Glossary
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.txtStream 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.
teeSplit 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.