In Bash, I want to get the Nth word of a string after a matching pattern with awk or grep

Question

In Bash, I want to get the Nth word of a string after a matching pattern with awk.

Example text:

hadf asdfi daf PATTERN asdf dsjk PRINT_THIS asdf adas
asdf sdf PATTERN asdf dasdf PRINT_THIS ads asdf PATTERN ads da PRINT_THIS
ads PATTERN ads da PRINT_THIS

Excepted output:

PRINT_THIS
PRINT_THIS
PRINT_THIS
PRINT_THIS

So if a pattern is found, the second word after the match should be output.

How can i do this?

What's a "pattern"? [how-do-i-find-the-text-that-matches-a-pattern](https://stackoverflow.com/questions/65621325/how-do-i-find-the-text-that-matches-a-pattern) — Ed Morton, Sep 22 '22 at 12:17
_How can i do this?_ Probably with `awk`, but it depends on what a pattern is: a glob? a regex? a literal string? — Fravadona, Sep 22 '22 at 12:18

dawg · Accepted Answer · 2022-09-22T13:10:31.073

3

With GNU grep:

grep -oP '.*?\bPATTERN(?:\h+\H+){2}\h+\K\S+' file

Perl:

perl -lnE 'while (/.*?\bPATTERN(?:\h+\H+){2}\h+(\S+)/g) { say $1; }' file

Demo and explanation of regex

Or with awk:

awk '/PATTERN[[:blank:]]/{for(i=1;i<=NF-3;i++) if ($i ~ /^PATTERN$/) print $(i+3)}' file

All print:

PRINT_THIS
PRINT_THIS
PRINT_THIS
PRINT_THIS

edited Sep 22 '22 at 13:10

answered Sep 22 '22 at 12:47

dawg

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Andrej Podzimek · Answer 2 · 2022-09-22T13:26:07.437

So, should it be in Bash or with awk or grep? In Bash you can do the following:

while read -ra tokens; do
  for idx in "${!tokens[@]}"; do
    [[ "${tokens[idx]}" = 'PATTERN' ]] && printf '%s\n' "${tokens[idx + 3]}"
  done
done

In case the tokens between PATTERN and PRINT_THIS cannot contain another PATTERN, you could make it a bit more wannabe-efficient (and uglier), like this:

while read -ra tokens; do
  for ((idx = 0; idx < ${#tokens[@]}; ++idx)); do
    [[ "${tokens[idx]}" = 'PATTERN' ]] && printf '%s\n' "${tokens[idx += 3]}"
  done
done

Notice the += instead of +, as in “making loops hard to read 101”.

Last but not least, declare -i idx step would make it (even) a tiny bit more efficient.

In Bash, I want to get the Nth word of a string after a matching pattern with awk or grep

2 Answers2