How replace data in a file from a bash script?

Question

I need to modify the data of a binary file stored in disk, from bash script. How to do this?

(For example, I need to open a file with 100 byte size and replace data 0x00 at 50th byte position with 0xff)

I tried google, but unable to find the answer. Any help is appreciated.

Thank you.

Answer 1

Perl to the rescue:

#!/usr/bin/perl
use warnings;
use strict;

use Fcntl qw{ SEEK_SET SEEK_CUR };

my $pos = 50;

open my $BIN, '+<:raw', shift or die $!;
seek $BIN, $pos - 1, SEEK_SET or die "Can't seek into file.\n";

my $size = read $BIN, my $data, 1;
die "Can't read 50th byte from file.\n" unless $size;

if ("\0" eq $data) {
    seek $BIN, - 1, SEEK_CUR;
    print {$BIN} "\xff";
    close $BIN;
} else {
    warn "Nothing to replace, 50th byte isn't a zero.\n";
}

• +< opens the file in the read/write mode.
• :raw removes any IO layers (e.g. CRLF translation)
• seek rewinds the position in a filehandle.