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After looking for solutions online I can grep for two hyphens without issue with grep -r "\-\-" or grep -r \\ --. But the files grep searches sometimes have lines full of hyphens, for example in comments, e.g. /*--------- comment ----- */. I want to grep to return cases where only two hyphens are next to each other. E.g. -- and not ---. Ideally I could use -w but I'm not having luck with this.

And a second piece of the puzzle is, if somehow I can grep for only two consecutive hyphens --, I want to find the pattern as though it was a perfect match like -w would do. So something like i--; would not feature as a result. But i -- would. Maybe there's a simple solution but I can't seem to figure it out.

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At least if you have GNU grep, you could use PCRE lookarounds to match a pair of hyphens that are neither preceded nor followed by a hyphen:

grep -P '(?<!-)--(?!-)' file

or

grep -Pw '(?<!-)--(?!-)' file

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