1 .TH DUP 3
2 .SH NAME
3 dup \- duplicate an open file descriptor
4 .SH SYNOPSIS
5 .B #include <u.h>
6 .br
7 .B #include <libc.h>
8 .PP
9 .B
10 int dup(int oldfd, int newfd)
11 .SH DESCRIPTION
12 Given a file descriptor,
13 .IR oldfd ,
14 referring to an open file,
15 .I dup
16 returns a new file descriptor referring to the same file.
17 .PP
18 If
19 .I newfd
20 is \-1 the system chooses the lowest available file descriptor.
21 Otherwise,
22 .I dup
23 will use
24 .I newfd
25 for the new file descriptor
26 (closing any old file associated with
27 .IR newfd ).
28 File descriptors are allocated dynamically,
29 so to prevent unwarranted growth of the file descriptor table,
30 .I dup
31 requires that
32 .I newfd
33 be no greater than 20 more than the highest file descriptor ever used by
34 the program.
35 .SH SOURCE
36 .B /usr/local/plan9/src/libc/9syscall
37 .SH SEE ALSO
38 .IR intro (3),
39 .IR dup (3)
40 .SH DIAGNOSTICS
41 Sets
42 .IR errstr .