How to use the command 'unset' (with examples)

The unset command is used to remove shell variables or functions. It allows you to remove variables or functions that are no longer needed in your shell environment.

Use case 1: Remove the variable foo, or if the variable doesn’t exist, remove the function foo

Code:

unset foo

Motivation: You may want to remove a variable foo from your shell environment if you no longer need it. This can help to clean up your environment and avoid any potential conflicts or confusion with other variables.

Explanation: The unset command is followed by the name of the variable or function you want to remove. In this case, the command unset foo removes the variable foo from the shell environment.

Example output:

$ echo $foo
foo: Undefined variable

In this example, the variable foo is accessed using the echo command after it has been unset. The output shows that the variable foo is undefined, indicating that it has been successfully removed.

Use case 2: Remove the variables foo and bar

Code:

unset -v foo bar

Motivation: If you have multiple variables that you want to remove at once, you can use the unset command with the -v option followed by the names of the variables you want to remove. This can save time and make the cleanup process more efficient.

Explanation: The -v option is used to unset shell variables. The command unset -v foo bar removes both the variables foo and bar from the shell environment.

Example output:

$ echo $foo
foo: Undefined variable
$ echo $bar
bar: Undefined variable

After running the unset -v foo bar command, accessing the variables foo and bar using the echo command shows that both variables are undefined, indicating that they have been successfully removed.

Use case 3: Remove the function my_func

Code:

unset -f my_func

Motivation: If you have defined a function in your shell environment but no longer need it, you can use the unset command with the -f option followed by the name of the function to remove it. This helps to clean up your environment and frees up system resources.

Explanation: The -f option is used to unset shell functions. The command unset -f my_func removes the function my_func from the shell environment.

Example output:

$ my_func
my_func: command not found

After running the unset -f my_func command, attempting to invoke the function my_func results in a “command not found” error. This indicates that the function has been successfully removed.

Conclusion:

The unset command provides a convenient way to remove shell variables or functions that are no longer needed. By using the appropriate options and arguments, you can efficiently clean up your shell environment and avoid any potential conflicts or confusion.