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Using sed to match regexp patterns in a file with a fixed string (not the other way around) (lemmy.eco.br)

submitted 2 days ago* (last edited 2 days ago) by [email protected] to c/shell

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Hi there!

Usually, sed can be used in different ways, but most of the time we use it to match lines in a file against a fixed regexp. Some examples:

This replaces ocurrences of regexp for "foo":

sed 's/regexp/foo/g' < myfile

This prints all lines that have "foo", but will change the first "o" in the line for an "a":

sed -n '/foo/s/o/a/p' < myfile

and so on...

But I tried to do a different thing, with no success: can I pass to sed a file with a bunch of regular expressions and test them against a fixed string? I tried to play with pattern space, hold space, with no success. It just seems impossible to use them (which would be the closest to "variables") in search commands.

I know sed is Turing complete, but using it that way would maybe require to implement a regexp engine from scratch?

Thanks!

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[–] [email protected] 1 points 2 days ago

What result do you need? Do you just nedd to know if one of the regexps matched the string, or do you need to know which one, or is it something else?