If we know a specific substring we want to extract from a variable by where it starts, and optionally how long it is, we can use the ${var:start} or ${var:start:length} form:
bash$ title='== Password =='
bash$ printf '%s\n' "${title:3}"
Password ==
bash$ printf '%s\n' "${title:3:8}"
Password
By specifying a negative start value, you can start the counting from the end of the string, starting at -1:
bash$ alpha='abcdefghijk'
bash$ printf '%s\n' "${alpha: -3:2}"
ij
Note that we had to add a space prefix before the minus sign, to prevent the shell from interpreting this as the unrelated :- form.
