Function DUP2

Syntax

dup2 file-descriptor copy => error

Arguments and values

file-descriptor -- A non-negative fixnum.

copy -- A non-negative fixnum.

error -- A fixnum.

Description

This function makes copy be a copy of file-descriptor, closing copy first if necessary. However:

• If file-descriptor is not a valid file descriptor, the call fails and copy is not closed.
• If file-descriptor is a valid file descriptor, and copy has the same value as file-descriptor, then dup2 does nothing, and returns copy.

After a successful return from this system call, the old and new file descriptors may be used interchangeably. They refer to the same open file description (see open) and thus share file offset and file status flags; for example, if the file offset is modified by using lseek on one of the descriptors, the offset is also changed for the other.

The two descriptors do not share file descriptor flags (the close-on-exec flag). The close-on-exec flag (FD_CLOEXEC; see fcntl) for the duplicate descriptor is off.

Errors