When we say a command ``prints'' a value we typically mean that it displays the value on your terminal screen. What's really happening is that the result of the command is being sent to ``standard output'' (stdout), which by default is your screen. Similarly, ``standard input'' (stdin) is by default your keyboard. Data moving from the standard input to the standard output is an example of an I/O stream. It is possible to divert such streams to a certain extent. The following table summarizes the most common stream controls used in the csh environment with some examples:
| Operator | Function | Example | Description |
|---|---|---|---|
| < | redirect stdin | mail dcr < myfile | mail dcr the contents of myfile |
| > | redirect stdout | myprog > log | write output from myprog to log |
| » | append stdout | myprog » log | append output from myprog to log |
| « word | redirect stdin until word | myprog « STOP | send next lines to myprog until STOP |
| | | pipe stdout to stdin | echo test | lpr | send phrase ``test'' to printer |
There are also modifiers like >& (to redirect both stdout and ``standard error'' (stderr), the diagnostic stream) and >! (to ``clobber'' an existing output file without confirmation).