How to remove all non-numeric characters from a string in Bash?

Question

Example:

file="123 hello" 

How can I edit the string file such that it only contains the numbers and the text part is removed?

So,

echo $file 

should print 123 only.

Answer 1

This is one way with sed:

$ echo $file | sed 's/[^0-9]*//g'  123 $ echo "123 he23llo" | sed 's/[^0-9]*//g' 12323 

Or with pure bash:

$ echo "${file//[!0-9]/}"  123 $ file="123 hello 12345 aaa" $ echo "${file//[!0-9]/}"  12312345 

To save the result into the variable itself, do

$ file=$(echo $file | sed 's/[^0-9]*//g') $ echo $file 123  $ file=${file//[!0-9]/} $ echo $file 123