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
+a specific version of Perl, say, perl5.14.1, you should place
that directly in the C<#!> line's path.
-If the C<#!> line does not contain the word "perl", 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.
+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
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
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>
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 */"
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 B<-C0> (or C<"0"> for C<PERL_UNICODE>) to explicitly
disable all the above Unicode features.
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
+ 65536 S Op slab allocation
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
+ 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
+ 33554432 B dump suBroutine definitions, including special Blocks
+ like BEGIN
All these flags require B<-DDEBUGGING> when you compile the Perl
executable (but see C<:opd> in L<Devel::Peek> or L<re/'debug' mode>
modify the name of the old file to make a backup copy, following these
rules:
-If no extension is supplied, no backup is made and the current file is
-overwritten.
+If no extension is supplied, and your system supports it, the original
+I<file> is kept open without a name while the output is redirected to
+a new file with the original I<filename>. When perl exits, cleanly or not,
+the original I<file> is unlinked.
If the extension doesn't contain a C<*>, then it is appended to the
end of the current filename as a suffix. If the extension does
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
... # 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.
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, with this lookup
-done at interpreter startup time.
+directory. Any architecture-specific and version-specific directories,
+such as F<version/archname/>, F<version/>, or F<archname/> under the
+specified locations are automatically included if they exist, with this
+lookup done at interpreter startup time. In addition, any directories
+matching the entries in C<$Config{inc_version_list}> are added.
+(These typically would be for older compatible perl versions installed
+in the same directory tree.)
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
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
+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.
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
+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
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
+IO in order to load them! See L<"open pragma"|open> for how to add external
encodings as defaults.
Layers it makes sense to include in the PERLIO environment
X<PERLIO_DEBUG>
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
+subsystem will be logged to that file, which is opened in append mode.
Typical uses are in Unix:
% env PERLIO_DEBUG=/dev/tty perl script ...
=item PERL_HASH_SEED
X<PERL_HASH_SEED>
-(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.
+(Since Perl 5.8.1, new semantics in Perl 5.18.0) Used to override
+the randomization of Perl's internal hash function. The value is expressed
+in hexadecimal, and may include a leading 0x. Truncated patterns
+are treated as though they are suffixed with sufficient 0's as required.
-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 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
-the pseudorandom seed supplied by the operating system and libraries.
+If the option is provided, and C<PERL_PERTURB_KEYS> is NOT set, then
+a value of '0' implies C<PERL_PERTURB_KEYS=0> and any other value
+implies C<PERL_PERTURB_KEYS=2>.
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
completely lost.
-See L<perlsec/"Algorithmic Complexity Attacks"> and
+See L<perlsec/"Algorithmic Complexity Attacks"> and L</PERL_PERTURB_KEYS>
L</PERL_HASH_SEED_DEBUG> for more information.
+=item PERL_PERTURB_KEYS
+X<PERL_PERTURB_KEYS>
+
+(Since Perl 5.18.0) Set to C<"0"> or C<"NO"> then traversing keys
+will be repeatable from run to run for the same PERL_HASH_SEED.
+Insertion into a hash will not change the order, except to provide
+for more space in the hash. When combined with setting PERL_HASH_SEED
+this mode is as close to pre 5.18 behavior as you can get.
+
+When set to C<"1"> or C<"RANDOM"> then traversing keys will be randomized.
+Every time a hash is inserted into the key order will change in a random
+fashion. The order may not be repeatable in a following program run
+even if the PERL_HASH_SEED has been specified. This is the default
+mode for perl.
+
+When set to C<"2"> or C<"DETERMINISTIC"> then inserting keys into a hash
+will cause the key order to change, but in a way that is repeatable
+from program run to program run.
+
+B<NOTE:> Use of this option is considered insecure, and is intended only
+for debugging non-deterministic behavior in Perl's hash function. Do
+not use it in production.
+
+See L<perlsec/"Algorithmic Complexity Attacks"> and L</PERL_HASH_SEED>
+and L</PERL_HASH_SEED_DEBUG> for more information. You can get and set the
+key traversal mask for a specific hash by using the C<hash_traversal_mask()>
+function from L<Hash::Util>.
+
=item PERL_HASH_SEED_DEBUG
X<PERL_HASH_SEED_DEBUG>
-(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
-behaviour caused by hash randomization.
+(Since Perl 5.8.1.) Set to C<"1"> to display (to STDERR) information
+about the hash function, seed, and what type of key traversal
+randomization is in effect at the beginning of execution. This, combined
+with L</PERL_HASH_SEED> and L</PERL_PERTURB_KEYS> is intended to aid in
+debugging nondeterministic behaviour caused by hash randomization.
+
+B<Note> that any information about the hash function, especially the hash
+seed is B<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 C<hash_seed()> and
+C<key_traversal_mask()> in L<Hash::Util>.
+
+An example output might be:
-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() in L<Hash::Util>.
+ HASH_FUNCTION = ONE_AT_A_TIME_HARD HASH_SEED = 0x652e9b9349a7a032 PERTURB_KEYS = 1 (RANDOM)
=item PERL_MEM_LOG
X<PERL_MEM_LOG>
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