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Say I have a text file like this:

# custom content section
a
b

### BEGIN GENERATED CONTENT
c
d
### END GENERATED CONTENT

I'd like to replace the portion between the GENERATED CONTENT tags with the contents of another file.

What's the simplest way to do this?

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3 Answers 3

Warning: This is definitely not the simplest way to do it. (EDIT: bash works; POSIX grep is fine too)

If the main text is in file "main" and the generated content is in file "gen", you could do the following:

#!/bin/bash
BEGIN_GEN=$(cat main | grep -n '### BEGIN GENERATED CONTENT' | sed 's/\(.*\):.*/\1/g')
END_GEN=$(cat main | grep -n '### END GENERATED CONTENT' | sed 's/\(.*\):.*/\1/g')
cat <(head -n $(expr $BEGIN_GEN - 1) main) gen <(tail -n +$(expr $END_GEN + 1) main) >temp
mv temp main
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Does this work? I think your last line will open main for writing, clearing it, before it is read by cat. –  chepner Jun 22 '12 at 14:05
    
@chepner Crap, you're right. The rest works, though. I'll fix it. –  Dr Kitty Jun 22 '12 at 18:39
up vote 2 down vote accepted
newContent=`cat new_file`
perl -0777 -i -pe "s/(### BEGIN GENERATED CONTENT\\n).*(\\n### END GENERATED CONTENT)/\$1$newContent\$2/s" existing_file
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Nice job. Much simpler than mine. :) –  Dr Kitty Jun 22 '12 at 6:12
lead='^### BEGIN GENERATED CONTENT$'
tail='^### END GENERATED CONTENT$'
sed -e "/$lead/,/$tail/{ /$lead/{p; r insert_file
        }; /$tail/p; d }"  existing_file
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Excellent. sed can do so much more than just s/.../...! –  DevSolar Jun 22 '12 at 8:28
    
Hmmm does not work for me, should I put the sed command on one line? –  lzap Jul 11 at 11:15
    
The r insert_file command must be the last thing on its line. Note that neither whitespace nor comments are allowed after it. The code was tested using GNU sed with the --posix option enabled, and it worked as expected, so it should work with any posix compliant sed. –  Peter.O Jul 12 at 1:58

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