Many operating systems have a command line that supports piped input and output.

Programs that consume input from the standard input, stdin, can be executed such that the input is redirected from a file instead of from the keyboard.

Programs that produce output to the standard output, stdout, can be executed such that the output is redirected to a file instead of to the screen.

There is also a standard error, stderr, output pipe.

Whenever typing input into a program, the following keys simulate the end of file for stdin.

• Windows: Type Ctrl-Z and press Enter.
• Linux: Type Ctrl-D.

The following are standard redirection characters.

• The standard input redirection is "<" (less-than sign).
• The standard output redirection is ">" (greater-than sign).
• The standard output append redirection is ">>".
• The standard error redirection is "2>".

In Linux (and Windows) the vertical bar character "|" is used to take the output of one program and use it for input to the next program (on the command line).

Note the use of the redirection character ">" to output to a file.

Likewise, programs that take input from the standard input can have input redirected from a file by using the redirection character "<". The Python executable supports redirection to both the standard output and standard error pipes from the command line. Here is the general form of the command.

For historical reasons, stream 2, as in redirection using "2>" is the standard output.