Mysterious GNU sed option “-E”

A few days ago I needed to conduct a mass search and replace operation on a large text file, and figured that sed would be a good fit. I must admit that sed is not on the list of tools I use daily, so I just looked up a solution to a similar problem on the Net. It worked, but the command line contained an option I’ve never seen before – capital “E“:

sed -E . . .

Without -E, the command failed, so I decided to find out what that option means. However, it seemed to be undocumented: neither sed --help nor man sed or info sed mentioned it.

Fast forward a few minutes, and I have the answer: it is simply equivalent to “-r“!

           .  .  .
        /* Undocumented, for compatibility with BSD sed.  */
        case 'E':
        case 'r':
          if (extended_regexp_flags)
            usage(4);
          extended_regexp_flags = REG_EXTENDED;
          break;
           .  .  .

Sigh. Every now and then I wish Unix was never forked or cloned.

I also wondered if there is reciprocity on the BSD side, but I only have access to an old box running FreeBSD 4.11 – the version of sed included with it does not recognize the “-r” option…

Tags: sed

This entry was posted on Friday, March 18th, 2011 at 11:38 pm and is filed under Small Hacks. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.