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<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal>] ]>
+ 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<-S> ]>
S<[ B<-x>[I<dir>] ]>
S<[ B<-i>[I<extension>] ]>
S<[ B<-e> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>
- S<[ B<-C [I<number/list>] >]> ]>
+ S<[ B<-A [I<assertions>] >]>
+ S<[ B<-C [I<number/list>] >]>
=head1 DESCRIPTION
=item MS-DOS
Create a batch file to run your program, and codify it in
-C<ALTERNATIVE_SHEBANG> (see the F<dosish.h> file in the source
+C<ALTERNATE_SHEBANG> (see the F<dosish.h> file in the source
distribution for more information).
=item Win95/NT
=over 5
-=item B<-0>[I<digits>]
+=item B<-0>[I<octal/hexadecimal>]
-specifies the input record separator (C<$/>) as an octal number. If there are
-no digits, the null character is the separator. Other switches may
-precede or follow the digits. For example, if you have a version of
-B<find> which can print filenames terminated by the null character, you
-can say this:
+specifies the input record separator (C<$/>) 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
+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 character with that value.
+legal byte with that value.
+
+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.)
+
+=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>
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
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
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
+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> UTF-8 behaviour of Perl 5.8.0.
+I<implicit> (and problematic) UTF-8 behaviour of Perl 5.8.0.
-You can use C<-C0> to explicitly disable all the above Unicode features.
-
-See L<perlfunc/open>, and L<open> for more information.
+You can use C<-C0> (or C<"0"> for $ENV{PERL_UNICODE}) to explicitly
+disable all the above Unicode features.
The read-only magic variable C<${^UNICODE}> reflects the numeric value
-of this setting, see L<perlvar/"${^UNICODE}">.
+of this setting. This is 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
that enabled the use of Unicode-aware "wide system call" Win32 APIs.
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
=item PERL5LIB
-A colon-separated list of directories in which to look for Perl library
+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.
+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.
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>.
+
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
=item :bytes
-Turns I<off> the C<:utf8> flag for the layer below.
-Unlikely to be useful in global PERLIO environment variable.
+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
-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.
+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.
=item :mmap
C<:perlio> will insert a C<:unix> layer below itself to do low level IO.
+=item :pop
+
+An experimental pseudolayer that removes the topmost layer.
+Use with the same care as is reserved for nitroglyserin.
+
=item :raw
-Applying the <:raw> layer is equivalent to calling C<binmode($fh)>.
-It makes the stream pass each byte as-is without any translation.
-In particular CRLF translation, and/or :utf8 inuited from locale
-are disabled.
+A pseudolayer that manipulates other layers. Applying the <:raw>
+layer is equivalent to calling C<binmode($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.
=item :utf8
-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.)
+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.)
=item :win32
=item PERLLIB
-A colon-separated list of directories in which to look for Perl library
+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 PERL5SHELL (specific to the Win32 port)
May be set to an alternative shell that perl must use internally for
-executing "backtick" commands or system(). Default is C<cmd.exe /x/c>
+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.
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
+
+(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.
+
+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.
+
+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
+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
+
+(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.
+
+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)
A translation concealed rooted logical name that contains perl and the
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 signals are used.
+C<safe> the safe (or deferred) signals are used.
+See L<perlipc/"Deferred Signals (Safe signals)">.
=item PERL_UNICODE
-Equivalent to the B<-C> command-line switch.
+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
+"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)
https://perl5.git.perl.org / perl5.git / blobdiff