Including break line in sed replacement

Question

I've got the following sed replacement, which replaces an entire line with different text, if a certain string is found in the line.

sed "s/.*FOUNDSTRING.*/replacement \"text\" for line"/ test.txt

This works fine - but, for example I want to add a new line after 'for'. My initial thought was to try this:

sed "s/.*FOUNDSTRING.*/replacement \"text\" for \n line"/ test.txt

But this ends out replacing with the following:

replacement "text" for n line

Desired outcome:

replacement "text" for 
line

Answer 1

It can be painful to work with newlines in sed. There are also some differences in the behaviour depending on which version you're using. For simplicity and portability, I'd recommend using awk:

awk '{print /FOUNDSTRING/ ? "replacement \"text\" for\nline" : $0}' file

This prints the replacement string, newline included, if the pattern matches, otherwise prints the line $0.

Testing it out:

$ cat file
blah
blah FOUNDSTRING blah
blah
$ awk '{print /FOUNDSTRING/ ? "replacement \"text\" for\nline" : $0}' file
blah
replacement "text" for
line
blah

Of course there is more than one way to skin the cat, as shown in the comments:

awk '/FOUNDSTRING/ { $0 = "replacement \"text\" for \n line" } 1' file

This replaces the line $0 with the new string when the pattern matches and uses the common shorthand 1 to print each line.