How to Get a Substring Using Positive and Negative Indexes in Bash

Question

What I want is pretty simple. Given a string 'this is my test string,' I want to return the substring from the 2nd position to the 2nd to last position. Something like: substring 'this is my test string' 1,-1. I know I can get stuff from the beginning of the string using cut, but I'm not sure how I can calculate easily from the end of the string. Help?

Answer 1

Turns out I can do this with awk pretty easily as follows:

echo 'this is my test string' | awk '{ print substr( $0, 2, length($0)-2 ) }'

Answer 2

Be cleaner in awk, python, perl, etc. but here's one way to do it:

#!/usr/bin/bash

msg="this is my test string"
start=2
len=$((${#msg} - ${start} - 2))

echo $len

echo ${msg:2:$len}

results in is is my test stri

Answer 3

You can do this with just pure bash

$ string="i.am.a.stupid.fool.are.you?"
$ echo ${string:  2:$((${#string}-4))}
am.a.stupid.fool.are.yo