10-30-2001
dup()
Would anyone be so kind to explain to me the function of dup() in UNIX? As far as I am concerned, it duplicates a file descriptor. Under what circumstances would we need to duplicate a file descriptor in a UNIX environment?
Thank you.
vinchen
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LEARN ABOUT OPENSOLARIS
dup
dup(2) System Calls dup(2)
NAME
dup - duplicate an open file descriptor
SYNOPSIS
#include <unistd.h>
int dup(int fildes);
DESCRIPTION
The dup() function returns a new file descriptor having the following in common with the original open file descriptor fildes:
o same open file (or pipe)
o same file pointer (that is, both file descriptors share one file pointer)
o same access mode (read, write or read/write).
The new file descriptor is set to remain open across exec functions (see fcntl(2)).
The file descriptor returned is the lowest one available.
The dup(fildes) function call is equivalent to:
fcntl(fildes, F_DUPFD, 0)
RETURN VALUES
Upon successful completion, a non-negative integer representing the file descriptor is returned. Otherwise, -1 is returned and errno is set
to indicate the error.
ERRORS
The dup() function will fail if:
EBADF The fildes argument is not a valid open file descriptor.
EINTR A signal was caught during the execution of the dup() function.
EMFILE The process has too many open files (see getrlimit(2)).
ENOLINK The fildes argument is on a remote machine and the link to that machine is no longer active.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
|MT-Level |Async-Signal-Safe |
+-----------------------------+-----------------------------+
SEE ALSO
close(2), creat(2), exec(2), fcntl(2), getrlimit(2), open(2), pipe(2), dup2(3C), lockf(3C), attributes(5), standards(5)
SunOS 5.11 28 Dec 1996 dup(2)