Hello N0obieMonk, and welcome to the Monastery!

(1) In a regex, a dot matches any character other than a newline (unless your regex has an /s modifier, in which case . matches a newline too). If you want to match the literal substring “.c”, you need to escape the dot: \.c

(2) How is a “blank” different from a space?

But my main purpose in replying is to point out a logic error in the code snippet shown. open my $out, '>', 'hex.txt'; will re-open and truncate the output file on each iteration of the while loop, and you’ll end up with file “hex.txt” containing only a single entry from the last loop iteration. You need to open the output file for writing before the while loop, so that the filehandle $out is initialized only once.

Update: Added “the literal substring” to point (1).

Hope that helps,

you mean something like this?

use warnings 'all';
use strict;
use autodie;

    open my $input, '<', $ARGV[0];
    open my $out,   '>', 'hex.txt';

        while (my $sentence = <$input>) {
    
            my $substring = '...pck.*?\.c';
            $sentence =~ s{$substring}{}; 
        print $out unpack 'H*', $sentence;             
 
    }
[download]

and thank you for the nice explanations :D

from your last explanation I know now that it will read 1 char before c but I must ask how can you tell it to read until ".c" not "c"

See perlrebackslash

I would like to replace the text in the file with blank not with a space.

See chomp