Hidden features of Perl?

Answer 1

The goatse operator*:

$_ = "foo bar";
my $count =()= /[aeiou]/g; #3

or

sub foo {
    return @_;
}

$count =()= foo(qw/a b c d/); #4

It works because list assignment in scalar context yields the number of elements in the list being assigned.

* Note, not really an operator

Answer 2

As Perl has almost all "esoteric" parts from the other lists, I'll tell you the one thing that Perl can't:

The one thing Perl can't do is have bare arbitrary URLs in your code, because the // operator is used for regular expressions.

Just in case it wasn't obvious to you what features Perl offers, here's a selective list of the maybe not totally obvious entries:

Duff's Device - in Perl

Portability and Standardness - There are likely more computers with Perl than with a C compiler

A file/path manipulation class - File::Find works on even more operating systems than .Net does

Quotes for whitespace delimited lists and strings - Perl allows you to choose almost arbitrary quotes for your list and string delimiters

Aliasable namespaces - Perl has these through glob assignments:

*My::Namespace:: = \%Your::Namespace

Static initializers - Perl can run code in almost every phase of compilation and object instantiation, from BEGIN (code parse) to CHECK (after code parse) to import (at module import) to new (object instantiation) to DESTROY (object destruction) to END (program exit)

Functions are First Class citizens - just like in Perl

Block scope and closure - Perl has both

Calling methods and accessors indirectly through a variable - Perl does that too:

my $method = 'foo';
my $obj = My::Class->new();
$obj->$method( 'baz' ); # calls $obj->foo( 'baz' )

Defining methods through code - Perl allows that too:

*foo = sub { print "Hello world" };

Pervasive online documentation - Perl documentation is online and likely on your system too

Magic methods that get called whenever you call a "nonexisting" function - Perl implements that in the AUTOLOAD function

Symbolic references - you are well advised to stay away from these. They will eat your children. But of course, Perl allows you to offer your children to blood-thirsty demons.

One line value swapping - Perl allows list assignment

Ability to replace even core functions with your own functionality

use subs 'unlink'; 
sub unlink { print 'No.' }

or

BEGIN{
    *CORE::GLOBAL::unlink = sub {print 'no'}
};

unlink($_) for @ARGV

Answer 3

The quoteword operator is one of my favourite things. Compare:

my @list = ('abc', 'def', 'ghi', 'jkl');

and

my @list = qw(abc def ghi jkl);

Much less noise, easier on the eye. Another really nice thing about Perl, that one really misses when writing SQL, is that a trailing comma is legal:

print 1, 2, 3, ;

That looks odd, but not if you indent the code another way:

print
    results_of_foo(),
    results_of_xyzzy(),
    results_of_quux(),
    ;

Adding an additional argument to the function call does not require you to fiddle around with commas on previous or trailing lines. The single line change has no impact on its surrounding lines.

This makes it very pleasant to work with variadic functions. This is perhaps one of the most under-rated features of Perl.

Answer 4

This is a meta-answer, but the Perl Tips archives contain all sorts of interesting tricks that can be done with Perl. The archive of previous tips is on-line for browsing, and can be subscribed to via mailing list or atom feed.

Some of my favourite tips include building executables with PAR, using autodie to throw exceptions automatically, and the use of the switch and smart-match constructs in Perl 5.10.

Disclosure: I'm one of the authors and maintainers of Perl Tips, so I obviously think very highly of them. ;)

Answer 5

rename("$_.part", $_) for "data.txt";

renames data.txt.part to data.txt without having to repeat myself.

Answer 6

Not really hidden, but many every day Perl programmers don't know about CPAN. This especially applies to people who aren't full time programmers or don't program in Perl full time.