I have a list containing a set of tags, and would like to exclude one tag, unless another tag exists in the line.

Say I have the following list, and want to exclude B, unless A is present.

[A,B]
[A,C]
[B,C]
[A]
[B]

I can reverse grep for B:

> grep --invert-match "B"
[A,C]
[A]

How can I find the previous list, but also the item containing [A,B]?

  • Andy@programming.dev
    7·
    9 months ago
    grep -E '(^[^B]*$|A)'

    EDIT: Whoops, I meant to make this a top-level comment.

    EDIT 2: On one client it looked like a nested comment and on this other client it looks top level and now I’m a confused old man.

  • borf@lemmynsfw.comEnglish
    7·
    9 months ago

    I like to use awk instead of grep wherever possible, especially for weird logic like this.

    awk '!/B/ || /A.*B/' is one way to skin that cat. If you don’t care what order A and B are in on the lines containing both, then awk '!/B/ || (/A/ && /B/)' will work.