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.\" Copyright (c) 1990, 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the American National Standards Committee X3, on Information
.\" Processing Systems.
.\"
.\" 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.
.\"
.\" $OpenBSD: system.3,v 1.14 2016/02/05 18:09:19 espie Exp $
.\"
.Dd $Mdocdate: February 5 2016 $
.Dt SYSTEM 3
.Os
.Sh NAME
.Nm system
.Nd pass a command to the shell
.Sh SYNOPSIS
.In stdlib.h
.Ft int
.Fn system "const char *string"
.Sh DESCRIPTION
The
.Fn system
function hands the argument
.Fa string
to the command interpreter
.Xr sh 1 .
The calling process waits for the shell to finish executing the command,
ignoring
.Dv SIGINT
and
.Dv SIGQUIT ,
and blocking
.Dv SIGCHLD .
.Pp
If
.Fa string
is
.Dv NULL ,
.Fn system
will return non-zero.
Otherwise,
.Fn system
returns the termination status of the shell in the format specified by
.Xr waitpid 2 .
.Pp
Note that fork handlers established using
.Xr pthread_atfork 3
are not called when a multithreaded program calls
.Fn system .
.Sh RETURN VALUES
If a child process cannot be created, or the termination status of
the shell cannot be obtained,
.Fn system
returns \-1 and sets
.Va errno
to indicate the error.
If execution of the shell fails,
.Fn system
returns the termination status for a program that terminates with a call of
.Fn exit 127 .
.Sh SEE ALSO
.Xr sh 1 ,
.Xr execve 2 ,
.Xr waitpid 2 ,
.Xr popen 3
.Sh STANDARDS
The
.Fn system
function conforms to
.St -ansiC
and
.St -p1003.2-92 .
.Sh HISTORY
The
.Fn system
function first appeared in
.At v6 .
.Sh CAVEATS
Never supply the
.Fn system
function with a command containing any part of an unsanitized user-supplied
string.
Shell meta-characters present will be honored by the
.Xr sh 1
command interpreter.
.Pp
It is often simpler to bypass the shell and run an external command using
.Xr fork 2 ,
.Xr execlp 3 ,
and
.Xr waitpid 2
directly instead of having to sanitize a string for shell consumption.
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