Regex for replacing space with comma-space, except at end of line

Question

I am trying to covert input file content of this:

NP_418770.2: 257-296 344-415 503-543 556-592 642-707
YP_026226.4: 741-779 811-890 896-979 1043-1077

to this:

NP_418770.2: 257-296, 344-415, 503-543, 556-592, 642-707
YP_026226.4: 741-779, 811-890, 896-979, 1043-1077

i.e., replace a space with comma and space (excluding newline)

For that, I have tried:

perl -pi.bak -e "s/[^\S\n]+/, /g" input.txt

but it gives:

NP_418770.2:, 257-296, 344-415, 503-543, 556-592, 642-707
YP_026226.4:, 741-779, 811-890, 896-979, 1043-1077

how can I stop the additional comma which appear after ":" (I want ":" and a single space) without writing another regex?

Thanks

Answer 1

Try using regex negative lookbehind. It is basically look if the character before the space is colon (:) then it don't match that space.

s/(?<!:)[^\S\n]+/, /g

Answer 2

You can play with the word-boundary to discard the space that follows the colon: s/\b\h+/, /g

It can be done with perl:

perl -pe's/\b\h+/, /g' file

but also with sed:

sed -E 's/\b[ \t]+/, /g' file

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Other approach that uses the field separator:

perl -F'\b\h+' -ape'BEGIN{$,=", "}' file

or do the same with awk:

awk -F'\b[ \t]+' -vOFS=', ' '1' file