DUP(II) 8/5/73 DUP(II)
NAME
dup - duplicate an open file descriptor
SYNOPSIS
(dup = 41.; not in assembler)
(file descriptor in r0)
sys dup
dup(fildes)
int fildes;
DESCRIPTION
Given a file descriptor returned from an open, pipe, or
creat call, dup will allocate another file descriptor
synonymous with the original. The new file descriptor is
returned in r0.
Dup is used more to reassign the value of file descriptors
than to genuinely duplicate a file descriptor. Since the
algorithm to allocate file descriptors returns the lowest
available value, combinations of dup and close can be used
to manipulate file descriptors in a general way. This is
handy for manipulating standard input and/or standard
output.
SEE ALSO
creat (II), open (II), close (II), pipe (II)
DIAGNOSTICS
The error bit (c-bit) is set if: the given file descriptor
is invalid; there are already too many open files. From C,
a -1 returned value indicates an error.