202 lines
4.7 KiB
Groff
202 lines
4.7 KiB
Groff
.\" $NetBSD: popen.3,v 1.15 2004/07/14 20:10:14 wiz Exp $
|
|
.\"
|
|
.\" Copyright (c) 1991, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" @(#)popen.3 8.2 (Berkeley) 5/3/95
|
|
.\"
|
|
.Dd July 14, 2004
|
|
.Dt POPEN 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm popen ,
|
|
.Nm pclose
|
|
.Nd process
|
|
.Tn I/O
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In stdio.h
|
|
.Ft FILE *
|
|
.Fn popen "const char *command" "const char *type"
|
|
.Ft int
|
|
.Fn pclose "FILE *stream"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn popen
|
|
function
|
|
.Dq opens
|
|
a process by creating an IPC connection,
|
|
forking,
|
|
and invoking the shell.
|
|
Historically,
|
|
.Nm popen
|
|
was implemented with a unidirectional pipe;
|
|
hence many implementations of
|
|
.Nm popen
|
|
only allow the
|
|
.Fa type
|
|
argument to specify reading or writing, not both.
|
|
Since
|
|
.Nm popen
|
|
is now implemented using sockets, the
|
|
.Fa type
|
|
may request a bidirectional data flow.
|
|
The
|
|
.Fa type
|
|
argument is a pointer to a null-terminated string
|
|
which must be
|
|
.Ql r
|
|
for reading,
|
|
.Ql w
|
|
for writing, or
|
|
.Ql r+
|
|
for reading and writing.
|
|
.Pp
|
|
The
|
|
.Fa command
|
|
argument is a pointer to a null-terminated string
|
|
containing a shell command line.
|
|
This command is passed to
|
|
.Pa /bin/sh
|
|
using the
|
|
.Fl c
|
|
flag; interpretation, if any, is performed by the shell.
|
|
.Pp
|
|
The return value from
|
|
.Fn popen
|
|
is a normal standard
|
|
.Tn I/O
|
|
stream in all respects
|
|
save that it must be closed with
|
|
.Fn pclose
|
|
rather than
|
|
.Fn fclose .
|
|
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
|
|
.Fn popen ,
|
|
unless this is altered by the command itself.
|
|
Conversely, reading from a
|
|
.Dq popened
|
|
stream reads the command's standard output, and
|
|
the command's standard input is the same as that of the process that called
|
|
.Fn popen .
|
|
.Pp
|
|
Note that output
|
|
.Fn popen
|
|
streams are fully buffered by default.
|
|
.Pp
|
|
The
|
|
.Fn pclose
|
|
function waits for the associated process to terminate
|
|
and returns the exit status of the command
|
|
as returned by
|
|
.Fn wait4 .
|
|
.Sh RETURN VALUES
|
|
The
|
|
.Fn popen
|
|
function returns
|
|
.Dv NULL
|
|
if the
|
|
.Xr fork 2 ,
|
|
.Xr pipe 2 ,
|
|
or
|
|
.Xr socketpair 2
|
|
calls fail,
|
|
or if it cannot allocate memory.
|
|
.Pp
|
|
The
|
|
.Fn pclose
|
|
function
|
|
returns \-1 if
|
|
.Fa stream
|
|
is not associated with a
|
|
.Dq popened
|
|
command, if
|
|
.Fa stream
|
|
has already been
|
|
.Dq pclosed ,
|
|
or if
|
|
.Xr wait4 2
|
|
returns an error.
|
|
.Sh ERRORS
|
|
The
|
|
.Fn popen
|
|
function does not reliably set
|
|
.Va errno .
|
|
.Sh SEE ALSO
|
|
.Xr sh 1 ,
|
|
.Xr fork 2 ,
|
|
.Xr pipe 2 ,
|
|
.Xr socketpair 2 ,
|
|
.Xr wait4 2 ,
|
|
.Xr fclose 3 ,
|
|
.Xr fflush 3 ,
|
|
.Xr fopen 3 ,
|
|
.Xr stdio 3 ,
|
|
.Xr system 3
|
|
.Sh STANDARDS
|
|
The
|
|
.Fn popen
|
|
and
|
|
.Fn pclose
|
|
functions conform to
|
|
.St -p1003.2-92 .
|
|
.Sh HISTORY
|
|
A
|
|
.Fn popen
|
|
and a
|
|
.Fn pclose
|
|
function appeared in
|
|
.At v7 .
|
|
.Sh BUGS
|
|
Since the standard input of a command opened for reading
|
|
shares its seek offset with the process that called
|
|
.Fn popen ,
|
|
if the original process has done a buffered read,
|
|
the command's input position may not be as expected.
|
|
Similarly, the output from a command opened for writing
|
|
may become intermingled with that of the original process.
|
|
The latter can be avoided by calling
|
|
.Xr fflush 3
|
|
before
|
|
.Fn popen .
|
|
.Pp
|
|
Failure to execute the shell
|
|
is indistinguishable from the shell's failure to execute command,
|
|
or an immediate exit of the command.
|
|
The only hint is an exit status of 127.
|
|
.Pp
|
|
The
|
|
.Fn popen
|
|
argument
|
|
always calls
|
|
.Xr sh 1 ,
|
|
never calls
|
|
.Xr csh 1 .
|