[SOLVED] How to replace 2 consecutive lines after Match with Sed

Issue

Is there a way to replace the following two lines after a match is found using sed?

I have a file

#ABC
oneSize=bar
twoSize=bar
threeSize=foo

But I would like to replace the two immediate lines once the pattern #ABC is matched so that it becomes

#ABC
oneSize=foo
twoSize=foo
threeSize=foo

I'm able to do gsed '/^#ABC/{n;s/Size=bar/Size=foo/}' file

But it only changes the line twoSize not oneSize

Is there a way to get it to change both oneSize and twoSize

Solution

gnu and some other sed versions allow you to grab a range using relative number so you can simply use:

sed -E '/^#ABC$/,+2 s/(Size=)bar/\1foo/' file
#ABC
oneSize=foo
twoSize=foo
threeSize=foo

Command details:

• /^#ABC$/,+2 Match range from pattern #ABC to next 2 lines
• s/(Size=)bar/\1foo/: Match Size=bar and replace with Size=foo, using a capture group to avoid repeat of same String in search and substitution

---

You may also consider awk to avoid repeating pattern and replacements N times if you have to replace N lines after matching pattern:

awk 'n-- {sub(/Size=bar/, "Size=foo")} /^#ABC$/ {n=2} 1' file

#ABC
oneSize=foo
twoSize=foo
threeSize=foo

Answered By - anubhava

Answer Checked By - Clifford M. (WPSolving Volunteer)