Extract substring in Bash

Question

Given a filename in the form someletters_12345_moreleters.ext, I want to extract the 5 digits and put them into a variable.

So to emphasize the point, I have a filename with x number of characters then a five digit sequence surrounded by a single underscore on either side then another set of x number of characters. I want to take the 5 digit number and put that into a variable.

I am very interested in the number of different ways that this can be accomplished.

Answer 1

just try to use cut -c startIndx-stopIndx

Answer 2

My answer will have more control on what you want out of your string. Here is the code on how you can extract 12345 out of your string

str="someletters_12345_moreleters.ext"
str=${str#*_}
str=${str%_more*}
echo $str

This will be more efficient if you want to extract something that has any chars like abc or any special characters like _ or -. For example: If your string is like this and you want everything that is after someletters_ and before _moreleters.ext :

str="someletters_123-45-24a&13b-1_moreleters.ext"

With my code you can mention what exactly you want. Explanation:

#* It will remove the preceding string including the matching key. Here the key we mentioned is _ % It will remove the following string including the matching key. Here the key we mentioned is '_more*'

Do some experiments yourself and you would find this interesting.