dup, fildes - duplicate an open file descriptor .EX include "sys.m"; sys := load Sys Sys->PATH; dup: fn(oldfd, newfd: int): int; fildes: fn(fd: int): ref FD; 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 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 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.

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 .

sys-intro (2), sys-open (2)