Print line after the match in grep

Question

I'm trying to get the current track running from 'cmus-remote -Q' Its always underneath of this line

 tag genre Various
 <some track>

Now, I need to keep it simple because I want to add it to my i3 bar. I used

cmus-remote -Q | grep -A 1 "tag genre"

but that grep's the 'tag' line AND the line underneath.

I want ONLY the line underneath.

What about just excluding the RE with another pipe? `cmus-remote -Q | grep -A 1 "tag genre" | grep -v "tag genre"` ? It fails if the RE is on two lines in a row, of course. — ghoti, Nov 18 '16 at 11:51
If your `grep` supports `-P` option then it's so simple, `grep -oPz 'tag genre.*\n\K.*' file` — Avinash Raj, Nov 18 '16 at 12:01

score 2 · Answer 1 · answered Nov 18 '16 at 12:06

2

With sed:

sed -n '/tag genre/{n;p}'

Output:

$ cmus-remote -Q | sed -n '/tag genre/{n;p}'
<some track>

answered Nov 18 '16 at 12:06

sat

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anubhava · Answer 2 · 2016-11-18T12:02:20.787

1

You can use awk instead of grep:

awk 'p{print; p=0} /tag genre/{p=1}' file

<some track>

/tag genre/{p=1} - sets a flag p=1 when it encounters tag genre in a line.
p{print; p=0} when p is non-zero then it prints a line and resets p to 0.

edited Nov 18 '16 at 12:02

answered Nov 18 '16 at 11:52

anubhava

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Thanks , that works as well , but I think the grep -v , Is just easier : – KeVy0 Nov 18 '16 at 11:55
1

Hmm but that invokes 2 commands instead of just one with awk – anubhava Nov 18 '16 at 11:56
1

Ok , fair enough :). Thanks – KeVy0 Nov 18 '16 at 12:00
1

This solution also assumes that you only want to do this search once per file. I don't think that was a criterion on the question. – ghoti Nov 18 '16 at 12:01
We can replace `exit` by `p=0` to get multiple matches. – anubhava Nov 18 '16 at 12:02

score 1 · Accepted Answer · answered Nov 18 '16 at 11:58

If you want to use grep as the tool for this, you can achieve it by adding another segment to your pipeline:

cmus-remote -Q | grep -A 1 "tag genre" | grep -v "tag genre"

This will fail in cases where the string you're searching for is on two lines in a row. You'll have to define what behaviour you want in that case if we're going to program something sensible for it.

Another possibility would be to use a tool like awk, which allows for greater compexity in the line selection:

cmus-remote -Q | awk '/tag genre/ { getline; print }'

This searches for the string, then gets the next line, then prints it.

Another possibility would be to do this in bash alone:

while read line; do
  [[ $line =~ tag\ genre ]] && read line && echo "$line"
done < <(cmus-remote -Q)

This implements the same functionality as the awk script, only using no external tools at all. It's likely slower than the awk script.

score 0 · Answer 4 · answered Nov 18 '16 at 11:54

I'd suggest using awk:

awk 'seen && seen--; /tag genre/ { seen = 1 }'

when seen is true, print the line.
when seen is true, decrement the value, so it will no longer true after the desired number of lines are printed
when the pattern matches, set seen to the number of lines to be printed

Print line after the match in grep

4 Answers4