Standard Streams

Each executable has associated with it three input/output streams: standard input , standard error , and standard output. Normally these streams come from or go to your console (i.e. your terminal).

Most Unix commands read from standard input and/or write to standard output.

These I/O streams are often represented as stdin, stderr, and stdout.

The Unix commands we have studied so far all write to standard output.

ls -l

produces output to the terminal.