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Bash Guide For Beginners

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2.1.3. Executing the script

The script should have execute permissions for the correct owners in order to be runnable. When setting permissions, check that you really obtained the permissions that you want. When this is done, the script can run like any other command:


   

willy:~/scripts>
chmod u+x script1.sh

willy:~/scripts> ls -l script1.sh
-rwxrw-r-- 1 willy willy 456 Dec 24 17:11 script1.sh

willy:~> script1.sh
The script starts now.
Hi, willy!

I will now fetch you a list of connected users:

3:38pm up 18 days, 5:37, 4 users, load average: 0.12, 0.22, 0.15
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
root tty2 - Sat 2pm 4:25m 0.24s 0.05s -bash
willy :0 - Sat 2pm ? 0.00s ? -
willy pts/3 - Sat 2pm 3:33m 36.39s 36.39s BitchX willy ir
willy pts/2 - Sat 2pm 3:33m 0.13s 0.06s /usr/bin/screen

I'm setting two variables now.
This is a string: black
And this is a number: 9

I'm giving you back your prompt now.

willy:~/scripts> echo $COLOUR

willy:~/scripts> echo $VALUE

willy:~/scripts>

This is the most common way to execute a script. It is preferred to execute the script like this in a subshell. The variables, functions and aliases created in this subshell are only known to the particular bash session of that subshell. When that shell exits and the parent regains control, everything is cleaned up and all changes to the state of the shell made by the script, are forgotten.

If you did not put the scripts directory in your PATH , and . (the current directory) is not in the PATH either, you can activate the script like this:

./script_name.sh

A script can also explicitly be executed by a given shell, but generally we only do this if we want to obtain special behavior, such as checking if the script works with another shell or printing traces for debugging:

rbash script_name.sh

sh script_name.sh

bash -x script_name.sh

The specified shell will start as a subshell of your current shell and execute the script. This is done when you want the script to start up with specific options or under specific conditions which are not specified in the script.

If you don't want to start a new shell but execute the script in the current shell, you source it:

source script_name.sh


       source = .
        

The Bash source built-in is a synonym for the Bourne shell . (dot) command.

The script does not need execute permission in this case. Commands are executed in the current shell context, so any changes made to your environment will be visible when the script finishes execution:


   

willy:~/scripts> source script1.sh
--output ommitted--

willy:~/scripts> echo $VALUE
9

willy:~/scripts>


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