How to pipe output and duplicate it to STDOUT?



As an IT administrator, it is important to ensure that the systems you are responsible for are running smoothly and efficiently. Unfortunately, there are times when problems arise that require you to take action and investigate the issue further. One way to do this is by using pipes and redirecting the output of a command to both the terminal window and a file. This allows you to review the output of a command while also having a record of the output stored in a file.

A pipe is a mechanism in Linux and Unix-like operating systems that allows the output of one command to be used as the input of another command. Pipes are typically represented by the | symbol and are used to connect two commands. For example, you can use a pipe to connect the output of the ls command, which lists the files in a directory, to the less command, which displays the output of the ls command one page at a time.

When you are troubleshooting an issue, you may want to review the output of a command and also save it to a file for later review. To do this, you can use the tee command, which reads from standard input (stdin) and writes to standard output (stdout) as well as one or more files. This allows you to view the output of a command in the terminal window and also have the output saved in a file.

To use the tee command, you must first pipe the output of the command you are running to the tee command. For example, if you wanted to view the output of the ls command and also save it to a file, you could use the following command:

ls | tee output.txt

This command would redirect the output of the ls command to both the terminal window and the output.txt file. You can also use the tee command with other commands, such as grep, to filter the output and save the filtered output to a file. For example, if you wanted to list all of the files in a directory that have the word “test” in their name, you could use the following command:

ls | grep test | tee output.txt

This command would pipe the output of the ls command to the grep command, which would filter the output and only show files that have the word “test” in their name. The output of the grep command would then be piped to the tee command, which would write the filtered output to both the terminal window and the output.txt file.

Using the tee command is a great way to both view the output of a command and save it to a file for later review. This can be especially useful when you are troubleshooting an issue or trying to debug a problem. Being able to review the output of a command can help you quickly identify the cause of a problem and take the appropriate steps to resolve it.

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