How to extract a number from a string using grep and regex

Question

I make a cat of a file and apply on it a grep with a regular expression like this

cat /tmp/tmp_file | grep "toto.titi\[[0-9]\+\].tata=55"

the command display the following output

toto.titi[12].tata=55

is it possible to modify my grep command in order to extract the number 12 as displayed output of the command?

@AndrewLogvinov I can do it by adding the following pipes to my command | cut -f2 -d'[' | cut -f1 -d']' but I want to know how to it with the same grep — MOHAMED
– MOHAMED, Commented Dec 25, 2013 at 9:01
Yes it can be done in a single grep using -P (PCRE) switch. I provided an answer below. — anubhava
– anubhava, Commented Dec 25, 2013 at 9:08

anubhava · Accepted Answer · 2013-12-25 09:36:21Z

2

You can grab this in pure BASH using its regex capabilities:

s='toto.titi[12].tata=55'
[[ "$s" =~ ^toto.titi\[([0-9]+)\]\.tata=[0-9]+$ ]] && echo "${BASH_REMATCH[1]}"
12

You can also use sed:

sed 's/toto.titi\[\([0-9]*\)\].tata=55/\1/' <<< "$s"
12

OR using awk:

awk -F '[\\[\\]]' '{print $2}' <<<"$s"
12

edited Dec 25, 2013 at 9:36

answered Dec 25, 2013 at 9:05

anubhava

790k67 gold badges603 silver badges671 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

oyss · Accepted Answer · 2013-12-25 09:28:32Z

1

use lookahead

echo toto.titi[12].tata=55|grep -oP '(?<=\[)\d+'
12

without perl regex,use sed to replace "["

echo toto.titi[12].tata=55|grep -o "\[[0-9]\+"|sed 's/\[//g'
12

edited Dec 25, 2013 at 9:28

answered Dec 25, 2013 at 9:09

oyss

6921 gold badge8 silver badges20 bronze badges

2 Comments

MOHAMED Over a year ago

I m using a limited version of grep from busybox and it does not supported the -P option

oyss Over a year ago

@MOHAMED what about sed?match [12 and use sed to replace [.

Bohemian · Accepted Answer · 2013-12-25 09:04:50Z

0

Pipe it to sed and use a back reference:

cat /tmp/tmp_file | grep "toto.titi\[[0-9]\+\].tata=55" | sed 's/.*\[(\d*)\].*/\1/'

answered Dec 25, 2013 at 9:04

Bohemian♦

427k103 gold badges603 silver badges750 bronze badges

2 Comments

Jotne Over a year ago

You should now that grep can read files and cat is not needed.

Bohemian Over a year ago

@Jotne I do know that... I just took OP's partial solution and bolted on the extra part needed to do it

Collectives™ on Stack Overflow

How to extract a number from a string using grep and regex

3 Answers 3

Comments

2 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

2 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related