Redirection (computing)

The concept of redirection is quite old, dating back to the earliest operating systems (OS).

[citation needed] A discussion of the design goals for redirection can be found already in the 1971 description of the input-output subsystem of the Multics OS.

[1] However, prior to the introduction of UNIX OS with its "pipes", redirection in operating systems was hard or even impossible to do.

Dr. Alexia Massalin's experimental operating system, Synthesis, would adjust the priority of each task as they ran according to the fullness of their input and output buffers.

[4] This produces the same end result as using two redirects and a temporary file, as in: But here, command2 does not start executing until command1 has finished, and a sufficiently large scratch file is required to hold the intermediate results as well as whatever work space each task required.

This runs the ftp client with input user, press return, then pass.

In casual use, the initial step of a pipeline is often cat or echo, reading from a file or string.

Executed without redirection, it will output hits to stdout and errors (e.g. for lack of privilege to traverse protected directories) to stderr.

If standard output is directed to file results, error messages appear on the console.