CODEWITHSUNDEEP
linuxfileshellsedreplace
Mark
Mark

Reputation: 1996

modifying a text file with regex

I have a source file containing a specific string, and would like to replace the first (in this case, only) instance of that string with the contents of another file. Something like: 

> cat source.txt
Hello
KEYWORD
Hi
> cat replacement.txt
Replacement
> <sed command>
> cat source.txt
Hello
Replacement
Hi

Is there a way to do this with sed? Or any other editor?

Upvotes: 0

Views: 781

Answers (3)

Kent
Kent

Reputation: 195239

I think awk may do this job easier:

if you want to keep the ending linebreak in replace.txt:

awk -v RS="\0" -v ORS="" 'NR==FNR{r=$0;next}{sub(/KEYWORD/,r)}1' replace.txt source.txt

if you want to strip the ending \n from replace.txt:

awk -v RS="\0" -v ORS="" 'NR==FNR{r=$0;sub(/\n$/,"",r);next}{sub(/KEYWORD/,r)}1'  replace.txt source.txt

the above line works no matter your replace.txt has single or multiple lines.

e.g.:

kent$  head file1 file2                                                         
==> file1 <==
Hello
KEYWORD
Hi
KEYWORD

==> file2 <==
rep_line1
rep_line2

kent$  awk -v RS="\0" -v ORS="" 'NR==FNR{r=$0;next}{sub(/KEYWORD\n/,r)}1' file2 file1
Hello
rep_line1
rep_line2
Hi
KEYWORD

you can see, only the first KEYWORD in file1 was replaced. however Awk cannot write change back to the input file. what we could do is:

awk '...' replace.txt src.txt > /tmp/t.txt && mv /tmp/t.txt /path/to/src.txt

the awk one-liner was tested with gawk. No guarantee that it will work for all awk implementations. you should test it, if you got a non-gnu awk.

thank Ed Morton's suggestions.

Upvotes: 1

tink
tink

Reputation: 15238

$ cat source.txt
Hello
KEYWORD

Hi



KEYWORD

KEYWORD

$ cat replacement.txt 
Replacement
multiline?
$ sed -ir  "0,/KEYWORD/s//$(cat replacement.txt | sed 's/$/^M/'|tr -d '\n' ) )/" source.txt 
$ cat source.txt
Hello
Replacement
multiline?
Hi



KEYWORD

KEYWORD

$

Upvotes: 0

Ding
Ding

Reputation: 3085

A quick and easy way:

sed s/KEYWORD/`cat replacement.txt`/ source.txt > output.txt

Upvotes: 0

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