SYS-DUP(2)SYS-DUP(2)NAME
dup, fildes - duplicate an open file descriptor
SYNOPSIS
include "sys.m";
sys := load Sys Sys->PATH;
dup: fn(oldfd, newfd: int): int;
fildes: fn(fd: int): ref FD;
DESCRIPTION
The Limbo programming language and its libraries manage I/O via refer‐
ences to instances of abstract data type, FD, called a Limbo file
descriptor, or simply `file descriptor' when the context is understood.
FD holds an integer-valued file descriptor, the form used by the oper‐
ating system, in a structure that can be reference counted and garbage
collected. When the FD value is reclaimed, the system automatically
closes the associated integer file descriptor. There are occasions
when a program must access the underlying integer file descriptor, such
as when rearranging the standard input and output for a new subprocess.
The dup call 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 associ‐
ated with newfd); if newfd is -1 the system chooses the lowest avail‐
able file descriptor. If a suitable file descriptor cannot be found,
dup returns -1.
Fildes duplicates the integer file descriptor fd, as if by
sys->dup(fd,-1), and returns a reference to the new descriptor as an FD
value, making it usable by other functions in Sys, such as sys-print(2)
and sys-read(2). (Note that as described above, the newly-allocated
file descriptor will be closed automatically when the FD value is
reclaimed.) Fildes returns nil if it cannot duplicate fd.
SEE ALSOsys-intro(2), sys-open(2)SYS-DUP(2)
