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

$cat abs.sh
#!/bin/bash
echo "$(cd "$(dirname "$1")"; pwd -P)"

Some explanations:

1. This script get relative path as argument "$1"
2. Then we get dirname part of that path (you can pass either dir or file to this script): dirname "$1"
3. Then we cd "$(dirname "$1"); into this relative dir
4. pwd -P and get absolute path. The -P option will avoid symlinks
5. As final step we echo it

Then run your script:

abs.sh your_file.txt