Using grep to match only a match group in a regular expression?

Question

I need to set my keyboard layout with setxkbmap before launching Wine games, as I use Dvorak for typing and this breaks every game's controls. What I'd like to do is simply write a script that grabs the current keyboard layout before starting the game, stores it in a variable, then restores it after the game is done:

ORIGINAL_LAYOUT=`setxkbmap -query | grep -P 'layout\:\s{5}(\w+)'`
setxkbmap us
wine ...
setxkbmap $ORIGINAL_LAYOUT

The problem that I'm having is that grep matches the entire line and not just my capture group. Is there a way for me to simply dump the matched capture group?

For example, the output of setxkbmap -query is:

rules:      evdev
model:      pc105
layout:     dvorak

I'm interested in grabbing the layout.

See this answer: http://unix.stackexchange.com/questions/24722/returning-a-portion-of-a-line-matching-a-pattern/24725#24725 — camh, Jan 02 '12 at 22:24
possible duplicate of Can grep output only specified groupings that match? — Gilles 'SO- stop being evil', Jan 02 '12 at 23:40

phemmer · Answer 1 · 2012-01-03T19:51:59.993

6

You can use -o and change the grep a little bit

   -o, --only-matching
          Print  only the matched (non-empty) parts of a matching line, with each such
          part on a separate output line.

.

ORIGINAL_LAYOUT=`setxkbmap -query | grep -oP '(?<=layout\:\s{5})\w+'`

We changed the regex to use a look-behind so its not part of the match

edited Jan 03 '12 at 19:51

answered Jan 02 '12 at 20:06

phemmer

71,831

This would have returned the full line, not the part between parentheses. – Lekensteyn Jan 02 '12 at 21:40
1

@Lekensteyn This is why you modify the regex to use look-behind... – phemmer Jan 03 '12 at 12:46
Include that in your answer then. Nifty trick btw, it never occured to me to use lookbehind in grep. – Lekensteyn Jan 03 '12 at 13:43
@Lekensteyn advice taken – phemmer Jan 03 '12 at 19:53
2

Note: -P is not supported since OSX Lion and on BSD grep – kenorb Sep 24 '13 at 09:57

harish.venkat · Accepted Answer · 2012-01-02T19:17:07.410

5

Try using this awk command:

setxkbmap -query | grep layout | awk '{print $2}'

or use cut command

setxkbmap -query | grep layout | cut -d : -f2

edited Jan 02 '12 at 19:17

answered Jan 02 '12 at 18:50

harish.venkat

7,573

3

The grep is unnecessary, see jasonwryan's comment to the question. – Mat Jan 02 '12 at 18:58

Using grep to match only a match group in a regular expression?

2 Answers2