6.7.2. Using comments (prefixed by the '#' sign)

Most versions of sed permit comments to appear in sed scripts only on the first line of the script. Comments on line 2 or thereafter are not recognized and will generate an error like "unrecognized command" or "command [bad-line-here] has trailing garbage".

GNU sed, HHsed, sedmod, and HP-UX sed permit comments to appear on any line of the script, except after labels and branching commands (b,t), provided that a semicolon (;) occurs after the command itself. This syntax makes sed similar to awk and perl, which use a similar commenting structure in their scripts. Thus,

      # GNU style sed script
      $!N;                        # except for last line, get next line
      s/^\([0-9]\{5\}\).*\n\1.*//;    # if first 5 digits of each line
                                      # match, delete BOTH lines.
      t skip
      P;                              # print 1st line only if no match
      :skip
      D;                    # delete 1st line of pattern space and loop
      #---end of script---

is a valid script for GNU-based versions of sed, but is unrecognized for most other versions of sed.

Finally, if the first two characters in a disk file script are "#n", the output is suppressed, exactly as if -n were entered on the command line. This is true for the following versions of sed:

• ssed v3.57 and above
• gsed
• HHsed v1.5
• sed v1.6

This syntax is not recognized by these versions of sed:

• ssed v3.45 to v3.50 (other versions untested)
• sedmod v1.0