4.4BSD/usr/share/man/cat3/pclose.0

POPEN(3)                    BSD Programmer's Manual                   POPEN(3)

NNAAMMEE
     ppooppeenn, ppcclloossee - process I/O

SSYYNNOOPPSSIISS
     ##iinncclluuddee <<ssttddiioo..hh>>

     _F_I_L_E _*
     ppooppeenn(_c_o_n_s_t _c_h_a_r _*_c_o_m_m_a_n_d, _c_o_n_s_t _c_h_a_r _*_t_y_p_e);

     _i_n_t
     ppcclloossee(_F_I_L_E _*_s_t_r_e_a_m);

DDEESSCCRRIIPPTTIIOONN
     The ppooppeenn() function ``opens'' a process by creating a pipe, forking, and
     invoking the shell.  Since a pipe is by definition unidirectional, the
     _t_y_p_e argument may specify only reading or writing, not both; the result-
     ing stream is correspondingly read-only or write-only.

     The _c_o_m_m_a_n_d argument is a pointer to a null-terminated string containing
     a shell command line.  This command is passed to _/_b_i_n_/_s_h using the --cc
     flag; interpretation, if any, is performed by the shell.  The _m_o_d_e argu-
     ment is a pointer to a null-terminated string which must be either `r'
     for reading or `w' for writing.

     The return value from ppooppeenn() is a normal standard I/O stream in all re-
     spects save that it must be closed with ppcclloossee() rather than ffcclloossee().
     Writing to such a stream writes to the standard input of the command; the
     command's standard output is the same as that of the process that called
     ppooppeenn(), unless this is altered by the command itself.  Conversely, read-
     ing from a ``popened'' stream reads the command's standard output, and
     the command's standard input is the same as that of the process that
     called ppooppeenn().

     Note that output ppooppeenn() streams are fully buffered by default.

     The ppcclloossee() function waits for the associated process to terminate and
     returns the exit status of the command as returned by wwaaiitt44().

RREETTUURRNN VVAALLUUEE
     The ppooppeenn() function returns NULL if the fork(2) or pipe(2) calls fail,
     or if it cannot allocate memory.

     The ppcclloossee() function returns -1 if _s_t_r_e_a_m is not associated with a
     ``popened'' command, if _s_t_r_e_a_m already ``pclosed'', or if wait4 returns
     an error.

EERRRROORRSS
     The ppooppeenn() function does not reliably set _e_r_r_n_o.

SSEEEE AALLSSOO
     fork(2),  sh(1),  pipe(2),  wait4(2),  fflush(3),  fclose(3),  fopen(3),
     stdio(3),  system(3)

BBUUGGSS
     Since the standard input of a command opened for reading shares its seek
     offset with the process that called ppooppeenn(), if the original process has
     done a buffered read, the command's input position may not be as expect-
     ed.  Similarly, the output from a command opened for writing may become
     intermingled with that of the original process.  The latter can be avoid-
     ed by calling fflush(3) before ppooppeenn().

     Failure to execute the shell is indistinguishable from the shell's fail-
     ure to execute command, or an immediate exit of the command.  The only
     hint is an exit status of 127.

     The ppooppeenn() argument always calls sh,  never calls csh.

HHIISSTTOORRYY
     A ppooppeenn() and a ppcclloossee() function appeared in Version 7 AT&T UNIX.

4.4BSD                           June 4, 1993                                2