2.9BSD/usr/man/cat2/dup.2

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DUP(2)              UNIX Programmer's Manual               DUP(2)

NAME
     dup, dup2 - duplicate an open file descriptor

SYNOPSIS
     dup(fildes)
     int fildes;

     dup2(fildes, fildes2)
     int fildes, fildes2;

DESCRIPTION
     Given a file descriptor returned from an _o_p_e_n, _p_i_p_e, or
     _c_r_e_a_t(2) call, _d_u_p allocates another file descriptor
     synonymous with the original.  The new file descriptor is
     returned.

     In the second form of the call, _f_i_l_d_e_s is a file descriptor
     referring to an open file, and _f_i_l_d_e_s_2 is a non-negative
     integer less than the maximum value allowed for file
     descriptors (approximately 19).  _D_u_p_2 causes _f_i_l_d_e_s_2 to
     refer to the same file as _f_i_l_d_e_s. If _f_i_l_d_e_s_2 already
     referred to an open file, it is closed first.

RETURN VALUE
     Upon successful completion, a value of 0 is returned.  Oth-
     erwise, a value of -1 is returned and _e_r_r_n_o is set to indi-
     cate the error.

ERRORS
     _D_u_p and _d_u_p_2 will fail if:

     [EBADF]             _F_i_l_d_e_s  _o_r  _f_i_l_d_e_s_2 is not a valid
                         active descriptor.

     [EMFILE]            Too many descriptors are active.

SEE ALSO
     close(2), creat(2), open(2), pipe(2)

ASSEMBLER
     (dup = 41.)
     (file descriptor in r0)
     (new file descriptor in r1)
     sys dup
     (file descriptor in r0)

     The _d_u_p_2 entry is implemented by adding 0100 to _f_i_l_d_e_s.

Printed 5/23/83                                                 1