How to replace 2 consecutive lines after Match with Sed

Question

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

Answer 1

You can repeat the commands:

gsed '/^#ABC/{n;s/Size=bar/Size=foo/;n;s/Size=bar/Size=foo/}' file

See the online demo .

The n command " prints the pattern space, then, regardless, replace the pattern space with the next line of input. If there is no more input then sed exits without processing any more commands. "

So, the first time it is used, you replace on the first line after line starting with #ABC , then you replace on the second line below that one.

Answer 2

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

Answer 3

Using sed , the loop will break when Size=bar is no longer found therefore replacing the first 2 lines after the match.

$ sed '/^#ABC/{:l;n;s/Size=bar/Size=foo/;tl}' input_file
#ABC
oneSize=foo
twoSize=foo
threeSize=foo

Answer 4

Using sed -z

sed -z 's/#ABC\noneSize=bar\ntwoSize=bar/#ABC\noneSize=foo\ntwoSize=foo/' file.txt
#ABC
oneSize=foo
twoSize=foo
threeSize=foo

Or

sed -E -z 's/#ABC\n(.*)bar\n(.*)bar/#ABC\n\1foo\n\2foo/' file.txt