Proper way to run a bash script file extension

Introduction

Running a bash script is a common task that many server administrators perform. However, it is important to run them in the proper way to avoid any potential security risks. In this blog post, we will discuss the proper way to run a bash script file extension, including using the correct shell and naming conventions.

Using the Correct Shell

When running a bash script, it is important to use the correct shell. The two most commonly used shells are sh and bash. The sh shell is the default shell on most Linux distributions, while the bash shell is the default on macOS.

To run a bash script using the sh shell, you would use the following command:

sh ./do_one_thing.sh

To run a bash script using the bash shell, you would use the following command:

bash ./do_another_thing.sh

It is important to note that using the wrong shell can result in unexpected behavior and potential security risks. Therefore, it is crucial to use the correct shell when running a bash script.

Naming Conventions

Naming conventions are important when it comes to running a bash script. The .sh extension is commonly used for bash scripts, but it can be risky if you have multiple scripts with similar names. For example, if you have two scripts named do_one_thing.sh and do_another_thing.sh, it can be easy to accidentally run the wrong script.

To avoid this issue, it is recommended to use a more descriptive naming convention. For example, you could name your script do_another_thing.bash instead of do_another_thing.sh. This provides an additional layer of protection against accidentally running the wrong script.

The Shebang Line

The shebang line is the first line of a bash script and specifies the shell that should be used to execute the script. For example, the following shebang line specifies that the script should be executed using the bash shell:

#!/bin/bash

The shebang line is important because it ensures that the script is executed using the correct shell. However, it is important to note that the shebang line can be overwritten if the script is executed using the sh shell.

To ensure that the script is executed using the correct shell, you can specify the shell explicitly when executing the script. For example, to execute a script using the bash shell, you would use the following command:

bash ./do_another_thing.sh

This ensures that the script is executed using the correct shell, regardless of the shebang line.

Setting Permissions

Before you can execute a bash script, you need to set the appropriate permissions. By default, bash scripts are not executable, so you need to set the executable bit on the file.

To set the executable bit on a bash script, you can use the following command:

chmod +x ./do_another_thing.sh

This sets the executable bit on the file, allowing you to execute the script.

Conclusion

In conclusion, running a bash script in the proper way is crucial to avoid potential security risks. This includes using the correct shell, using descriptive naming conventions, and setting the appropriate permissions. By following these best practices, you can ensure that your bash scripts are executed safely and securely.

The shebang line at the beginning of a script is used to specify the interpreter that should be used to execute the script. It should be the first line of the script and should start with a # followed by an exclamation mark (!) and the path to the interpreter executable.

For example, if you have a script that should be interpreted by the Bash shell, you would use the following shebang line:

#!/bin/bash

If you have a script that should be interpreted by the sh shell, you would use the following shebang line:

#!/bin/sh

If you have a script with a shebang line, you can run it directly by specifying the path to the script on the command line. For example, if you have a script named myscript.sh with the following shebang line:

#!/bin/bash

You can run it by typing:

./myscript.sh

It is not necessary to specify the interpreter on the command line. The system will recognize the shebang line and use the specified interpreter to execute the script.

As for the extension of the script file, it is not important for the script to have a specific extension. You can use any extension you like, or no extension at all. However, it is a good practice to use a standard extension such as .sh or .bash to indicate that the file is a shell script. This can make it easier for others to recognize the type of the file and know how to execute it.

In summary, you can run a shell script by specifying the path to the script on the command line, and the system will use the interpreter specified in the shebang line to execute the script. The extension of the script file is not important, but it is a good practice to use a standard extension to indicate the type of the file.

When I write a shebang at the top of my file, it defines what interpreter will be run when I run ./name_of_file (assuming it’s executable). For example, if I write the following code:

#!/bin/cat
test 123

it will simply print the above file when I run it with ./name_of_file, as it will run cat name_of_file. Similarly, if I write the following code:

#!/bin/echo
hello, world

it will simply print name_of_file, because it runs echo name_of_file. If I set the shebang to bash or sh, I can choose what interpreter it runs with, as long as I remember to invoke it with ./name_of_file. It’s worth noting that while using .sh for sh and .bash for bash works fine, it’s non-standard. File extensions are fairly fluid on Linux.