There are quite a few modules to launch external process (mostly under IPC::), but operator qx{} (see perlop) or open(my $fh, '-|', ...) might be all you need.

Mind you, it would be silly to execute cat instead of just opening the file(s).

generic module to catch the output of the common UNIX/Linux commands ... into Perl data structures such as hashes

Others have already made a couple of suggestions, so let me just focus on the generic aspect of capturing and parsing the output of arbitrary Unix commands.

To have a generic solution, such a module would have to devise some mini (or rather maxi) language that allows you to specify how the respective output is to be parsed and split up into Perl data structures.  This would likely turn out to be so complex that one might as well just write the few lines of Perl that will achieve the same...  For example, the code to capture and split up the output of ls -l might look something like this:

#!/usr/bin/perl
use strict;
use warnings;

my $cmd = 'ls -l [0-9]*.pl';

my %fileinfo;

open my $capt, "$cmd |" or die "Couldn't run shell/'$cmd': $!";
while (<$capt>) {
    my ($mode, $links, $owner, $group, $size, $date, $time, $fname) = 
+split;
    my ($type, $perm) = unpack "aa*", $mode;
    $fileinfo{$fname} = {
        SIZE  => $size,
        DATE  => "$date $time",
        OWNER => $owner,
        PERM  => $perm,
    } if $type eq '-';
}

use Data::Dumper;
$Data::Dumper::Indent   = 1;
$Data::Dumper::Sortkeys = 1;

print Dumper \%fileinfo;

__END__
$VAR1 = {
  ...

  '828461.pl' => {
    'DATE' => '2010-03-13 21:20',
    'OWNER' => 'almut',
    'PERM' => 'rwxr--r--',
    'SIZE' => '502'
  },
  '828472.pl' => {
    'DATE' => '2010-03-13 20:31',
    'OWNER' => 'almut',
    'PERM' => 'rwxr--r--',
    'SIZE' => '83'
  },
  '828529.pl' => {
    'DATE' => '2010-03-14 12:52',
    'OWNER' => 'almut',
    'PERM' => 'rwxr--r--',
    'SIZE' => '807'
  }
};
[download]

OTOH, as Corion has already hinted at, Perl comes with all kinds of nifty stuff that often allows you get away without having to invoke external Unix commands.  In other words, the following would achieve almost the same as the above script (translating '755' ($mode) into 'rwxr-xr-x' etc. is left as an exercise for the reader):

#!/usr/bin/perl
use strict;
use warnings;
use POSIX qw(strftime);  # for date formatting

my %fileinfo;

for my $fname (glob "[0-9]*.pl") {
    my ($mode, $uid, $size, $mtime) = (stat $fname)[2,4,7,9];
    $fileinfo{$fname} = {
        SIZE  => $size,
        DATE  => strftime("%Y-%m-%d %H:%M", localtime($mtime)),
        OWNER => scalar getpwuid($uid),
        PERM  => sprintf("%o", $mode & 07777),
    } if -f _;
}
# ...dump %fileinfo
[download]

Of course, if you need a solution for a specific Unix command, say lsof, you might want to search CPAN first, before beginning to reinvent the wheel.

If you want Perl structures, maybe consider looking at the Perl functions. For example, ls is basically readdir combined with stat.