Thanks. I gave Linux::usermod->del(username); a try and see that it leaves the groups in /etc/group and /etc/shadow untouched instead of removing / modifying them as needed. I took a look at the source for Linux::usermod and it's over my skill level to dig in and form a patch, at least in a timely manner.

I'll look into several options now but it may take some time.

It looks like this is the distilled version of what I will try. The validation of the two variables takes place earlier in another function.

$ENV{'PATH'}=q(/sbin:/bin:/usr/sbin:/usr/bin);

my ($um,$gm);

qx/usermod --login $newname --home $newname $oldname/;
$um = $?;
if ($um==0) {
    qx/groupmod --new-name $newname $oldname/;
    $gm = $?;
}
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Ideas or corrections?

No output is produced, so I don't try to capture any. And the home directory gets reassigned and renamed elsewhere, too, since I have a little non-standard home directory arrangement for those groups.

Since you're setting a restricted PATH, are you running this under taint mode? If so, are $newname and $oldname user input? If yes, I would strongly recommend against putting them in a shell command like this (even though I assume you had to untaint them first). I'd suggest at the very least using system in the list form with more than one argument, e.g.:

system('usermod','--login',$newname,'--home',$newname,$oldname)
    ==0 or die "usermod failed, \$?=$?";
system('groupmod','--new-name',$newname,$oldname)
    ==0 or die "groupmod failed, \$?=$?";
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I wrote more on the topic of avoiding the shell here.

It runs under taint mode. As mentioned earlier in the thread, the script does sanitization and validation of the strings earlier on long before they get sent to the shell scripts. I would avoid using the system programs directly if possible, but Linux::usermod is missing the functions needed to proerly rename an account belonging to several groups.

Could you please explain the advantages or differences between system() in list form and qx/ / in practice? I'm only interested in tracking if the action failed or succeeded and wish to suppress anything sent to stdin or stdout.

If you don't need the output, use system instead of qx. It returns the exit code directly, so no need to use $?.
map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]