dup, dup2

Duplicates an open file descriptor.

Syntax

   #include <unistd.h>

   int dup (int fildes);



   int dup2(iint fildes, int fildes2)

Parameters

fildes: An open file descriptor.

Return Values

>=0: Success. A new file descriptor is returned.
-1: An error occurred. the open file descriptor is not duplicated, and errno is set to indicate the error condition.

Description

The dup() and dup2 functions return the lowest numbered file descriptor not currentely open by the calling process. The file descriptors returned by dup() and dup2() refer to the same open file description as fildes and share any locks.

The dup() and dup2() functions ignore file access permission bits when attempting to duplicate an open file descriptor.

Implementation Considerations

Refer to the EEXCL and ESYSERR error descriptions below.

Signals generated for the calling process during execution of dup() re deferred from delivery until completion of this function.

Errors

If an error occurs, errno is set to one of the following values:

`EBADF`	CAUSE	The parameter `fildes` is not a valid open file descriptor.
	ACTION	Check to see if the value passed in `fildes` has been altered or whether the file indicated by `fildes` was ever opened.
`EEXCL`	CAUSE	The specified file descriptor is opened for exclusive access.
	ACTION	Do not attempt to duplicate a file descriptor that is opened for exclusive access.
`EMFILE`	CAUSE	The number of open files and directories would exceed `{OPEN_MAX}`, the limit of opened files per process.
	ACTION	Check process limit in `<limits.h>`. Close a file.
`ESYSERR`	CAUSE	An operating system error has occurred that does not map directly to any of the above errors.
	ACTION	Examine the MPE/iX error stack for the type of system error.

dup, dup2

Technical documentation

» Table of Contents

» Index