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I have a file with many strings. For simplicity, assume it is newline-delimited, and that each string is made up of only contain alphanumeric ASCII characters and underscore.

Now, I want to search a file / multiple files for occurrences of any of these strings. If there are not very many of them, I suppose I could just concatenate them with | and use a single grep. But - what if there are thousands, or tens of thousands, of them?

  • grep -f file_with_patterns files*? – fedorqui May 3 '18 at 7:56
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You can use your file with many strings, one per line, as an argument to grep’s -f option, which tells it to look for strings listed in the named file:

grep -f patterns.txt *

(or whatever glob is appropriate). grep will find any line in the given files which match any of the patterns in patterns.txt.

You probably should specify -F too if all the strings are fixed strings to match.

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