You could be scanning through the file line for line and look for the name you want, (use the matching operator), split the line with 'split' modify your information delete the old line and add the new one. This might look something like this:

#!/usr/bin perl -w

use strict;

my $passfile = shift || 'passfile';
my $wantedname = shift || 'John Doe';
my $newpass = shift || '1234'; # example for changing a value
my $tempfile = $passfile.'temp'; # file where we copy all info for rem
+oving a line
my $searchstr = shift || 'abcd';
my $line; # line of the passfile


#first open the file
open(PFILE,"<$passfile") or die "unable to open $passfile, because $!\
+n";
#second open our tempfile
open(TEMP,">$tempfile") or die "unable to open $tempfile, because $!\n
+";

while ($line = <PFILE>){
  if ($line =~m/$wantedname/){
    print "Changing $line to ";
    #assume we now that we want to change the second element if we don
+'t a comparison will be easily implemented
    if($line =~s/$searchstr/$newpass/){ #put data back together
     print $line."\n"; # display line on screen
    }
   }
  print TEMP $line; # write line to temp file
}
#close original file
close PFILE or die "unable to close $passfile,because $!\n";
die "unable to delete $passfile, because $!\n" if (!unlink($passfile))
+;
# rename temp file to original file
rename $tempfile, $passfile or die "unable to rename file, because $!\
+n";
#done
print "\ndone.\n";
[download]

This does not work if the name is not unique or the value that you want to chang isn't.But anyway it is something :-)

Hope this helps,
C-Keen