There can be many reasons why you'd want to get the exact location of your currently running script. For example to calculate the relative path in a reliable way.
Luckily there is a command called realpath that will calculate and print the absolute path
of a given path.
Let's see how it works:
#!/bin/bash
echo $0
full_path=$(realpath $0)
echo $full_path
dir_path=$(dirname $full_path)
echo $dir_path
$0 is the name of the current script as it was executed. So if we run the script as ./examples/shell/absolute.sh
then that will be the content of $0.
realpath prints the abosulte path.
dirname prints the directory name, leaving the last part of the path which is in this case the name of the
file.
Let's see a couple of examples:
$ ./examples/shell/absolute.sh
./examples/shell/absolute.sh
/home/gabor/work/code-maven.com/examples/shell/absolute.sh
/home/gabor/work/code-maven.com/examples/shell
$ cd examples/shell/
$ ./absolute.sh # run right where it is
./absolute.sh
/home/gabor/work/code-maven.com/examples/shell/absolute.sh
/home/gabor/work/code-maven.com/examples/shell
$ cd ../../sites/en # go to a cousin of the scripts directory
$ ../../examples/shell/absolute.sh # run relatively from there
../examples/shell/absolute.sh
/home/gabor/work/code-maven.com/examples/shell/absolute.sh
/home/gabor/work/code-maven.com/examples/shell
$ ln -s ../../examples/shell/ # create a symbolic link to the directory
$ ./shell/absolute.sh # run using the symlink
./shell/absolute.sh
/home/gabor/work/code-maven.com/examples/shell/absolute.sh
/home/gabor/work/code-maven.com/examples/shell
$ ln -s ../../examples/shell/absolute.sh # create a symlink to the script
$ ./absolute.sh # run using the symlink
./absolute.sh
/home/gabor/work/code-maven.com/examples/shell/absolute.sh
/home/gabor/work/code-maven.com/examples/shell
$ /home/gabor/work/code-maven.com/examples/shell/absolute.sh # run with full path
/home/gabor/work/code-maven.com/examples/shell/absolute.sh
/home/gabor/work/code-maven.com/examples/shell/absolute.sh
/home/gabor/work/code-maven.com/examples/shell
$ export PATH=/home/gabor/work/code-maven.com/examples/shell:$PATH # make sure the directory of the script is in the path
$ cd # go home
$ absolute.sh # run without knowing where it is
/home/gabor/work/code-maven.com/examples/shell/absolute.sh
/home/gabor/work/code-maven.com/examples/shell/absolute.sh
/home/gabor/work/code-maven.com/examples/shell
As you can see in every case $ was exactly as we invoked the script. Except of the last case where we invoked
it by name only and relied on the content of the PATH environment variable and the shell to find the script.
In that case $0 already contained the full path.
However the 2nd and 3rd line of output were exactly the same in every case.
So we can rely on the realpath to consistently return the real full path of the script.
Even if we execute it via a symbolic link.
