ok you are right it was easy,but may I ask another question? if you have

 my $sentence = 'The quick brown fox jumped over the lazy dog';
    my $substring = 'quick.*?fox';
    $sentence =~ s{$substring}{big bad wolf};
[download]

you get an output of 'The big bad wolf jumped over the lazy dog',but how can I tell him to ignore even "The" from the sentence but not by using :

 my $sentence = 'The quick brown fox jumped over the lazy dog';
    my $substring = 'The.*?fox';
    $sentence =~ s{$substring}{big bad wolf};
[download]

but by telling him to ignore 4 characters before "quick"

Change your regex to include those four characters:

    my $substring = '....quick.*?fox';
[download]

last 2 questions, if you have something like

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

    open my $input, '<', $ARGV[0];
        while (my $sentence = <$input>) {
            my $substring = '...pck.*?.c';
            $sentence =~ s{$substring}{}; 
    open my $out, '>', 'hex.txt';    
    print $out unpack 'H*', $sentence;
      }
[download]

in your file you have something like file:123/pck/asd/cara.casddma , it will read the value from "1" to "ara.casddma" even tho I used ".c" not "c" , 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" and second I would like to replace the text in the file with blank not with a space.