Bash relative path to absolute path [duplicate] - 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 other files.
I would like the script to go to the folder containing the input file, to execute further commands.
In Linux, how do I get the folder (and just the folder) from an input file?

Answer 1

To get the full path use:
readlink -f relative/path/to/file
To get the directory of a file:
dirname relative/path/to/file
You can also combine the two:
dirname $(readlink -f relative/path/to/file)
If readlink -f is not available on your system you can use this*:
function myreadlink() {
(
cd "$(dirname $1)" # or cd "${1%/*}"
echo "$PWD/$(basename $1)" # or echo "$PWD/${1##*/}"
)
}
Note that if you only need to move to a directory of a file specified as a relative path, you don't need to know the absolute path, a relative path is perfectly legal, so just use:
cd $(dirname relative/path/to/file)
if you wish to go back (while the script is running) to the original path, use pushd instead of cd, and popd when you are done.
* While myreadlink above is good enough in the context of this question, it has some limitation relative to the readlink tool suggested above. For example it doesn't correctly follow a link to a file with different basename.

Answer 2

Take a look at realpath which is available on GNU/Linux, FreeBSD and NetBSD, but not OpenBSD 6.8. I use something like:
CONTAININGDIR=$(realpath ${FILEPATH%/*})
to do what it sounds like you're trying to do.

Answer 3

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
}

Answer 4

$cat abs.sh
#!/bin/bash
echo "$(cd "$(dirname "$1")"; pwd -P)"
Some explanations:
This script get relative path as argument "$1"
Then we get dirname part of that path (you can pass either dir or file to this script): dirname "$1"
Then we cd "$(dirname "$1"); into this relative dir
pwd -P and get absolute path. The -P option will avoid symlinks
As final step we echo it
Then run your script:
abs.sh your_file.txt

Answer 5

Try our new Bash library product realpath-lib over at GitHub that we have given to the community for free and unencumbered use. It's clean, simple and well documented so it's great to learn from. You can do:
get_realpath <absolute|relative|symlink|local file path>
This function is the core of the library:
if [[ -f "$1" ]]
then
# file *must* exist
if cd "$(echo "${1%/*}")" &>/dev/null
then
# file *may* not be local
# exception is ./file.ext
# try 'cd .; cd -;' *works!*
local tmppwd="$PWD"
cd - &>/dev/null
else
# file *must* be local
local tmppwd="$PWD"
fi
else
# file *cannot* exist
return 1 # failure
fi
# reassemble realpath
echo "$tmppwd"/"${1##*/}"
return 0 # success
}
It's Bash 4+, does not require any dependencies and also provides get_dirname, get_filename, get_stemname and validate_path.

Answer 6

Problem with the above answer comes with files input with "./" like "./my-file.txt"
Workaround (of many):
myfile="./somefile.txt"
FOLDER="$(dirname $(readlink -f "${ARG}"))"
echo ${FOLDER}

Answer 7

I have been using readlink -f works on linux
so
FULL_PATH=$(readlink -f filename)
DIR=$(dirname $FULL_PATH)
PWD=$(pwd)
cd $DIR
#<do more work>
cd $PWD