Running a Shell Script from the Command Line

Once you have created a shell script and given it execute permission, you can run it like any other program. The key detail is that Unix only finds programs automatically if they are located in a directory listed in your PATH environment variable. Your training scripts (like welcome) usually live in your home directory, so you must run them using an explicit path.

If your script is in your current working directory, typing its filename by itself usually fails:

% welcome
welcome: not found

This happens because the current directory (.) is normally not included in PATH for security reasons.

To run a script that is in the current directory, prefix it with ./:

% ./welcome

If execute permission is set, the script runs immediately using the interpreter specified on the first line (the shebang), such as #!/bin/sh.

Another common method is to call the interpreter directly and pass the script as an argument:

% sh ./welcome

This is useful when:

• You want to ensure a specific shell is used (for example sh vs bash).
• The script is not executable yet (you can still run it with sh script).
• You want to debug execution (for example, some shells support flags like -x to trace commands).

In practice, if your script starts with #!/bin/sh and has execute permission, using ./welcome is the cleanest workflow.

If you want to run your scripts without typing ./, place them in a directory that is already in your PATH, or create a personal scripts directory such as $HOME/bin and add it to your PATH.

Best practice is to avoid adding the current directory (.) to PATH, because it can allow unintended programs to run if a malicious or accidental filename matches a command you type.

• Permission denied: add execute permission (for example chmod u+x welcome).
• not found: run with ./welcome or provide the full/relative path.
• bad interpreter: the shebang path is wrong or the file has Windows CRLF line endings—convert to Unix LF.

Click the Quiz link below to test your knowledge of file permissions and script execution.
Shell Script File Permissions - Quiz
The next lesson wraps up what you have learned in this module.