How do I get the absolute directory of a file in bash?

Question

I have written a bash script that takes an input file as an argument and reads it.
This file contains some paths (relative to its location) to additional files used.

Answer 1

This will work for both file and folder:

absPath(){
    if [[ -d "$1" ]]; then
        cd "$1"
        echo "$(pwd -P)"
    else 
        cd "$(dirname "$1")"
        echo "$(pwd -P)/$(basename "$1")"
    fi
}