4.24. How do I address all the lines between RE1 and RE2, excluding the lines themselves?

Normally, to address the lines between two regular expressions, RE1 and RE2, one would do this: '/RE1/,/RE2/{commands;}'. Excluding those lines takes an extra step. To put 2 arrows before each line between RE1 and RE2, except for those lines:

     sed '1,/RE1/!{ /RE2/,/RE1/!s/^/>>/; }' input.fil

The preceding script, though short, may be difficult to follow. It also requires that /RE1/ cannot occur on the first line of the input file. The following script, though it's not a one-liner, is easier to read and it permits /RE1/ to appear on the first line:

     # sed script to replace all lines between /RE1/ and /RE2/,
     # without matching /RE1/ or /RE2/
     /RE1/,/RE2/{
       /RE1/b
       /RE2/b
       s/^/>>/
     }
     #---end of script---

   Contents of input.fil:         Output of sed script:
      aaa                           aaa
      bbb                           bbb
      RE1                           RE1
      aaa                           >>aaa
      bbb                           >>bbb
      ccc                           >>ccc
      RE2                           RE2
      end                           end