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

Answer 1

You can say:

echo ${file%%[^0-9]*}

However, this runs into problems in certain cases:

$ file="123 file 456"
$ echo ${file%%[^0-9]*}
123

Using tr:

$ file="123 hello 456"
$ new=$(tr -dc '0-9' <<< $file)
$ echo $new
123456