| .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 /sys/src/libc/9syscall | |
| .SH SEE ALSO | |
| .IR intro (3), | |
| .IR dup (3) | |
| .SH DIAGNOSTICS | |
| Sets | |
| .IR errstr . |