How to obtain the absolute path of a file via Shell (BASH/ZSH/SH)?

Question: is there a simple sh/bash/zsh/fish/... command to print the absolute path of whichever file I feed it?

Usage case: I'm in directory /a/b and I'd like to print the full path to file c on the command-line so that I can easily paste it into another program: /a/b/c. Simple, yet a little program to do this could probably save me 5 or so seconds when it comes to handling long paths, which in the end adds up. So it surprises me that I can't find a standard utility to do this — is there really none?

Here's a sample implementation, abspath.py:

#!/usr/bin/python
# Author: Diggory Hardy <[email protected]>
# Licence: public domain
# Purpose: print the absolute path of all input paths

import sys
import os.path
if len(sys.argv)>1:
    for i in range(1,len(sys.argv)):
        print os.path.abspath( sys.argv[i] )
    sys.exit(0)
else:
    print >> sys.stderr, "Usage: ",sys.argv[0]," PATH."
    sys.exit(1)

Use realpath

$ realpath example.txt
/home/username/example.txt

Try readlink which will resolve symbolic links:

readlink -e /foo/bar/baz