A/UX® System Administrator's Reference Sections 1M, 7, and 8

StartupShell(8) StartupShell(8)
ments to the invoked program. Each of the constructions affects
processing as described in the following list
word
»word
< & digit
Use file word as standard output (file descriptor
1). If the file does not exist, it is created; otherwise,
it is truncated to a length of O.
Use file word as standard output. If the file exists,
output is appended to it (by first seeking to
the end-of-file); otherwise, the file is created.
Use the file associated with file descriptor digit
as standard input. Similarly, >&digit uses the
file associated with the file descriptor digit as the
standard output
< & - The standard input is closed. Similarly, standard
output is closed by using> & -.
If any of the above are preceded by a digit, the file descriptor is
specified by the digit (instead of the default 0 or 1). For example:
... 2>&1
associates file descriptor 2 with the file currently associated with
file descriptor 1.
The order in which redirections are specified is significant. The
shell evaluates redirections from left to right. For example,
... l>word 2>&1
first associates file descriptor 1 with file word. It associates file
descriptor 2 with the file associated with file descriptor 1 (word).
If the order of redirections were reversed, file descriptor 2 would
be associated with the terminal (assuming file descriptor 1 had
been) and file descriptor 1 would be associated with file word.
The environment passed to an executing program contains the
same file descriptors as the shell, except those modified by input
and output redirections on the command line.
Built-in Commands
Built-in commands do not invoke corresponding programs that reside
in a file system. Rather, the shell interprets such commands
and their arguments all by itself. For these built-in commands, input
and output redirection is permitted. Without redirection, the
February, 1990
Revision C
5