I'm writing a Bash script. I need the current working directory to always be the directory that the script is located in.
The default behavior is that the current working directory in the script is that of the shell from which I run it, but I do not want this behavior.
Best Answer
TL;DR
The long winded explanation
How does this work and how does it deal with edge and corner cases?
bash
with some name which tellsbash
the script to run.bash
then callsdirname
with the bash argument which points to the script.bash
then callscd
with the output ofdirname
as its argument.bash
argumentdirname
argumentcd
argumentfoo
(found in$PATH
at/path/to/foo
)/path/to/foo
/path/to/foo
/path/to
bash foo
foo
foo
.
/foo
/foo
/foo
/
./foo
./foo
./foo
.
"/pa th/to/foo"
/pa th/to/foo
/pa th/to/foo
/pa th/to
"./pa th/to/foo"
./pa th/to/foo
./pa th/to/foo
./pa th/to
"../pa th/to/foo"
../pa th/to/foo
../pa th/to/foo
../pa th/to
"../../pa th/to/foo"
../../pa th/to/foo
../../pa th/to/foo
../../pa th/to
"pa th/to/foo"
pa th/to/foo
pa th/to/foo
pa th/to
--help/foo
--help/foo
*--help
On symlinks
The
cd
command will follow symlinks if they are involved. A symlink usually exists to be followed, so in most situations following the symlink is the correct thing to do. Why would it be a problem for the code in the script to follow a symlink when it was just fine to follow that same symlink a few microseconds ago when loading the script?On command arguments starting with hyphens
Elaborating on the two cases of arguments starting with hyphens in above table (marked with * and **, respectively):
* There is only one case where the argument to the
dirname
could begin with a-
, and that is the relative path case--help/foo
. If the script is in a subdirectory called--help
, the script execution will runbash --help/foo
, and bash does not know that option--help/foo
and will therefore abort with an error message. The script will never execute, so it does not matter what thecd "$(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 builtincd
will certainly accept--
), you can change the script snippet toPlease 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
.