4.10. How do I perform a case-insensitive search?

Several versions of sed support case-insensitive matching: ssed and GNU sed v3.02+ (with I flag after s/// or /regex/); sedmod with the -i switch; and sed16 (which supports both types of switches).

With other versions of sed, case-insensitive searching is awkward, so people may use awk or perl instead, since these programs have options for case-insensitive searches. In gawk/mawk, use "BEGIN {IGNORECASE=1}" and in perl, "/regex/i". For other seds, here are three solutions:

Solution 1: convert everything to upper case and search normally

     # sed script, solution 1
     h;          # copy the original line to the hold space
                 # convert the pattern space to solid caps
     y/abcdefghijklmnopqrstuvwxyz/ABCDEFGHIJKLMNOPQRSTUVWXYZ/
                 # now we can search for the word "CARLOS"
     /CARLOS/ {
          # add or insert lines. Note: "s/.../.../" will not work
          # here because we are searching a modified pattern
          # space and are not printing the pattern space.
     }
     x;          # get back the original pattern space
                 # the original pattern space will be printed
     #---end of sed script---

Solution 2: search for both cases

Often, proper names will either start with all lower-case ("unix"), with an initial capital letter ("Unix") or occur in solid caps ("UNIX"). There may be no need to search for every possibility.

     /UNIX/b match
     /[Uu]nix/b match

Solution 3: search for all possible cases

     # If you must, search for any possible combination
     /[Ca][Aa][Rr][Ll][Oo][Ss]/ { ... }

Bear in mind that as the pattern length increases, this solution becomes an order of magnitude slower than the one of Solution 1, at least with some implementations of sed.