Zsh: stdout and stderr both to console AND log

Zsh: stdout and stderr both to console AND log

If you are new to using the Zsh shell, you might have encountered situations where you need to see both the standard output (stdout) and the standard error (stderr) messages on your console while also logging them to a file. This article will guide you through the process of achieving this in a simple and easy-to-understand manner.

Understanding stdout and stderr

Before we dive into the solution, let's quickly understand what stdout and stderr are:

• Standard Output (stdout): This is the default output stream where the regular program output is displayed. It includes the normal information, warnings, and other messages.
• Standard Error (stderr): This stream is used to display error messages and any other diagnostic information that the program needs to communicate.

Redirecting stdout and stderr to console

To see both stdout and stderr messages on your console, you can use the following command:

command 2>&1

Let's break down the command:

• command: Replace this with the actual command you want to execute.
• 2>&1: This part redirects the stderr (file descriptor 2) to the same location as stdout (file descriptor 1), which is the console.

By using this command, both stdout and stderr messages will be displayed on your console.

Redirecting stdout and stderr to a log file

To log both stdout and stderr messages to a file, you can modify the previous command as follows:

command > output.log 2>&1

Here's what the modified command does:

• command: Replace this with the actual command you want to execute.
• > output.log: This part redirects the stdout (file descriptor 1) to the file named "output.log". If the file doesn't exist, it will be created. If it already exists, the new output will be appended to the existing content.
• 2>&1: This part redirects the stderr (file descriptor 2) to the same location as stdout (file descriptor 1), which is the log file.

With this modified command, both stdout and stderr messages will be displayed on your console, and at the same time, they will be logged to the specified log file.

Example usage

Let's consider a practical example to illustrate the usage of the commands mentioned above. Suppose you have a script called "backup.sh" that performs a backup of your important files. You want to see the progress and any error messages on your console while also saving them to a log file called "backup.log".

./backup.sh > backup.log 2>&1

By executing this command, the "backup.sh" script will run, and you will see the progress and any error messages on your console. Simultaneously, all the output will be logged to the "backup.log" file.

Conclusion

Redirecting both stdout and stderr messages to both the console and a log file can be extremely useful for monitoring and troubleshooting purposes. By following the simple commands mentioned in this article, you can achieve this easily in the Zsh shell.