1.\" Copyright (c) 1990, 1991 The Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" the American National Standards Committee X3, on Information 6.\" Processing Systems. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" $OpenBSD: system.3,v 1.14 2016/02/05 18:09:19 espie Exp $ 33.\" 34.Dd $Mdocdate: February 5 2016 $ 35.Dt SYSTEM 3 36.Os 37.Sh NAME 38.Nm system 39.Nd pass a command to the shell 40.Sh SYNOPSIS 41.In stdlib.h 42.Ft int 43.Fn system "const char *string" 44.Sh DESCRIPTION 45The 46.Fn system 47function hands the argument 48.Fa string 49to the command interpreter 50.Xr sh 1 . 51The calling process waits for the shell to finish executing the command, 52ignoring 53.Dv SIGINT 54and 55.Dv SIGQUIT , 56and blocking 57.Dv SIGCHLD . 58.Pp 59If 60.Fa string 61is 62.Dv NULL , 63.Fn system 64will return non-zero. 65Otherwise, 66.Fn system 67returns the termination status of the shell in the format specified by 68.Xr waitpid 2 . 69.Pp 70Note that fork handlers established using 71.Xr pthread_atfork 3 72are not called when a multithreaded program calls 73.Fn system . 74.Sh RETURN VALUES 75If a child process cannot be created, or the termination status of 76the shell cannot be obtained, 77.Fn system 78returns \-1 and sets 79.Va errno 80to indicate the error. 81If execution of the shell fails, 82.Fn system 83returns the termination status for a program that terminates with a call of 84.Fn exit 127 . 85.Sh SEE ALSO 86.Xr sh 1 , 87.Xr execve 2 , 88.Xr waitpid 2 , 89.Xr popen 3 90.Sh STANDARDS 91The 92.Fn system 93function conforms to 94.St -ansiC 95and 96.St -p1003.2-92 . 97.Sh HISTORY 98The 99.Fn system 100function first appeared in 101.At v6 . 102.Sh CAVEATS 103Never supply the 104.Fn system 105function with a command containing any part of an unsanitized user-supplied 106string. 107Shell meta-characters present will be honored by the 108.Xr sh 1 109command interpreter. 110.Pp 111It is often simpler to bypass the shell and run an external command using 112.Xr fork 2 , 113.Xr execlp 3 , 114and 115.Xr waitpid 2 116directly instead of having to sanitize a string for shell consumption. 117