Prepending a header file

# sed script to put header.txt above first line
#  run with sed -i -f <this_script> <filename(s)>
1{h; r header.txt
  D; }
2{x; G; }

changes only pieces inside a section

Say for a section like this...

[centosplus]
name=CentOS-$releasever - Plus
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
#baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/ gpgcheck=1
enabled=0
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4

This will change enabled=0 to enabled=1 only for this section, overwrite the old file and save a backup: sed --in-place=_old '/\[centosplus\]/,/^\[/s/enabled=0/enabled=1/' the_file

Grouping-like stuff in substitution

Say you want to change home to home_sweet_home...use the () to select the group, then \1 to substitute it back in

echo "dummy:x:505:509::/home/dummy:/bin/bash" | sed 's/\/home\/\(.*\):/\/home_sweet_home\/\1:/g'

Search and replace in a file

sed 's/zork/Pork/gi' zorkstuff.txt | less

Like, throw out the .wav extension on a bunch of files ls *.wav |sed 's!\.wav$!!'

Replace every occurrence (the g specifier) of 'Zork' with 'Pork' ignoring case (i specifier)

Print first 5 lines

sed '5q' file

Print until you find 'blah', then stop

sed '/blah/q' file

Print line 52 of file

sed '52q;d' file

strip out lines that have a match in them

See also

• This is a great starting point for sed help.
• these one-liners

-- MattWalsh - 21 Oct 2003