Return digits from a string in bash shell

Question

i'd like to return only the digits from a string variable in bash shell. For example, for:

#!/bin/sh
file="./file_02.txt"
file_num_tag=?????????????????
echo $file_num_tag

...i'd like to return

>>> 02

I know this is super trivial, but I'm confusing myself searching around for answers and I'd like to know the best way to do it.

anubhava · Accepted Answer · 2015-03-19 18:34:46Z

6

You can use this BASH string replacement:

file="./file_02.txt"
echo "${file//[^[:digit:]]}"
02

[^[:digit:]] will match and remove all non-digits from your string file.

Or using tr (if not using BASH):

num=`echo "$file" | tr -cd '[[:digit:]]'`

answered Mar 19, 2015 at 18:34

anubhava

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4 Comments

And if you're on an ancient shell that doesn't support that kind of substitution: echo "${file}" | tr -cd '0-9'

Thanks, Yes that's right, let me add that also in answer.

@Jenny_Winters if this answer is exactly what you needed, then please accept it.

I will absolutely do that one the minimum time limit is up! Thanks for your suggestion!