Working with Stdin, Stdout, and Stderr

As a system administrator or developer, using standard streams for scripting, automation, error handling, and managing system resources is one common task in your day-to-day life.

In this section, we have crafted examples to demonstrate various ways to work with stdin, stdout, and stderr, in Runme.

Reading from stdin and writing to stdout:

$ cat
Enter your text here.
^D

In this example, cat is invoked without any arguments, so it waits for input from stdin. After entering text and pressing ^D (Ctrl+D), it writes the input to stdout.

Redirecting stdin and stdout:

$ cat < input.txt > output.txt

Here, cat reads from input.txt (redirected stdin) and writes to output.txt (redirected stdout).

Appending to an Existing File:

$ echo "New content." >> existing_file.txt

This appends the text "New content." to the file existing_file.txt.

Redirecting stderr:

$ ls non_existent_dir 2> error_log.txt

If ls encounters an error (like trying to list a non-existent directory), the error message will be redirected to error_log.txt.

Redirecting stderr to stdout:

$ ls non_existent_dir 2>&1

This redirects both stderr and stdout to the same destination, which is typically the terminal.

Piping Output:

$ ls | grep ".txt"

This pipes the output of ls (which lists files and directories) to grep, which filters lines containing ".txt".

Redirecting stdout and stderr to Different Files:

$ myprogram > output.log 2> error.log

This runs myprogram, directing stdout to output.log and stderr to error.log, allowing for separate logging of standard output and error messages.

If you encounter any challenges with these practices, please don't hesitate to reach out to us. We would be glad to assist you.