Sed: adding a substring in the middle of a variable

Question

I'm trying to change the directory of all C headers like #include "library.h" to #include "prefix/library.h" in a file using the sed command, but I can't figure out how to add a prefix to the middle of a string. So far I've tried this command:

sed -i "s"\/'#include[[:space:]]*[<"][^>"]*[>"]'\/"$prefix"\/ $filename

but it replaces the whole string instead of creating #include "prefix/library.h". Is there any way to change it while keeping the original #include, <, " and spacing?

Welcome to SO, could you please post more clear samples of your Input and expected output in your post inside CODE TAGS and let us know then. — RavinderSingh13
– RavinderSingh13, Commented Oct 19, 2019 at 12:40
It's not clear what output you desire. You seem to be looking for sed backreferences; briefly, & lets you recall the entire matched string, and \1, \2 etc backslash-parenthesized subexpressions from the match. You also seem to need a thorough refresher on the shell's quoting facilities. — tripleee
– tripleee, Commented Oct 19, 2019 at 12:41
I'm sorry for being unclear, I'm trying to for example change #include <header.h> to #include <prefix/header.h> — Šaman Bobo
– Šaman Bobo, Commented Oct 19, 2019 at 12:44

Chris Maes · Accepted Answer · 2019-10-19 12:48:29Z

1

you could use this:

sed "s%#include[[:space:]]*[<\"]%&$prefix/%" $filename

explanation:

You can use any separator with sed, I use % as a separator, to avoid trouble with / inside your filename
& means: the whole matched regex. To this way the pattern you just matched is printed again.
this command searches for #include " and adds the $prefix just after that match.

answered Oct 19, 2019 at 12:48

Chris Maes

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2 Comments

Šaman Bobo Over a year ago

Thank you, & to match the regex was what I was looking for :)

Chris Maes Over a year ago

You're welcome. Welcome to SO. If an answer solves your question, please accept it (you'll get 2 reputation points). If any answer was helpful, you can upvote it (once you have enough reputation).

RavinderSingh13 · Accepted Answer · 2019-10-20 02:12:03Z

1

Could you please try following.

sed 's/\([^"]*\)\(\"\)\(.*\)/\1\2prefix\/\3/'  Input_file

Output will be as follows.

#include "prefix/library.h"

In case you have a shell variable then try following.

prefix="prefix"
sed "s/\([^\"]*\)\(\"\)\(.*\)/\1\2$prefix\/\3/" Input_file

Where your Input_file is as follows:

cat Input_file
#include "library.h"

edited Oct 20, 2019 at 2:12

answered Oct 19, 2019 at 12:46

RavinderSingh13

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