# ABSTRACT: A collection of Perl idioms or short pieces of Perl code
# PODNAME: perlsnippets

__END__

=pod

=encoding UTF-8

=head1 NAME

perlsnippets - A collection of Perl idioms or short pieces of Perl code

=head1 VERSION

This document describes version 0.003 of perlsnippets (from Perl distribution perlsnippets), released on 2019-06-04.

=head1 DESCRIPTION

This distribution catalogs (in its POD pages) various idioms or short pieces of
code that a Perl programmer usually uses. You can also copy-paste them to your
code.

The pieces of code are often too small to refactor into modules, or sometimes
they have been refactored as modules but you still want to "inline" them to
avoid adding a dependency. The pieces of code are often Perl idioms (patterns of
code that are specific to Perl programming), but not always.

=head1 ARY (Arrays)

=head1 ARY/SORT (Arrays / Sorting Arrays)

=head2 ARY/SORT/1 (Schwartzian transform)

 my @sorted = map  { $_->[0] }
              sort { $a->[1] <=> $b->[1] }
              map  { [$_, gen_key_for($_)] }
              @ary;

This is the infamous Schwartzian transform named after Randal Schwartz who
popularized it during the early days of Perl 5 in 1994. Basically, it's a
one-statement way to sort an array using a key. Examples of functions to
generate a key: C<length($_)> (to sort by string length), C<lc($_)> (to do
case-insensitive sorting).

Related documentation: L<https://en.wikipedia.org/wiki/Schwartzian_transform>

=head1 HASH (Hashes)

=head1 IO (I/O)

=head1 IO/FILE (I/O / File I/O)

=head2 IO/FILE/1 (Slurping a file content into a string)

 my $content = do { local $/; <$fh> };

The above snippet slurps the whole file (which has been opened with filehandle
C<$fh>) into memory (scalar variable). The C<do {}> block localizes the effect
of C<$/>. If you start from a filename and want to open it first:

=head2 IO/FILE/2 (Slurping a file content into a string)

 my $content = do { local $/; open my $fh, "<", $filename; <$fh> };

=head2 IO/FILE/3 (Slurping a file content into array of strings)

 my @lines = do { local $/; open my $fh, "<", $filename; <$fh> };

Like the previous snippet but you get the content as an array of lines. Each
line still has their terminating newlines.

=head2 IO/FILE/4 (Slurping a file content into array of strings)

 chomp(my @lines = do { local $/; open my $fh, "<", $filename; <$fh> });

Like the previous snippet, but the lines no longer contain newlines because they
are C<chomp()>-ed.

Related modules: L<File::Slurper>.

Related documentation: C<$/> in L<perlvar>.

=head1 MOD (Modules)

=head2 MOD/LOAD/1 (Requiring a module by name from variable)

 { (my $mod_pm = "$mod.pm") =~ s!::!/!g; require $mod_pm }

You have a module name in C<$mod> (e.g. C<"Foo::Bar">) and want to
load/C<require> it. You cannot just use C<require $mod> because require expects
its non-bareware argument to be in the form of C<"Foo/Bar.pm">. So the above
snippet converts C<$mod> to that form.

This is safer than C<eval "use $mod"> or C<eval "require $mod"> which work but
necessitates you to check that $mod does not contain arbitrary and dangerous
code.

Related modules: L<Module::Load>

Related documentation: C<require> in L<perlfunc>.

=head2 MOD/LOAD/2 (Requiring a module and importing from it)

 require Foo::Bar; Foo::Bar->import("baz", "qux");

The above snippet loads C<Foo::Bar> module and imports things from the module.
It is the run-time equivalent of C<< use Foo::Bar "baz", "qux"; >>. C<< require
Foo::Bar; >> itself is the run-time equivalent of C<< use Foo::Bar (); >>, i.e.
loading a module without importing anything from it.

=head1 PROC (Process Management)

=head1 PROC/CHLD (Process / Child Process)

Some bit-fiddling and logic is needed to extract exit code from C<$?>
(C<$CHILD_ERROR>). L<Process::Status> makes things easier by presenting you with
an object that you can query, but if you just want an exit code:

=head2 PROC/CHLD/1 (Extract information from $?)

 my ($exit_code, $signal, $core_dump) = ($? < 0 ? $? : $? >> 8, $? & 127, $? & 128);

This snippet extracts all the information contained in C<$?>: exit code (which
can be -1 to mean there is no child process being created due to an execution
error, e.g. C<system "non-existent-command">), what signal the child process
dies from, and whether the child process dumps core.

=head2 PROC/CHLD/2 (Extract exit code from $?)

 my $exit_code = $? < 0 ? $? : $? >> 8.

This snippets just extracts the exit code of child process (which can be -1 to
mean that there is no child process being created due to an execution error,
e.g. C<system "non-existent-command">).

Related modules: L<Process::Status>, L<Proc::ChildError>.

Related documentation: C<$?> in L<perlvar>.

=head1 OBJ (Objects)

=head1 REF (References)

=head1 SUB (Subroutines)

=head1 SUB/ARG (Subroutines / Subroutine Arguments)

=head1 HOMEPAGE

Please visit the project's homepage at L<https://metacpan.org/release/perlsnippets>.

=head1 SOURCE

Source repository is at L<https://github.com/perlancar/perl-perlsnippets>.

=head1 BUGS

Please report any bugs or feature requests on the bugtracker website L<https://rt.cpan.org/Public/Dist/Display.html?Name=perlsnippets>

When submitting a bug or request, please include a test-file or a
patch to an existing test-file that illustrates the bug or desired
feature.

=head1 SEE ALSO

L<Common Perl idioms (2004)|https://www.perlmonks.org/?node_id=376948>

The Idioms subchapter in the Modern Perl book. L<http://modernperlbooks.com/>

L<perlsecret>

=head1 AUTHOR

perlancar <perlancar@cpan.org>

=head1 COPYRIGHT AND LICENSE

This software is copyright (c) 2019 by perlancar@cpan.org.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

=cut
