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 references 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 operating system, in a
structure that can be reference counted and garbage col-
lected. When the FD value is reclaimed, the system automat-
ically closes the associated integer file descriptor. There
are occasions when a program must access the underlying
integer file descriptor, such as when rearranging the stan-
dard 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 associated 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 descrip-
tor 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 ALSO
sys-intro(2), sys-open(2)
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