$ perl -e 'print join(", ",qw(1 3 6 2));'
1, 3, 6, 2
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[jeroen@rulffk]  perl -e 'print join(", ",(1 3 6 2));'
Number found where operator expected at -e line 1, near "1 3"
    (Missing operator before  3?)
syntax error at -e line 1, near "1 3"
Number found where operator expected at -e line 1, near "3 6"
    (Missing operator before  6?)
Number found where operator expected at -e line 1, near "6 2"
    (Missing operator before  2?)
Execution of -e aborted due to compilation errors.
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Jeroen
"We are not alone"(FZ)

Ok ! thanks for the answer ! I've totally miss the separator problem !

So, if I've understood

use Digest::MD5  qw(md5 md5_hex md5_base64);

is exactly the same as

use Digest::MD5(md5,md5_hex,md5_base64);

Well, if you add a space after MD5 ;-).

But that's not the whole thing. From the manpage:

=item qw/STRING/

Returns a list of the words extracted out of STRING, using embedded
whitespace as the word delimiters.  It is exactly equivalent to

    split(' ', q/STRING/);

Some frequently seen examples:

    use POSIX qw( setlocale localeconv )
    @EXPORT = qw( foo bar baz );

A common mistake is to try to separate the words with comma or to put
comments into a multi-line qw-string.  For this reason the C<-w>
switch produce warnings if the STRING contains the "," or the "#"
character.
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So, there is a difference, although small.

Jeroen
"We are not alone"(FZ)

No.

Using strict would point out the error for you.

qw() is great for defining lists, especially of single-word strings, because you don't have to quote and comma delimit the list. It's usefulness becomes even more apparent when you have rather complicated code and if you can reduce punctuation you'll save on aspirin bills.

#!perl -w

use strict;

use vars qw(@array);
# same as: use vars '@array';

BEGIN {
  # the use vars below happens at compile time,
  # so @array must be set at compile time
  @array = ('$scalar', '%hash');
}

use vars (@array);
# $scalar and %hash are now declared

$scalar = 7;
%hash = (key => 'value');
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