Cooking With Technology

Converting a Relative Path to an Absolute Path in Bash

This really shouldn’t have taken me as long as it did to figure this out, but it was a big enough of an annoyance that I decided to share it.

How to convert a relative path to an absolute path in linux/unix/bash script:

#!/bin/bash

# Assume parameter passed in is a relative path to a directory.

# For brevity, we won't do argument type or length checking.

echo "Absolute path: `cd $1; pwd`"

For those unaware, you don’t have to ‘cd -’ because the backticks perform command substitution and don’t modify the working directory of the script.

EDIT: Anonymous poster ‘foo’ left a comment mentioning that this only works if the path destination already exists, which is indeed the case. This isn’t at all elegant, but it is the ‘two minute hack’ version I could immediately come up with. The result only works if you have permission to write where the path should go, meaning *yes,* there will be a version three of this script when I have more time:

#!/bin/bash
# Alright, this time we'll do parameter checking.

if [ $# -eq 0 ]; then
	echo "Usage: $0 "
	exit 1
fi

if [ -d $1 ]; then
	# Paramater is an existing directory. Print it using the method in the script above.
	echo "Absolute path: `cd $1; pwd`"

elif [[ -e $1 && ! -d $1 ]]; then
	# File already exists and isn't a directory. Be more safe with the conversion.
	mkdir $1$$ 2> /dev/null
	if[ $? -ne 0 ]; then
		echo "We cannot conver this path without write permissions to the path's destination."
		exit 1
	fi
	# I don't want to escape the quotes. This is already ugly, anyway.
	dirName=`cd $1$$; pwd | awk -F"$$" {'print $1'}`
	echo "Absolute path: $dirName"
	rm -r $1$$
else
	# File doesn't exist, begin unelegant conversion
	mkdir $1 2> /dev/null
	if [ $? -ne 0 ]; then
		echo "We cannot convert this path without write permissions to the path's destination."
		exit 1
	fi
	echo "Absolute path: `cd $1; pwd`"
	rm -r $1
fi

Secondary notes: I really wrote this on the spot in a couple minutes, directly into this blog post. It is untested, and very ugly. I promise to post something better soon!