Script Execution Permissions | Engineering Notes

Allow a script to be executed as a program by setting the correct execution permission.

In Linux, a file must have execute (x) permission before it can run as a script.

Linux uses file permissions to control who can:

Read (r) → view the file

Write (w) → modify the file

Execute (x) → run the file as a program

Permissions are defined for three categories:

User (u) → file owner

Group (g) → users in the same group

Others (o) → all other users

Without execute permission, the script cannot be run directly (you will see an error like Permission denied).

bash

nano script.sh

Add the following content:

bash

#!/bin/bash
echo "Hello DevOps"

Save and exit.

bash

ls -l script.sh

Example output:

bash

-rw-r--r-- 1 user user 30 Mar 4 script.sh

This shows there is no execute permission yet.

bash

chmod +x script.sh

Check again:

bash

ls -l script.sh

Example output:

bash

-rwxr-xr-x 1 user user 30 Mar 4 script.sh

Now the script is executable.

bash

chmod +x script.sh

Adds execute permission for all users. It is equivalent to:

bash

chmod a+x script.sh

Where a means u + g + o.

bash

./script.sh

Output:

bash

Hello DevOps

chmod +x makes the script executable.

./script.sh runs the script from the current directory.

Avoid using chmod 777 unless absolutely necessary.

Follow the least privilege principle.