I would like to modify a line in the /etc/passwd (gcos) file after I've found it...WITHOUT the use of modules (so it can be used on a fresh perl install

Now we wouldn't be trying to make a hacking tool now would we?

FYI - A Fresh PERL install comes with a lot of handy modules included.

Here's a hint, start with:

open(FH, "< $filename") or die ("Can't read file: $!\n");
@the_file = <FH>;
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Then you could play with the contents of @the_file & write the whole thing back out again. (Assuming you close and open(FH, "> $filename") again.

Now AFAIK the IO module installs with a basic PERL installation. So a better way to do this might be:

use IO::File;

$fh = IO::File->new($filename, "r+")
     or die "Couldn't open $filename for read & write: $!\n";
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I hope I have been of some useful guidance...

Wait! This isn't a Parachute, this is a Backpack!