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. 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 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 uses the integer file descriptor fd to create a new Limbo file descriptor, suitable for other Sys module func- tions. It returns nil if it cannot convert fd. SEE ALSO sys-intro(2), sys-open(2)