Question

Running a string search/replace search and concered that some strings may be contained in those files, does sed ignore them because of the binary type structure, or could they destroy the function?

Answer 1

This is really a “try it and see what happens” sort of question, so…

• Start with a copy of the wtmp file.

  $ cp /var/log/wtmp wtmp.work
  

• Look at it using who:

  $ who wtmp.work
  lars     pts/2        2012-10-23 10:58 (:0)
  lars     pts/2        2012-10-23 11:01 (:0)
  lars     pts/2        2012-10-23 11:11 (:0)
  lars     pts/2        2012-10-23 11:43 (:0)
  lars     pts/2        2012-10-23 12:41 (:0)
  lars     pts/2        2012-10-23 12:41 (:0)
  

• Let’s try placing “lars” with “superman”:

  $ sed -i s/lars/superman/ wtmp.work
  

• And see what happened:

  $ who wtmp.work
  superman pts/7        1969-12-31 19:00
  

Oops.

Hopefully that answers your question!