git: 9front

ref: 38d3a8a38b0cd7b2b4c159c1fb68c3c0622f00c0
dir: /sys/man/2/dup/

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.TH DUP 2
.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.
.PP
.I Dup
does not copy the per file descriptor
.B OCEXEC
flag,
meaning that
.I newfd
will not be closed on
.IR exec (2)
syscall,
when
.I oldfd
had been previously opend with it.
.SH SOURCE
.B /sys/src/libc/9syscall
.SH SEE ALSO
.IR intro (2),
.IR dup (3)
.SH DIAGNOSTICS
Sets
.IR errstr .