exec MacOS Command Guide

The MacOS exec command is a powerful tool for managing processes and executing shell scripts. By using the exec command, you can replace the current process image with a new process, effectively running the new process in place of the old one. This can be especially useful for optimizing resource usage and improving the performance of your system. Additionally, the exec command allows you to pass arguments to the new process, making it a versatile tool for various tasks. Mastering the exec command can help you streamline your workflow and improve your efficiency when working in the MacOS terminal.

exec Syntax:

exec [option] [parameter]

Options:

Option	Description
-l	This option uses a login shell.
-a	This option allows specifying the argument to be passed to the command.
-c	This option specifies the command to execute.

Parameters:

Parameter	Description
command	The command or script to be executed.
argument	The argument to be passed to the command.

Caution

Exercise caution when using the exec command as it can replace the current process with a new one, potentially leading to loss of unsaved data or unexpected behavior.

exec Command Samples:

Execute a Shell Command

exec ls -l

Executes the “ls -l” command in the current shell session.

Use exec to Replace the Current Process

exec echo "Replacing current process"

Replaces the current process with the “echo” command to display the message.

Redirect Output to a File with exec

exec ls -l > output.txt

Executes the “ls -l” command and redirects the output to a file named “output.txt”.

Execute a Script with exec

exec ./script.sh

Executes the shell script named “script.sh” with the exec command.

Close File Descriptors with exec

exec 3> output.txt
exec 3>&-

Opens a file descriptor to “output.txt” and then closes it using the exec command.

Execute a Command Using exec with Custom Environment Variables

exec -a "CustomProcessName" ./process

Executes the “./process” command with a custom name “CustomProcessName” using the exec command.

Replace Current Shell with Another Shell using exec

exec /bin/bash

Replaces the current shell with a new instance of the bash shell using the exec command.

Tip

When using the exec command in MacOS, it’s important to understand that it replaces the current shell with the specified command, meaning that any commands after exec will not be executed. Make sure to review the command thoroughly before using exec to prevent unexpected behavior.

How do I use exec in MacOS?

To use the exec command in MacOS, execute the following command:

exec --option <value>

How can I execute a new command with exec in MacOS?

To execute a new command with the exec command in MacOS, use the following syntax:

exec command argument

Can I use multiple commands with exec in MacOS?

No, using multiple commands with exec in MacOS is not possible as it replaces the current shell process with the specified command.

How does exec handle exit codes in MacOS?

When using exec in MacOS, the exit code of the command executed will become the exit code of the shell process.

Is it possible to use shell built-in commands with exec in MacOS?

Yes, you can use shell built-in commands with exec in MacOS. For example, to launch a new instance of the default shell, you can use the following:

exec bash

What is the difference between exec and command in MacOS?

In MacOS, exec is used to replace the current shell process with a new command, while command is a shell built-in that is used to execute commands without performing alias expansion or shell functions.

Applications of the exec command

• Replaces the current process with a new process
• Used to run a new command in the same process ID as the shell