Use of file descriptors
There are three types of I/O, which each have their own identifier, called a file descriptor:
standard output: 1
standard error: 2
In the following descriptions, if the file descriptor number is omitted, and the first character of the redirection operator is , the redirection refers to the standard output (file descriptor 1).
Some practical examples will make this more clear:
Will direct both standard output and standard error to the file dirlist, while the command
Will only direct standard output to dirlist. This can be a useful option for programmers.
ampersand is used to run a process in the background. Here, it merely serves as an indication that the number that follows is not a file name, but rather a location that the data stream is pointed to.
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