Perl or Python script to remove user from group

Question

I am putting together a Samba-based server as a Primary Domain Controller, and ran into a cute little problem that should have been solved many times over. But a number of searches did not yield a result. I need to be able to remove an existing user from an existing group with a command line script. It appears that the usermod easily allows me to add a user to a supplementary group with this command:

usermod -a -G supgroup1,supgroup2 username

Without the "-a" option, if the user is currently a member of a group which is not listed, the user will be removed from the group. Does anyone have a perl (or Python) script that allows the specification of a user and group for removal? Am I missing an obvious existing command, or well-known solution forthis? Thanks in advance!

Thanks to J.J. for the pointer to the Unix::Group module, which is part of Unix-ConfigFile. It looks like the command deluser would do what I want, but was not in any of my existing repositories. I went ahead and wrote the perl script using the Unix:Group Module. Here is the script for your sysadmining pleasure.

#!/usr/bin/perl
#
# Usage:   removegroup.pl login group
# Purpose: Removes a user from a group while retaining current primary and
#          supplementary groups.
# Notes:   There is a Debian specific utility that can do this called deluser,
#          but I did not want any cross-distribution dependencies
#
# Date:   25 September 2008

# Validate Arguments (correct number, format etc.)
if ( ($#ARGV < 1) || (2 < $#ARGV) ) {
  print "\nUsage: removegroup.pl login group\n\n";
  print "EXIT VALUES\n";
  print "     The removeuser.pl script exits with the following values:\n\n";
  print "     0 success\n\n";
  print "     1 Invalid number of arguments\n\n";
  print "     2 Login or Group name supplied greater than 16 characters\n\n";
  print "     3 Login and/or Group name contains invalid characters\n\n";
  exit 1;
}

# Check for well formed group and login names
if ((16 < length($ARGV[0])) ||(16 < length($ARGV[1])))
{
  print "Usage: removegroup.pl login group\n";
  print "ERROR: Login and Group names must be less than 16 Characters\n";
  exit 2;
}

if ( ( $ARGV[0] !~ m{^[a-z_]+[a-z0-9_-]*$}) || ( $ARGV[0] !~ m{^[a-z_]+[a-z0-9_-]*$} ) )
{
  print "Usage: removegroup.pl login group\n";
  print "ERROR: Login and/or Group name contains invalid characters\n";
  exit 3;
}

# Set some variables for readability
$login=$ARGV[0];
$group=$ARGV[1];

# Requires the GroupFile interface from perl-Unix-Configfile
use Unix::GroupFile;

$grp = new Unix::GroupFile "/etc/group";
$grp->remove_user("$group", "$login");
$grp->commit();
undef $grp;
exit 0;

Is that a general comment, or is there something obvious and silly that I wrote into the script? — Loren Charnley, May 13 '09 at 12:10

score 2 · Answer 1 · answered Sep 24 '08 at 19:15

2

I found This for you. It should do what you need. As far as I can tell Perl does not have any built in functions for removing users from a group. It has several for seeing the group id of a user or process.

answered Sep 24 '08 at 19:15

J.J.

4,856
1
24
29

score 2 · Accepted Answer · answered Jan 20 '09 at 18:42

Web Link: http://www.ibm.com/developerworks/linux/library/l-roadmap4/

To add members to the group, use the gpasswd command with the -a switch and the user id you wish to add:

gpasswd -a userid mygroup

Remove users from a group with the same command, but a -d switch rather than -a:

gpasswd -d userid mygroup

"man gpasswd" for more info...

I looked for ages to find this. Sometimes it takes too much effort not to reinvent the wheel...

Dave, Amazing - who'd thunk that the command would look like a password utility ... Thanks! Loren — Loren Charnley, Feb 13 '09 at 20:52

score 1 · Answer 3 · answered Sep 24 '08 at 18:42

1

It looks like deluser --group [groupname] should do it.

If not, the groups command lists the groups that a user belongs to. It should be fairly straightforward to come up with some Perl to capture that list into an array (or map it into a hash), delete the unwanted group(s), and feed that back to usermod.

answered Sep 24 '08 at 18:42

Dave Sherohman

45,363
14
64
102

On the Centos 5 installation I am working with, there does not appear to be a "deluser" installed on the system. I am currently looking for it in the repositories. I have started working on a perl script, but it will probably take me an hour or two to get the perl side of my brain spooled back up. – Loren Charnley Sep 24 '08 at 18:53
Apparently deluser is Debian specific. – Loren Charnley Sep 25 '08 at 16:27

score 1 · Answer 4 · answered Sep 24 '08 at 19:54

Here's a very simple little Perl script that should give you the list of groups you need:

my $user = 'user';
my $groupNoMore = 'somegroup';
my $groups = join ',', grep { $_ ne $groupNoMore } split /\s/, `groups $user`;

Getting and sanitizing the required arguments is left as an execrcise for the reader.

Perl or Python script to remove user from group

4 Answers4