Shell Redirections ↔ Quick Guide

File descriptors:

• stdin : 0
• stdout : 1
• stderr : 2

Redirecting stdin

This trick can be used to take multi-line input in scripts.

#!/usr/bin/env bash

echo -e "Enter Commit Message (Ctrl+d when done):"
msg=$(</dev/stdin)
echo $msg

Redirecting stderr

1. Use 2>. Compatible with both bash and sh

Redirecting both stderr & stdout

1. With bash, use some_command &> /dev/null
2. With sh,

   some_command > where-to-redirect 2>&1
   # or
   some_command 2>&1 > stdout_and_err
   

3. If you want to capture standard output/error separately,

   $ some_command 1>output.txt 2>error.txt