Execute

The .sh extension is not necessary but is common when the script contains Bash or ZSH code.

Summary

• Run executable.

    $ ./my_script.sh
  

• Pass script name to bash command.

    $ bash my_script.sh
  

• Run source code in current process.

    $ source my_script.sh
  

• Pass contents of a file to bash with no args.

    $ cat script.sh | bash -
  

• Redirect in

    $ bash < my_script.sh
  

Source

This will run the content of the given script inside the parent shell. The target script should be a shell script and does not have to be executable.

Use the source command to persist changes from a script, such as changing directories, setting variables or activating a virtual environment.

• persist.sh

    echo 'Hello, world!'
    cd ~/Documents
    pwd
  

$ source persist.sh

Note that . is an alias for source.

$ . persist.sh

If you use using /bin/sh (such as in a Makefile or cronjob), on Ubuntu that dash. Which means you cannot use source and also you need to make the path relative. So use this:

$ . ./persist.sh

You can use arguments too.

$ source persist.sh foo bar

Execute with subshell

This will not persist any changes.

$ bash script.sh

e.g.

• script.sh

    echo 'Hello, world!'
    cd ~/Documents
    pwd
  

$ cd ~/Downloads
$ bash script.sh
Hello, world!
/my-user/home/Documents
$ pwd
/my-user/home/Downloads

Execute directly

This requires the file to be executable.

Scripts

The file can be any language (Python, JS, Bash) as long it has an appropriate shebang or the parent shell matches.

• file.sh

    echo 'Hello, world!'
  

$ chmod+ x file.sh

$ ./file.sh

If no shebang is set, then the script will be executed using the parent shell.

If you set a shebang then that will be used.

e.g.

• my_executable.sh

    #!/bin/bash
  
    echo 'Hello from the Bash world!'
  

• my_executable.py

    #!/usr/bin/env python3
  
    print('Hello from the PY world!')
  

$ ./my_executable.sh
Hello from the Bash world!
$ ./my_executable.py
Hello from the PY world!

Binary executables

The file can also be a binary compiled from a C or Go program. It is not easily readable as a text file but can be executable.

$ ./compiled
Hello, world!