Follow Techotopia on Twitter

On-line Guides
All Guides
eBook Store
iOS / Android
Linux for Beginners
Office Productivity
Linux Installation
Linux Security
Linux Utilities
Linux Virtualization
Linux Kernel
System/Network Admin
Scripting Languages
Development Tools
Web Development
GUI Toolkits/Desktop
Mail Systems
Eclipse Documentation

How To Guides
General System Admin
Linux Security
Linux Filesystems
Web Servers
Graphics & Desktop
PC Hardware
Problem Solutions
Privacy Policy




The sed FAQ
Prev Home Next

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
      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
The sed FAQ
Prev Home Next

   Reprinted courtesy of Eric Pement. Also available at Design by Interspire