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Editorial Team
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Asked: 2026-05-14T14:53:17+00:00

I want to extract a substring matching a pattern and save it to a

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I want to extract a substring matching a pattern and save it to a file. An example string:

Apr 12 19:24:17 PC_NMG kernel: sd 11:0:0:0: [sdf] Attached SCSI removable disk

I want to extract the part between the brackets, in this case [sdf].

I tried to do something like grep -e '[$subtext]' to save the text in the brackets to a variable. Of course it doesn’t work, but I am looking for a way similar to this. It would be very elegant to include a variable in a regex like this. What can I do best?

Thanks!

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1 Answer

  1. Editorial Team

    There’s probably a better way using bash only, but:

    echo 'Apr 12 19:24:17 PC_NMG kernel: sd 11:0:0:0: [sdf] Attached SCSI removable disk' \
| sed -s 's/.*\[\(.*\)\].*/\1/'

    As Jurgen points out, this matches non-matching lines. If you don’t want to output nonmatching lines, use ‘-n’ so it doesn’t output the pattern, and ‘/p’ to outputs the pattern when it matches.

    | sed -n 's/.*\[\(.*\)\].*/\1/p'
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