| .TH DUP 3 |
| .SH NAME |
| dup \- duplicate an open file descriptor |
| .SH SYNOPSIS |
| .B #include <u.h> |
| .br |
| .B #include <libc.h> |
| .PP |
| .B |
| int dup(int oldfd, int newfd) |
| .SH DESCRIPTION |
| Given a file descriptor, |
| .IR oldfd , |
| referring to an open file, |
| .I dup |
| returns a new file descriptor referring to the same file. |
| .PP |
| If |
| .I newfd |
| is \-1 the system chooses the lowest available file descriptor. |
| Otherwise, |
| .I dup |
| will use |
| .I newfd |
| for the new file descriptor |
| (closing any old file associated with |
| .IR newfd ). |
| File descriptors are allocated dynamically, |
| so to prevent unwarranted growth of the file descriptor table, |
| .I dup |
| requires that |
| .I newfd |
| be no greater than 20 more than the highest file descriptor ever used by |
| the program. |
| .SH SOURCE |
| .B /usr/local/plan9/src/libc/9syscall |
| .SH SEE ALSO |
| .IR intro (3), |
| .IR dup (3) |
| .SH DIAGNOSTICS |
| Sets |
| .IR errstr . |
