Standard Input

Core Idea

Standard input is where commands read text when no filename is supplied.

Three common sources feed stdin:

• Your keyboard.
• A pipe from another command.
• A redirected file.

Practice Alone

Type input into read, then pipe text into commands that read stdin.

printf 'Type your name: '
read -r name
printf 'Hello, %s\n' "$name"

Pipe text into a command:

printf 'one\ntwo\nthree\n' | wc -l

Redirect a file into stdin:

wc -l < /etc/services

Watch Out

• A command may appear to hang because it is waiting for stdin. Press Ctrl-C if you need to stop it.
• read should usually use -r so backslashes are not treated specially.
• A pipe connects stdout from the left command to stdin of the right command.

Done When

You can explain why pipes and read both depend on stdin.

Docs Pointers

• Read read, pipes, stream redirection, and I/O.