dup - duplicate an open file descriptor

dup: fn(oldfd, newfd: int): int;

## returns an integer file descriptor, or -1 if 
unsuccessful.

Description

The dup function takes a valid integer file descriptor, oldfd, referring to an open file, and returns a new integer file descriptor referring to the same file. If newfd is in the range of legal file descriptors, dup will use that for the new file descriptor (closing any old file associated with newfd). If newfd is -1, the system chooses the lowest available file descriptor. If a suitable file descriptor cannot be found, dup returns -1.

Example

output: ref sys->FD;
output = sys->open("outfile", sys->OWRITE);
stdout := sys->dup(output.fd, 1);

See Also

System Module Overview

open, create - open/create a file for reading or writing