Standard Error in bash

In Bash, the standard error (stderr) is a file descriptor used for error output. By default, stderr is directed to the terminal along with the standard output (stdout). However, there are several ways to work with stderr in Bash:

  1. Redirecting stderr to a file: To redirect stderr to a file, you can use the 2> operator followed by the filename. For example:
command 2> error.log

This redirects the error output generated by command to the file error.log.

2. Appending stderr to a file: If you want to append stderr to a file instead of overwriting it, you can use the 2>> operator:

command 2>> error.log

This appends the error output to the existing contents of error.log, or creates the file if it doesn’t exist.

3. Discarding stderr: If you want to discard stderr and prevent it from being displayed or stored, you can redirect it to /dev/null:

command 2> /dev/null

This sends the error output to the special device file /dev/null, effectively discarding it.

4. Combining stdout and stderr: By default, both stdout and stderr are displayed on the terminal. You can use the 2>&1 operator to redirect stderr to the same destination as stdout:

command > output.txt 2>&1

This redirects both stdout and stderr to the file output.txt.

5. Displaying stderr separately: If you want to display stderr separately from stdout, you can redirect stderr to the terminal while redirecting stdout to a file:

command > output.txt 2>&1 | tee error.log

This redirects stdout to output.txt and displays stderr on the terminal using tee, while also saving stderr to error.log.

By understanding these techniques, you can effectively manage and handle error output (stderr) in your Bash scripts, allowing you to log errors, discard them, or display them separately as needed.

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