stdout (standard output)

Stream 1, where a program writes its normal results.

Standard output is stream 1, where a program writes its results. By default it goes to your terminal; redirect it to a file with > (replacing contents) or >> (appending), or into another program with a pipe.

Results and errors travel on separate streams by design, so you can save clean output to a file while still seeing errors on screen, or the reverse.

See it in practice

$ ls -l > listing.txt

Stream 1 goes to the file instead of the screen. The command is unaware: the shell rewired it before launch.

Where you'll meet it

stderr (standard error)

Stream 2: the separate channel for errors and diagnostics.

Redirection (> and >>)

Sending a program's streams to files instead of the screen.

tee

Split a stream: watch output live while saving a copy, and write files with sudo.

Learn these concepts by typing them: the interactive course builds them up lesson by lesson in a real simulated shell.