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" nor the word "indir"
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>
An alternate delimiter may be specified using B<-F>.
+B<-a> implicitly sets B<-n>.
+
=item B<-C [I<number/list>]>
X<-C>
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)
=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. You can't use literal whitespace in the pattern.
+specifies the pattern to split on for B<-a>. The pattern may be
+surrounded by C<//>, C<"">, or C<''>, otherwise it will be put in single
+quotes. You can't use literal whitespace in the pattern.
+
+B<-F> implicitly sets both B<-a> and B<-n>.
=item B<-h>
X<-h>
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
specified in the extension then it will skip that file and continue on
with the next one (if it exists).
-For a discussion of issues surrounding file permissions and B<-i>,
-see L<perlfaq5/Why does Perl let me delete read-only files? Why does -i clobber protected files? Isn't this a bug in Perl?>.
+For a discussion of issues surrounding file permissions and B<-i>, see
+L<perlfaq5/Why does Perl let me delete read-only files? Why does -i clobber
+protected files? Isn't this a bug in Perl?>.
You cannot use B<-i> to create directories or to strip extensions from
files.
#!/usr/bin/perl -s
if ($xyz) { print "$xyz\n" }
-Do note that a switch like B<--help> creates the variable C<${-help}>, which is not compliant
-with C<use strict "refs">. Also, when using this option on a script with
-warnings enabled you may get a lot of spurious "used only once" warnings.
+Do note that a switch like B<--help> creates the variable C<${-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>
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.
-
-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.
+(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.
-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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