Edit an executable with bash without recompiling it?

Question

I'm trying to write a script for editing an executable (e.g. /bin/bash) in this way:

Search for a string - Replace old string with new string - Save changes to original file (obviously I'm trying on a copy of /bin/bash, for security reason)

My string is a single word. How can I do it?

Answer 1

You can easily modify a string in a binary file with sed but as noted in the comments it will most often only work when old and new string have the same length. With bash for example:

$ cp /bin/bash .
$ strings bash  | grep such
describe_pid: %ld: no such pid
    it creates, on systems that allow such control.
          such as cd which change the current directory.
%s: no such job
$ sed 's,no such job,no such boj,' -i bash
$ ./bash --noprofile --norc
bash-4.3$ kill %3333
bash: kill: %3333: no such boj

-i for sed is not in POSIX so if you want to achieve maximum portability:

$ cp /bin/bash .
$ sed 's,no such job,no such boj,' bash > bash.bak
$ mv bash.bak bash
$ chmod +x ./bash
$ ./bash --noprofile --norc
bash-4.3$ kill %3333
bash: kill: %3333: no such boj