TL;DR
#!/bin/bash
cd "$(dirname "$0")"
The long winded explanation
How does this work and how does it deal with edge and corner cases?
- You type a command launching the script in your interactive shell.
- That interactive shell calls
bash with some name which tells bash the script to run.
- That
bash then calls dirname with the bash argument which points to the script.
- Finally, that
bash then calls cd with the output of dirname as its argument.
| script invocation command |
bash argument |
dirname argument |
cd argument |
foo (found in $PATH at /path/to/foo) |
/path/to/foo |
/path/to/foo |
/path/to |
bash foo |
foo |
foo |
. |
/foo |
/foo |
/foo |
/ |
./foo |
./foo |
./foo |
. |
"/pa th/to/foo" |
/pa th/to/foo |
/pa th/to/foo |
/pa th/to |
"./pa th/to/foo" |
./pa th/to/foo |
./pa th/to/foo |
./pa th/to |
"../pa th/to/foo" |
../pa th/to/foo |
../pa th/to/foo |
../pa th/to |
"../../pa th/to/foo" |
../../pa th/to/foo |
../../pa th/to/foo |
../../pa th/to |
"pa th/to/foo" |
pa th/to/foo |
pa th/to/foo |
pa th/to |
--help/foo |
--help/foo * |
N/A |
N/A |
--help |
N/A ** |
N/A |
N/A |
On symlinks
The cd command will follow symlinks if they are involved. A symlink usually exists to be followed, so in most situations following the symlink is the correct thing to do. Why would it be a problem for the code in the script to follow a symlink when it was just fine to follow that same symlink a few microseconds ago when loading the script?
On command arguments starting with hyphens
Elaborating on the two cases of arguments starting with hyphens in above table (marked with * and **, respectively):
* There is only one case where the argument to the dirname could begin with a -, and that is the relative path case --help/foo. If the script is in a subdirectory called --help, the script execution will run bash --help/foo, and bash does not know that option --help/foo and will therefore abort with an error message. The script will never execute, so it does not matter what the cd "$(dirname "$0")" would have executed.
** Note that calling the script --help makes the shell not find the command when you are typing --help in the same directory. Alternatively, with $PATH containing the current directory, the script will be run as /path/to/--help or ./--help, always with something in front of the - character.
Unless bash introduces command line arguments with a parameter separated by a =, it is unlikely to impossible to pass a - argument to bash which contains a / later, and which is accepted by bash.
If you can rely on dirname accepting -- argument (bash builtin cd will certainly accept --), you can change the script snippet to
cd -- "$(dirname -- "$0")"
Please do comment if you can figure out a way to construct an argument beginning with - which can be sneaked past bash.
Nota bene
The above snippet also works with non-bash /bin/sh.
Best Answer
When you start your script, a new process is created that only inherits your environment. When it ends, it ends. Your current environment stays as it is.
Instead, you can start your script like this:
The
.will evaluate the script in the current environment, so it might be altered