Skip to main content

File Descriptors: Input And Output Channels

File descriptors are channels. stdin. stdout. stderr. Understand them.

Here's the thing: File descriptors are channels. 0 is stdin. 1 is stdout. 2 is stderr. Learn them.

Standard Descriptors​

  • 0 = stdin (input)
  • 1 = stdout (output)
  • 2 = stderr (errors)

My take: Three standard descriptors. Learn them.

Redirecting​

command 1> output.log    # stdout
command 2> error.log    # stderr
command 0< input.txt   # stdin

My take: Redirect descriptors. Use numbers.

Custom Descriptors​

exec 3> custom.log
echo "Hello" >&3
exec 3>&-

My take: Custom descriptors are advanced. Use when needed.

Common Patterns​

Separate Outputs​

command > output.log 2> error.log

What's Next?​

Now that you understand descriptors, you can control I/O. Or review Input/Output to reinforce.

Personal note: File descriptors seemed complex at first. Then I learned: 0, 1, 2. Now I use them. They're useful. Learn them.