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CHAPTER 6 Special Unix Features

6.1 File Descriptors

There are 3 standard file descriptors:

  • stdin 0 Standard input to the program

  • stdout 1 Standard output from the program

  • stderr 2 Standard error output from the program

Normally input is from the keyboard or a file. Output, both stdout and stderr, normally go to the terminal, but you can redirect one or both of these to one or more files.

You can also specify additional file descriptors, designating them by a number 3 through 9, and redirect I/O through them.

Introduction to Unix - 14 AUG 1996
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