How to grep one string after pattern?

Question

I would like to get the string from the file after user defined keyword. Example if keyword is "yellow_y", expected output to be acc.

Tried grep -oP '(?<=yellow_y).*' but not work.

File:

yellow      abc \
yellow_x     abc \
yellow_y      acc \
blue     abb \
pink abb \
pink_xx acd \

It seems another case for awk, awk '$1 == "yellow_y"{print $2}' file — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Dec 2, 2021 at 12:07

RavinderSingh13 · Accepted Answer · 2021-12-02 12:09:36Z

2

With your shown samples, please try following grep command. Written and tested in GNU grep.

grep -oP '^yellow_y\s+\K\S+'  Input_file

Online demo for above regex

Explanation: Simple explanation would be, using -oP options of GNU grep which is for printing matched words and enabling PCRE regex respectively. In main program using regex to match condition. Checking if line starts from yellow_y followed by 1 or more spaces then using \K capability of GNU grep to forget this match and matching 1 or more non-spaces characters then which will provide required values in output.

answered Dec 2, 2021 at 12:09

RavinderSingh13

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3 Comments

Ярослав Рахматуллин Over a year ago

Do you know where the \K is mentioned in the manual / info pages? maybe this? perldoc.perl.org/perlre#Extended-Patterns (would have never guessed \K means that)

RavinderSingh13 Over a year ago

@ЯрославРахматуллин, Honestly I learnt it from Gurus in SO itself, after your comment I checked man pages and help but couldn't find it(at least in my grep version), but searching online I found this learnbyexample.gitbooks.io/command-line-text-processing/content/… site which has it. But doesn't look like it mentions too many details about it(though they have given few examples for it).

Blurman Over a year ago

thanks. I modify it based on my needs and it is working

Wiktor Stribiżew · Accepted Answer · 2021-12-02 13:15:34Z

0

To get acc, you can also use awk here instead of grep:

awk '$1 == "yellow_y"{print $2}' file

This means: if the first word (first non-whitespace chunk) is yellow_y, return the second non-whitespace chunk of characters (the second word).

See an online demo:

#!/bin/bash
s='yellow      abc \
yellow_x     abc \
yellow_y      acc \
blue     abb \
pink abb \
pink_xx acd \'
awk '$1 == "yellow_y"{print $2}' <<< "$s"

Output is acc.

answered Dec 2, 2021 at 13:15

Wiktor Stribiżew

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