Bash relative vs. absolute paths

bash-paths.sh

#!/usr/bin/env bash

# There are many ways to get a path to a file or script.
# This script showcases several of them and their pitfalls.

# Credit for most of these techniques comes from:
# http://stackoverflow.com/questions/4774054/

abs_path='/usr/bin/bash'
rel_path='.'

###########################################################
# Using dirname
###########################################################

# dirname works great when given an absolute path.
dirname "$abs_path"

# But only gives a relative path otherwise.
dirname "$rel_path"

###########################################################
# Using readlink -f
###########################################################

# readlink -f works great and even works for symlinks.
readlink -f "$abs_path"
readlink -f "$rel_path"

# Unfortunately, it only works on Linux, not on macOS.

###########################################################
# Using a combination of cd and pwd
###########################################################

# The most reliable way to get an absolute path is a
# combination of cd and pwd. Just make sure to do it
# in a subshell, lest you change your current directory.

(cd "$(dirname "$abs_path")" && pwd)
(cd "$(dirname "$rel_path")" && pwd)

###########################################################
# Resolving symlinks
###########################################################

# The cd && pwd method can be used to resolve symlinks
# by using the -P option to pwd.

(cd "$(dirname "$abs_path")" && pwd -P)
(cd "$(dirname "$rel_path")" && pwd -P)

###########################################################
# Getting the location of a script
###########################################################

# But what if you want to know the location of the script
# you are currently running? You have two options.

# $0 returns the name of the script you are running
# but returns -bash if you source the script.

echo "$0"
(cd "$(dirname -- "$0")" && pwd -P)

# ${BASH_SOURCE[0]} always returns the name of the script,
# even if you source the file.

echo "${BASH_SOURCE[0]}"
(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd -P)

# Note that I wrap all variables and the output of these
# variables in double quotes. This is intentional, as
# any spaces in the filenames or directories could cause
# unintended consequences.

thanks a million!