Anonymous Monk,
There are a few things in your post that make providing a solution difficult.

  • If you are worried about speed, it usually comes at the cost of space (in this case memory).
  • If you are worried about memory, it usually comes at a cost of speed.
  • You haven't indicated how long your script is going to be running. Sometimes it is worth it to spend time at the beginning of the script if subsequent lookups will outweigh that time.
  • You haven't indicated how often your script is going to be checking for users. It may be a moot point (premature optimization) to even be worried.
  • You haven't indicated if you only want to know if the user exists, or if you also want some other information such as their home directory (which you mentioned as a validation means).

    You also indicate that you would like to add users that are not on your system. It is for this reason that I suggest using a hash lookup (which is very fast) in this untested code. 

    #!/usr/bin/perl -w
use strict;
my %User;

{
    local @ARGV;    
    @ARGV = qw(/etc/passwd /usr/defined/file);    
    while (<>) {
        chomp;
        my @field = split /:/;
        unless (exists $User{$field[0]}) {
            $User{$field[0]} = \@field;
        }
        else {
            print "WARNING:  Duplicate found for $field[0]\n";
        }
    }
}
my $testuser = "blah";
if (exists $User{$testuser}) {
    print "$testuser exists on system\n";
    print "Field 4 for $testuser is $User{$testuser}->[3]\n";
}

    [download]
    Of course /user/defined/file should be set up like /etc/passwd if you care about the extra fields. Additionally, if you don't want to use /etc/passwd - I have shown the framework - you can have an "ok" %User and a "blacklist" %BadUser.

    Cheers - L~R

    In reply to Re: User Existance? by Limbic~Region
    in thread User Existance? by Anonymous Monk

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