Mac OS X Tiger in a Nutshell

Redirection Forms

Table 5-20. I/O file descriptors

File descriptor	Name	Common abbreviation	Typical default
0	Standard input	stdin	Keyboard
1	Standard output	stdout	Screen
2	Standard error	stderr	Screen

The usual input source or output destination can be changed as shown in Table 5-21.

Table 5-21. I/O redirectors

Redirector	Function
> file	Direct standard output to file.
< file	Take standard input from file.
cmd1 | cmd2	Pipe; take standard output of cmd1 as standard input to cmd2.
>> file	Direct standard output to file; append to file if it already exists.
>| file	Force standard output to file even if noclobber is set.
n>| file	Force output from the file descriptor n to file even if noclobber is set.
<> file	Use file as both standard input and standard output.
<< text	Read standard input up to a line identical to text (text can be stored in a shell variable). Input is usually typed on the screen or in the shell program. Commands that typically use this syntax include cat, echo, ex, and sed. If text is enclosed in quotes, standard input will not undergo variable substitution, command substitution, etc.
n> file	Direct file descriptor n to file.
n< file	Set file as file descriptor n.
>&n	Duplicate standard output to file descriptor n.
<&n	Duplicate standard input from file descriptor n.
&>file	Direct standard output and standard error to file.
<&-	Close the standard input.
>&-	Close the standard output.
n>&-	Close ...