not
+read from C<Config.pm>, which is not loaded.
+
+The code is executed I<very> early. For example, any changes made to
+C<@INC> will show up in the output of `perl -V`. Of course, C<END>
+blocks will be likewise executed very late.
+
+To determine at runtime if this capability has been compiled in your
+perl, you can check the value of C<$Config{usesitecustomize}>.
+
=item B<-F>I<pattern>
X<-F>
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'*' -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
+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
B<-M>I<module> executes C<use> I<module> C<;> before executing your
program. You can use quotes to add extra code after the module name,
-e.g., C<'-Mmodule qw(foo bar)'>.
+e.g., C<'-MI<MODULE> qw(foo bar)'>.
-If the first character after the B<-M> or B<-m> is a dash (C<->)
+If the first character after the B<-M> or B<-m> is a dash (B<->)
then the 'use' is replaced with 'no'.
A little builtin syntactic sugar means you can also say
-B<-mmodule=foo,bar> or B<-Mmodule=foo,bar> as a shortcut for
-C<'-Mmodule qw(foo bar)'>. This avoids the need to use quotes when
-importing symbols. The actual code generated by B<-Mmodule=foo,bar> is
+B<-mI<MODULE>=foo,bar> or B<-MI<MODULE>=foo,bar> as a shortcut for
+B<'-MI<MODULE> qw(foo bar)'>. This avoids the need to use quotes when
+importing symbols. The actual code generated by B<-MI<MODULE>=foo,bar> is
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.)
+A consequence of this is that B<-MI<MODULE>=number> never does a version check,
+unless C<I<MODULE>::import()> itself is set up to do a version check, which
+could happen for example if I<MODULE> inherits from L<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
+makes it iterate over filename arguments somewhat like I<sed -n> or
LINE:
while (<>) {
... # your program goes here
}
-Note that the lines are not printed by default. See B<-p> to have
+Note that the lines are not printed by default. See L</-p> to have
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.
+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
-This is faster than using the B<-exec> switch of B<find> because you don't
+This is faster than using the B<-exec> switch of I<find> because you don't
have to start a process on every filename found. It does suffer from
the bug of mishandling newlines in pathnames, which you can fix if
you follow the example under B<-0>.
C<BEGIN> and C<END> blocks may be used to capture control before or after
-the implicit program loop, just as in
B<awk>.
+the implicit program loop, just as in
I<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>:
+makes it iterate over filename arguments somewhat like I<sed>:
LINE:
overrides a B<-n> switch.
C<BEGIN> and C<END> blocks may be used to capture control before or after
-the implicit loop, just as in
B<awk>.
+the implicit loop, just as in
I<awk>.
=item B<-s>
X<-s>
#!/usr/bin/perl -s
if ($xyz) { print "$xyz\n" }
-Do note that a switch like B<--help> creates the variable ${-help}, which is not compliant
-with C<strict refs>. Also, when using this option on a script with
+Do note that a switch like B<--help> creates the variable C<${-help}>, which is not compliant
+with C<use 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).
+program unless the name of the program contains path separators.
On some platforms, this also makes Perl append suffixes to the
filename while searching for it. For example, on Win32 platforms,
the ".bat" and ".cmd" suffixes are appended if a lookup for the
original name fails, and if the name does not already end in one
-of those suffixes. If your Perl was compiled with DEBUGGING turned
-on, using the -Dp switch to Perl shows how the search progresses.
+of those suffixes. If your Perl was compiled with C<DEBUGGING> turned
+on, using the B<-Dp> switch to Perl shows how the search progresses.
-Typically this is used to emulate #! startup on platforms that don't
-support #!. Its also convenient when debugging a script that uses #!,
+Typically this is used to emulate C<#!> startup on platforms that don't
+support C<#!>. It's also convenient when debugging a script that uses C<#!>,
and is thus normally found by the shell's $PATH search mechanism.
This example works on many platforms that have a shell compatible with
lines and ignores them because the variable $running_under_some_shell
is never true. If the program will be interpreted by csh, you will need
to replace C<${1+"$@"}> with C<$*>, even though that doesn't understand
-embedded spaces (and such) in the argument list. To start up sh rather
-than csh, some systems may have to replace the #! line with a line
+embedded spaces (and such) in the argument list. To start up I<sh> rather
+than I<csh>, some systems may have to replace the C<#!> line with a line
containing just a colon, which will be politely ignored by Perl. Other
systems can't control that, and need a totally devious construct that
-will work under any of B<csh>, B<sh>, or Perl, such as the following:
+will work under any of I<csh>, I<sh>, or Perl, such as the following:
eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
& eval 'exec /usr/bin/perl -wS $0 $argv:q'
if $running_under_some_shell;
-If the filename supplied contains directory separators (i.e., is an
+If the filename supplied contains directory separators (and so is an
absolute or relative pathname), and if that file is not found,
platforms that append file extensions will do so and try to look
for the file with those extensions added, one by one.
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
+errors. These warnings can now be controlled normally with C<no warnings
qw(taint)>.
-B<NOTE: this is not a substitute for -T.> This is meant only to be
-used as a temporary development aid while securing legacy code:
-for real production code and for new secure code written from scratch
+B<Note: This is not a substitute for C<-T>!> This is meant to be
+used I<only> as a temporary development aid while securing legacy code:
+for real production code and for new secure code written from scratch,
always use the real B<-T>.
=item B<-T>
X<-T>
-forces "taint" checks to be turned on so you can test them. Ordinarily
+turns on "taint" so you can test them. Ordinarily
these checks are done only when running setuid or setgid. It's a
good idea to turn them on explicitly for programs that run on behalf
of someone else whom you might not necessarily trust, such as CGI
programs or any internet servers you might write in Perl. See
L<perlsec> for details. For security reasons, this option must be
seen by Perl quite early; usually this means it must appear early
-on the command line or in the #! line for systems which support
+on the command line or in the C<#!> line for systems which support
that construct.
=item B<-u>
X<-u>
-This obsolete switch causes Perl to dump core after compiling your
+This switch causes Perl to dump core after compiling your
program. You can then in theory take this core dump and turn it
-into an executable file by using the B<undump> program (not supplied).
+into an executable file by using the I<undump> program (not supplied).
This speeds startup at the expense of some disk space (which you
can minimize by stripping the executable). (Still, a "hello world"
executable comes out to about 200K on my machine.) If you want to
execute a portion of your program before dumping, use the dump()
-operator instead. Note: availability of B<undump> is platform
+operator instead. Note: availability of I<undump> is platform
specific and may not be available for a specific port of Perl.
=item B<-U>
X<-U>
allows Perl to do unsafe operations. Currently the only "unsafe"
-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.
+operations are attempting to unlink directories while running as superuser
+and running setuid programs with fatal taint checks turned into warnings.
+Note that warnings must be enabled along with this option to actually
+I<generate> the taint-check warnings.
=item B<-v>
X<-v>
=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
+with multiples when your C<I<configvar>> argument looks like a regex (has
non-letters). For example:
$ perl -V:libc
....
Additionally, extra colons can be used to control formatting. A
-trailing colon suppresses the linefeed and terminator ';', allowing
+trailing colon suppresses the linefeed and terminator ";", allowing
you to embed queries into shell commands. (mnemonic: PATH separator
-':'.)
+":".)
$ echo "compression-vars: " `perl -V:z.*: ` " are here !"
compression-vars: zcat='' zip='zip' are here !
-A leading colon removes the 'name=' part of the response, this allows
+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`
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.
+below, the C<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
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 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.
-
-This switch really just enables the internal C<$^W> variable. You
+mentioned only once and scalar variables used
+before being set; redefined subroutines; references to undefined
+filehandles; filehandles opened read-only that you are attempting
+to write on; values used as a number that don't I<look> like numbers;
+using an array as though it were a scalar; if your subroutines
+recurse more than 100 deep; and innumerable other things.
+
+This switch really just enables the global C<$^W> variable; normally,
+the lexically scoped C<use warnings> pragma is preferred. You
can disable or promote into fatal errors specific warnings using
C<__WARN__> hooks, as described in L<perlvar> and L<perlfunc/warn>.
-See also L<perldiag> and L<perltrap>. A new, fine-grained warning
+See also L<perldiag> and L<perltrap>. A fine-grained warning
facility is also available if you want to manipulate entire classes
of warnings; see L<warnings> or L<perllexwarn>.
=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
+text, such as in a mail message. Leading garbage will be
+discarded until the first line that starts with C<#!> 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!)">)
+will treat the C<#!> 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, not as line 100.
+This can be overridden by using the C<#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
-C<__END__> if there is trailing garbage to be ignored (the program
-can process any or all of the trailing garbage via the DATA filehandle
-if desired).
+C<__END__> if there is trailing garbage to be ignored; the program
+can process any or all of the trailing garbage via the C<DATA> filehandle
+if desired.
The directory, if specified, must appear immediately following the B<-x>
with no intervening whitespace.
=item HOME
X<HOME>
-Used if chdir has no argument.
+Used if C<chdir> has no argument.
=item LOGDIR
X<LOGDIR>
-Used if chdir has no argument and HOME is not set.
+Used if C<chdir> has no argument and HOME is not set.
=item PATH
X<PATH>
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 (this lookup
-being done at interpreter startup time.)
+locations are automatically included if they exist, with this lookup
+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
+(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>).
+-V:I<path_sep>>).
-When running taint checks (either because the program was running setuid
-or setgid, or the B<-T> or B<-t> switch was specified), neither variable
-is used. The program should instead say:
+When running taint checks, either because the program was running setuid or
+setgid, or the B<-T> or B<-t> switch was specified, neither PERL5LIB nor
+PERLLIB is consulted. 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<-[CDIMUdmtw]>
-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.
+Command-line options (switches). Switches in this variable are treated
+as if they were on every Perl command line. Only the B<-[CDIMUdmtwW]>
+switches are allowed. When running taint checks (either because the
+program was running setuid or setgid, or because the B<-T> or B<-t>
+switch was used), this variable is ignored. If PERL5OPT begins with
+B<-T>, tainting will be enabled and subsequent options ignored. If
+PERL5OPT begins with B<-t>, tainting will be enabled, a writable dot
+removed from @INC, and subsequent options honored.
=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.
+to use PerlIO system for IO (the default) these layers affect Perl's IO.
-It is conventional to start layer names with a colon e.g. C<:perlio> to
-emphasise their similarity to variable "attributes". But the code that parses
-layer specification strings (which is also used to decode the PERLIO
-environment variable) treats the colon as a separator.
+It is conventional to start layer names with a colon (for example, C<:perlio>) to
+emphasize their similarity to variable "attributes". But the code that parses
+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 the default set of layers for
-your platform, for example C<:unix:perlio> on UNIX-like systems
+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
-IO in order to load them!. See L<"open pragma"|open> for how to add external
+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 C<:encoding()>) need
+IO in order to load them! See L<"open pragma"|open> for how to add external
encodings as defaults.
-The layers that it makes sense to include in the PERLIO environment
-variable are briefly summari
sed below. For more details see L<PerlIO>.
+Layers it makes sense to include in the PERLIO environment
+variable are briefly summari
zed 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.
+A pseudolayer that turns the C<:utf8> flag I<off> 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 which does CRLF to "\n" translation distinguishing "text" and
+A layer which does CRLF to C<"\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
+A layer that implements "reading" of files by using I<mmap>(2) to
+make an entire file appear in the process's address space, and then
using that as PerlIO's "buffer".
=item :perlio
X<:perlio>
-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>).
+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 nitroglycerin.
+Use with the same care as is reserved for nitroglycerine.
=item :raw
X<: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.
+pass each byte as-is without translation. In particular, both CRLF
+translation and intuiting C<:utf8> from the locale are disabled.
-Unlike in the earlier versions of Perl C<:raw> is I<not>
-just the inverse of C<:crlf> - other layers which would affect the
+Unlike in 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"
+This layer provides a PerlIO interface by wrapping system's ANSI C "stdio"
library calls. The layer provides both buffering and IO.
-Note that C<:stdio> layer does I<not> do CRLF translation even if that
-is platforms normal behaviour. You will need a C<:crlf> layer above it
+Note that the C<:stdio> layer does I<not> do CRLF translation even if that
+is the platform's normal behaviour. You will need a C<:crlf> layer above it
to do that.
=item :unix
X<:unix>
-Low level layer which calls C<read>, C<write> and C<lseek> etc.
+Low-level layer that calls C<read>, C<write>, C<lseek>, etc.
=item :utf8
X<:utf8>
-A pseudolayer that turns on a flag on the layer below to tell perl
+A pseudolayer that enables a flag in the layer below to tell Perl
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
+already in valid utf8 form. B<WARNING: It does not check for validity and as such
+should be handled with extreme caution for input, because security violations
+can occur with non-shortest UTF-8 encodings, etc.> 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
-buggy in this release.
+rather than a Unix-like numeric file descriptor layer. Known to be
+buggy in this release (5.14).
=back
-On all platforms the default set of layers should give acceptable results.
+The default set of layers should give acceptable results on all platforms
-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"
+For Unix platforms that will be the equivalent of "unix perlio" or "stdio".
+Configure is set up to prefer the "stdio" implementation if the system's library
+provides for fast access to the buffer; otherwise, it uses the "unix perlio"
implementation.
-On Win32 the default in this release is "unix crlf". Win32's "stdio"
-has a number of bugs/mis-features for perl IO which are somewhat
-C compiler vendor/version dependent. Using our own C<crlf> layer as
-the buffer avoids those issues and makes things more uniform.
-The C<crlf> layer provides CRLF to/from "\n" conversion as well as
-buffering.
+On Win32 the default in this release (5.14) is "unix crlf". Win32's "stdio"
+has a number of bugs/mis-features for Perl IO which are somewhat depending
+on the version and vendor of the C compiler. Using our own C<crlf> layer as
+the buffer avoids those issues and makes things more uniform. The C<crlf>
+layer provides CRLF conversion as well as buffering.
-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 be
-the default under Win32.
+This release (5.14) uses C<unix> as the bottom layer on Win32, and so still
+uses the C compiler's numeric file descriptor routines. There is an
+experimental native C<win32> layer, which is expected to be enhanced and
+should eventually become the default under Win32.
-The PERLIO environment variable is completely ignored when perl
+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:
+If set to the name of a file or device, certain operations of PerlIO
+subsystem will be logged to that file, which is opened in append mode.
+Typical uses are in Unix:
- PERLIO_DEBUG=/dev/tty perl script ...
+ % env PERLIO_DEBUG=/dev/tty perl script ...
-and Win32 approximate equivalent:
+and under Win32, the approximately equivalent:
- set PERLIO_DEBUG=CON
+ > set PERLIO_DEBUG=CON
perl script ...
This functionality is disabled for setuid scripts and for scripts run
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
+The PERLLIB environment variable is completely ignored when Perl
is run in taint mode.
=item PERL5DB
The command used to load the debugger code. The default is:
- BEGIN { require 'perl5db.pl' }
+ BEGIN { require "perl5db.pl" }
-The PERL5DB environment variable only used when perl is started with
+The PERL5DB environment variable is only used when Perl is started with
a bare B<-d> switch.
=item PERL5DB_THREADED
=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>
-on WindowsNT and C<command.com /c> on Windows95. The value is considered
-to be space-separated. Precede any character that needs to be protected
-(like a space or backslash) with a backslash.
+On Win32 ports only, 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> on WindowsNT and C<command.com /c> on Windows95. The
+value is considered space-separated. Precede any character that
+needs to be protected, like a space or backslash, with another backslash.
Note that Perl doesn't use COMSPEC for this purpose because
COMSPEC has a high degree of variability among users, leading to
-portability concerns. Besides, perl can use a shell that may not be
+portability concerns. Besides, Perl can use a shell that may not be
fit for interactive use, and setting COMSPEC to such a shell may
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.
+Set to 1 to allow the use of non-IFS compatible LSPs (Layered Service Providers).
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
+cause problems if you have a firewall such as I<McAfee Guardian>, which requires
+that all applications use its LSP but 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).
+first suitable LSP enumerated in the catalog, which keeps I<McAfee Guardian>
+happy--and in that particular case Perl still works too because I<McAfee
+Guardian>'s LSP actually plays 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').
-If set, this causes memory statistics to be dumped after execution. If set
-to an integer greater than one, also causes memory statistics to be dumped
+Relevant only if Perl is compiled with the C<malloc> included with the Perl
+distribution; that is, if C<perl -V:d_mymalloc> is "define".
+
+If set, this dumps out memory statistics after execution. If set
+to an integer greater than one, also dumps out memory statistics
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.
+Relevant only if your Perl executable was built with B<-DDEBUGGING>,
+this controls the behaviour of global destruction of objects and other
+references. See L<perlhacktips/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
+Set to
C<"1"> to have Perl resolve I<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.
+extensions, as it ensures that you get an error on misspelled function
+names even if the test suite doesn't call them.
=item PERL_ENCODING
X<PERL_ENCODING>
-If using the C<encoding> pragma without an explicit encoding name, the
+If using the C<use 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
-exactly the same order as 5.8.0). "Pre-5.8.1" means, among other
+(Since Perl 5.8.1.) Used to randomize Perl's internal hash function.
+To emulate the pre-5.8.1 behaviour, set to an integer; C<"0"> means
+exactly the same order as in 5.8.0. "Pre-5.8.1" means, among other
things, that hash keys will always have the same ordering between
-different runs of perl.
+different runs of Perl.
-Most hashes return elements in the same order as Perl 5.8.0 by default.
+Most hashes by default return elements in the same order as in Perl 5.8.0.
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
-behaviour is B<not> to randomise unless the PERL_HASH_SEED is set.
+The default behaviour is to randomize unless the PERL_HASH_SEED is set.
+If Perl has been compiled with B<-DUSE_HASH_SEED_EXPLICIT>, the default
+behaviour is I<not> to randomize 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.
-B<Please note that the hash seed is sensitive information>. Hashes are
+B<PLEASE NOTE: 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
+code. By manually setting a seed, this protection may be partially or
completely lost.
See L<perlsec/"Algorithmic Complexity Attacks"> and
=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
+(Since Perl 5.8.1.) Set to C<"1"> 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.
+behaviour caused by hash randomization.
-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,
+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>.
+See also hash_seed() in L<Hash::Util>.
+
+=item PERL_MEM_LOG
+X<PERL_MEM_LOG>
+
+If your Perl was configured with B<-Accflags=-DPERL_MEM_LOG>, setting
+the environment variable C<PERL_MEM_LOG> enables logging debug
+messages. The value has the form C<< <I<number>>[m][s][t] >>, where
+C<I<number>> is the file descriptor number you want to write to (2 is
+default), 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_MEM_LOG=1mst> logs all
+information to stdout. You can write to other opened file descriptors
+in a variety of ways:
+
+ $ 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
+A translation-concealed rooted logical name that contains Perl and the
logical device for the @INC path on VMS only. Other logical names that
-affect perl on VMS include PERLSHR, PERL_ENV_TABLES, and
-SYS$TIMEZONE_DIFFERENTIAL but are optional and discussed further in
+affect Perl on VMS include PERLSHR, PERL_ENV_TABLES, and
+SYS$TIMEZONE_DIFFERENTIAL, but are optional and discussed further in
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)">.
+Available in Perls 5.8.1 and later. If set to C<"unsafe">, the pre-Perl-5.8.0
+signal behaviour (which is immediate but unsafe) is restored. If set
+to C<safe>, then safe (but deferred) signals are used. 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>
+your shell before starting Perl). See the description of the B<-C>
switch for more information.
=item SYS$LOGIN (specific to the VMS port)
=back
Perl also has environment variables that control how Perl handles data
-specific to particular natural languages. See L<perllocale>.
-
-Apart from these, Perl uses no other environment variables, except
-to make them available to the program being executed, and to child
-processes. However, programs running setuid would do well to execute
-the following lines before doing anything else, just to keep people
-honest:
-
- $ENV{PATH} = '/bin:/usr/bin'; # or whatever you need
- $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
+specific to particular natural languages; see L<perllocale>.
+
+Perl and its various modules and components, including its test frameworks,
+may sometimes make use of certain other environment variables. Some of
+these are specific to a particular platform. Please consult the
+appropriate module documentation and any documentation for your platform
+(like L<perlsolaris>, L<perllinux>, L<perlmacosx>, L<perlwin32>, etc) for
+variables peculiar to those specific situations.
+
+Perl makes all environment variables available to the program being
+executed, and passes these along to any child processes it starts.
+However, programs running setuid would do well to execute the following
+lines before doing anything else, just to keep people honest:
+
+ $ENV{PATH} = "/bin:/usr/bin"; # or whatever you need
+ $ENV{SHELL} = "/bin/sh" if exists $ENV{SHELL};
delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};
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