Bash Standard Streams

Understanding stdin, stdout, and stderr is fundamental for working effectively with the command line and writing scripts in bash or any other programming language. They provide a structured way to handle input, output, and errors, contributing to the reliability and efficiency of your programs.

Why are they important:

• Debugging: Having separate channels for normal output and errors helps in debugging. You can see what went wrong without cluttering the regular output.
• Pipeline: They allow for the chaining of commands in a pipeline, where the output of one command becomes the input of another.
• Flexibility: They provide flexibility in redirecting input and output streams, enabling automation and scripting.

Functionality:

• Redirecting: You can redirect stdin, stdout, and stderr to/from files, allowing you to save or read from specific sources.
• Piping: You can use pipes (|) to send the output of one command as input to another, utilizing stdin and stdout.
• Error Handling: stderr is particularly useful for capturing errors separately from regular output, helping identify and resolve issues efficiently.

Standard Input (stdin):

• What it is: stdin is where your program receives input from. It’s like a pipe through which you can pour information into your program.
• Analogical example: Imagine stdin as a kitchen sink’s faucet. You can pour water (input) into a glass (your program) through this faucet.

Standard Output (stdout):

• What it is: stdout is where your program sends its normal output. It’s like a conveyor belt where your program places its results or messages.
• Analogical example: Think of stdout as a printing machine. Your program writes messages on pieces of paper (output), and this machine prints them out for you to see.

Standard Error (stderr):

• What it is: stderr is where your program sends error messages or warnings. It’s a separate channel from stdout, specifically meant for errors.
• Analogical example: Consider stderr as a red warning light on a dashboard. When something goes wrong (an error), your program turns on this light to alert you, separate from the regular output.

grep foobar "$file" > /dev/null 2> /dev/null
# 2> represents the stderr stream, redirects STDOUT and STDERR to a null register