Obviously, I'm a little late to this party, but I stumbled across this while checking to see whether I'd have to (re)invent a wheel to answer a question on the Perl Beginners mailing list. This is the solution I ultimately came up with:

#!/usr/local/bin/perl -l
use strict;
use warnings;

my $user = $ARGV[0];
my @gr_list;
my @pw_info;

while (@pw_info = getpwent) {
  if ($pw_info[0] eq $user) {
    my @gr_info;
    while (@gr_info = getgrent) {
      push(@gr_list, $gr_info[2]) if ($gr_info[3] =~ /\b$user\b/);
    }
    push(@gr_list, $pw_info[3]);
  }
}

print foreach @gr_list;

[download]

It's not stunningly terse or clean-looking, at least in my estimation, but it works and doesn't involve calling out to external system utilities.

print substr("Just another Perl hacker", 0, -2);
 - apotheon
CopyWrite Chad Perrin

In reply to Re: Fetching groups a user is in by apotheon
in thread Fetching groups a user is in by belg4mit

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.