1.\" Copyright (c) 1988, 1991, 1993 2.\" The Regents of the University of California. 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: getenv.3,v 1.21 2014/07/11 09:24:03 tedu Exp $ 33.\" 34.Dd $Mdocdate: July 11 2014 $ 35.Dt GETENV 3 36.Os 37.Sh NAME 38.Nm getenv , 39.Nm putenv , 40.Nm setenv , 41.Nm unsetenv 42.Nd environment variable functions 43.Sh SYNOPSIS 44.In stdlib.h 45.Ft char * 46.Fn getenv "const char *name" 47.Ft int 48.Fn setenv "const char *name" "const char *value" "int overwrite" 49.Ft int 50.Fn putenv "char *string" 51.Ft int 52.Fn unsetenv "const char *name" 53.Sh DESCRIPTION 54These functions set, unset, and fetch environment variables from the host 55.Em environment list . 56.Pp 57The 58.Fn getenv 59function obtains the current value of the environment variable 60.Fa name . 61If the variable 62.Fa name 63is not in the current environment, a null pointer is returned. 64.Pp 65The 66.Fn setenv 67function inserts or resets the environment variable 68.Fa name 69in the current environment list. 70If the variable 71.Fa name 72does not exist in the list, it is inserted with the given 73.Fa value . 74If the variable does exist, the argument 75.Fa overwrite 76is tested; if 77.Fa overwrite 78is zero, the variable is not reset, otherwise it is reset to the given 79.Fa value . 80.Pp 81The 82.Fn putenv 83function takes an argument of the form 84.Ar name Ns = Ns Ar value . 85The memory pointed to by 86.Ar string 87becomes part of the environment and must not be deallocated by the caller. 88If the variable already exists, it will be overwritten. 89A common source of bugs is to pass a 90.Ar string 91argument that is a locally scoped string buffer. 92This will result in corruption of the environment after leaving 93the scope in which the variable is defined. 94For this reason, the 95.Fn setenv 96function is preferred over 97.Fn putenv . 98.Pp 99The 100.Fn unsetenv 101function deletes all instances of the variable name pointed to by 102.Fa name 103from the list. 104.Sh RETURN VALUES 105.Rv -std putenv setenv unsetenv 106.Pp 107The 108.Fn getenv 109function returns a pointer to the requested value, or 110.Dv NULL 111if it could not be found. 112If 113.Fn getenv 114is successful, the string returned should be considered read-only. 115.Sh ERRORS 116.Bl -tag -width Er 117.It Bq Er EINVAL 118The 119.Fn setenv 120or 121.Fn unsetenv 122function was passed an empty 123.Ar name 124or a NULL pointer, or was passed a 125.Ar name 126containing an 127.Sq = 128character. 129.Pp 130The 131.Fn putenv 132function was passed a 133.Ar string 134that did not contain an 135.Sq = 136character. 137.It Bq Er ENOMEM 138The 139.Fn setenv 140or 141.Fn putenv 142function failed because it was unable to allocate memory for the environment. 143.El 144.Sh SEE ALSO 145.Xr csh 1 , 146.Xr sh 1 , 147.Xr execve 2 , 148.Xr issetugid 2 , 149.Xr environ 7 150.Sh STANDARDS 151The 152.Fn getenv 153function conforms to 154.St -ansiC . 155The 156.Fn putenv , 157.Fn setenv , 158and 159.Fn unsetenv 160functions conform to 161.St -p1003.1-2008 . 162.Sh HISTORY 163The function 164.Fn getenv 165appeared in 166.At v7 167and 168.Bx 3 . 169The functions 170.Fn setenv 171and 172.Fn unsetenv 173appeared in 174.Bx 4.3 Tahoe . 175The 176.Fn putenv 177function appeared in 178.Bx 4.3 Reno . 179.Sh CAVEATS 180Library code must be careful about using 181.Fn getenv 182to read untrusted environment variables in setuid programs. 183The 184.Fn issetugid 185function is provided for this purpose. 186