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I am maintaing a linux driver and I want to replace all %p in driver with %pK. For doing this i used following command.

grep "%p[^K]" -Rl . | xargs sed -i 's/%p[^K]/%pK/g'

It fails in below case.

%p-%p --> %pK%pK (hyphen is removed)

Please suggest proper regular expressionfor sed command to work.

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  • I think you are looking for a way to assert that %p is not followed by K and then replace... one way is to use perl with lookarounds... ex: echo '%p-%p' | perl -pe 's/%p(?!K)/%pK/g'
    – Sundeep
    Oct 28, 2016 at 7:07
  • @Sundeep I am trying to do same, but I want to make changes in all files in all position where %p is present ( not %pK). So is there any way to do same with sed. I tried following but did not work. grep "%p[^K]" -Rl . | xargs sed -i 's/%p(?!K)/%pK/g' Oct 28, 2016 at 8:28
  • try echo '%p-%p' | sed -E 's/%p([^K]|$)/%pK\1/g'... and I would suggest grep -RlZ '%p[^K]' | xargs -0 sed -i -E 's/%p([^K]|$)/%pK\1/g' to prevent issues with filenames containing special characters... also I hope you are trying this out on test folders instead of directly applying changes on actual files.. you can do that once you have a working solution
    – Sundeep
    Oct 28, 2016 at 8:33
  • sed doesn't have lookaround regex, that is why I suggested perl..
    – Sundeep
    Oct 28, 2016 at 8:40

2 Answers 2

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The sed replacement in the question would remove any characters after a %p, not just dashes, since the [^K] is part of the matched string. You can work around that by capturing the character after %p with (escaped) parenthesis, and putting it back with \1. In sed:

$ echo '%p %p %pK' | sed 's/%p\([^K]\)/%pK\1/g'
%pK %pK %pK

Though you might want to use [^a-zA-Z] or similar just in case you were to use other modifiers for %p.

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Following command did magic for me

for fname in $(grep "%p[^K]" -Rl .); do perl -pi -e 's/%p(?!K)/%pK/g' $fname; done

Thanks Sundeep, Your comment helped a lot. :)

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  • That is an answer, though it would be much better with an explanation, so it would be independent of the comments.
    – ilkkachu
    Oct 28, 2016 at 9:17

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