What does this mean? $ . test.sh

Question

I saw the command like ". test.sh" in some shell source code, but I don't know what it does. So, I have tried this. And, that .sh file is executed.

However, I don't understand how "." works. Can you explain?

Answer 1

The . command (which has a synonym, source, in bash, but not in most other Bourne shell derivatives) reads the named file as part of the current shell.

Consider:

$ cat test.sh
export ENVVAR="Welcome"
echo $ENVVAR
$ echo $ENVVAR

$ test.sh
Welcome
$ echo $ENVVAR

$ . test.sh
Welcome
$ echo $ENVVAR
Welcome
$

^{NB: Cheat 1: I assume test.sh is executable. Cheat 2: I assume test.sh is in a directory on $PATH.}

It means that environment variables set in test.sh affect the current shell. By contrast, executing a command without the . does not affect the environment of the current shell. The . mechanism is used when .profile and related files are read, for example.

Note that . looks for simple names (like test.sh with no slash in it) on PATH, but the file only has to be readable; it does not have to be executable.

Answer 2

It's a shorthand for this, nothing more:

source test.sh

http://ss64.com/bash/period.html