bash – Difference Between ‘source x’, ‘. x’ and ‘./x’ in Bash

bashscripts

I have one bash source run.sh as follows,

#!/bin/bash
if [ $# -ne 1 ]; then
    exit
fi
...

when I execute it in two ways, there are different behaviors. The first way is,

source run.sh

It will close the terminal after execution. The second way is,

./run.sh

this will simply finish running the script, and stay on the terminal. I am asking if there is a command for exiting a bash scripts for both source run.sh and ./run.sh execution. I have tried return too, which does not work well under ./run.sh execution.

More generally, I am interested in why this is happening, and what's difference between using "source" and "." for script execution?

Best Answer

Before answering, I think some clarifications are needed. Let's analyze the following three lines:

source run.sh
. run.sh
./run.sh

The first two lines are exactly identical: . is in fact an alias for source. What source does is executing the shell script in the current context, hence a call to exit will quit the shell.

The third line (which is the one that confuses you) has however nothing to do with the other lines. ./run.sh is just a path, and is the same as (for example) /home/user/run.sh or /usr/bin/something. Always remember that commands in the shell are separated by a space. So, in this case, the command is not ., but is ./run.sh: this means that a sub-shell will be executed and that the exit will have effect just to the sub-shell.

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