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System User's Guide: Operating System and Devices
Input and Output Redirection in the Bourne Shell
In general, most commands do not know whether their
input or output is associated with the keyboard, the display screen, or a
file. Thus, a command can be used conveniently either at the keyboard or in
a pipeline.
The following redirection options can appear anywhere
in a simple command. They can also precede or follow a command, but are not
passed to the command.
<File |
Uses the specified file as standard input. |
>File |
Uses the specified file as standard output. Creates the file if it
does not exist; otherwise, truncates it to zero length. |
> >File |
Uses the specified file as standard output. Creates the file if it
does not exist; otherwise, adds the output to the end of the file. |
<<[-]eofstr |
Reads as standard input all lines from the eofstr variable up to a line containing only eofstr or
up to an end-of-file character. If any character in the eofstr variable is quoted, the shell does not expand or interpret any
characters in the input lines. Otherwise, it performs variable and command
substitution and ignores a quoted newline character (\newline). Use a \ to quote characters within the eofstr variable or within the input lines.
If you add
a - to the << redirection option, then all leading tabs are stripped
from the eofstr variable and from the input lines. |
<&Digit |
Associates standard input with the file descriptor specified by the Digit variable. |
>&Digit |
Associates standard output with the file descriptor specified by
the Digit variable. |
<&- |
Closes standard input. |
>&- |
Closes standard output. |
Note: The restricted
shell does not allow output redirection.
For more information about redirection, see Input and Output Redirection.
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