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Inverting match with grep, unless another term exists

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.


<span style="color:#323232;">[A,B]
</span><span style="color:#323232;">[A,C]
</span><span style="color:#323232;">[B,C]
</span><span style="color:#323232;">[A]
</span><span style="color:#323232;">[B]
</span>

I can reverse grep for B:


<span style="color:#323232;">> grep --invert-match "B"
</span><span style="color:#323232;">[A,C]
</span><span style="color:#323232;">[A]
</span>

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

Andy , (edited )
@Andy@programming.dev avatar 

<span style="color:#323232;">grep -E </span><span style="color:#183691;">'(^[^B]*$|A)'
</span>

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.

TheLugal OP ,
@TheLugal@lemmy.world avatar

Haha, on Lemmy.World it looks like a top level. Thank you, either way :)

bizdelnick ,

You don’t need parentheses here.

Andy ,
@Andy@programming.dev avatar

How dare you?

Thanks!

borf ,

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.

TheLugal OP ,
@TheLugal@lemmy.world avatar

Thank you! This was exactly was I was looking for. :)

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