How do I use grep to parse a portion of bash command output into a variable?

Question

$ file myImage.png

Produces this result:

myImage.png: PNG image data, 42 x 64, 8-bit grayscale, non-interlaced

I want to parse the width and the height into variables, something like this:

MY_WIDTH  = file myImage.png | grep ???x
MY_HEIGHT = file myImage.png | grep x???

Try awk. You can use it to parse out fields (i.e. columns) of output. — Trenin
– Trenin, Commented Jan 2, 2014 at 15:42

chepner · Accepted Answer · 2014-01-02 15:46:55Z

5

You can use subgroup capturing with a regular expression match:

regex='([0-9]+) x ([0-9]+)'
[[ $(file myImage.png) =~ $regex ]] && {
    MY_WIDTH=${BASH_REMATCH[1]}
    MY_HEIGHT=${BASH_REMATCH[2]}
}

answered Jan 2, 2014 at 15:46

chepner

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1 Comment

John Kugelman Over a year ago

Great answer. Bonus +1 for putting the regex in a variable. Bash changed the way it does regexes between 3.1 and 3.2, so storing them in a variable gives maximum compatibility.

Anders Lindahl · Accepted Answer · 2014-01-02 16:06:36Z

4

If you are indeed interested in the resolution of an image, there are better utilities than file in the imagemagick package. Specifically the identify tool:

MY_WIDTH=$(identify -format "%w" myImage.png)
MY_HEIGHT=$(identify -format "%h" myImage.png)

edited Jan 2, 2014 at 16:06

answered Jan 2, 2014 at 15:58

Anders Lindahl

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Comments

Community · Accepted Answer · 2017-05-23 11:49:39Z

0

I beleive you will need a regular expression that detects the ' x ' pattern with the numbers on either side.

This thread may help you start as it says:

xrandr|grep -Po '\d+(?=\s*x.*\*.*)'

instead you could do

RES = file myImage.png ||grep -Po '\d+(?=\s*x.*\*.*)'

then modify accordingly to seperate the two into your variables

edited May 23, 2017 at 11:49

CommunityBot

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answered Jan 2, 2014 at 15:48

LOGMD

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1 Comment

chepner Over a year ago

There are several syntax errors, and you ignore the difficult part of parsing two substrings out of the result of the grep.

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