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 1.13 2009/06/03 15:52:16 millert Exp $ 33.\" 34.Dd $Mdocdate: June 3 2009 $ 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.Fd #include <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 . 56For compatibility with differing environment conventions, the given arguments 57.Fa name 58and 59.Fa value 60may be appended and prepended, respectively, with an equal sign 61.Dq Li \&= . 62.Pp 63The 64.Fn getenv 65function obtains the current value of the environment variable 66.Fa name . 67If the variable 68.Fa name 69is not in the current environment, a null pointer is returned. 70.Pp 71The 72.Fn setenv 73function inserts or resets the environment variable 74.Fa name 75in the current environment list. 76If the variable 77.Fa name 78does not exist in the list, it is inserted with the given 79.Fa value . 80If the variable does exist, the argument 81.Fa overwrite 82is tested; if 83.Fa overwrite 84is zero, the variable is not reset, otherwise it is reset to the given 85.Fa value . 86.Pp 87The 88.Fn putenv 89function takes an argument of the form 90.Ar name Ns = Ns Ar value . 91The memory pointed to by 92.Ar string 93becomes part of the environment and must not be deallocated by the caller. 94If the variable already exists, it will be overwritten. 95A common source of bugs is to pass a 96.Ar string 97argument that is a locally scoped string buffer. 98This will result in corruption of the environment after leaving 99the scope in which the variable is defined. 100For this reason, the 101.Fn setenv 102function is preferred over 103.Fn putenv . 104.Pp 105The 106.Fn unsetenv 107function deletes all instances of the variable name pointed to by 108.Fa name 109from the list. 110.Sh RETURN VALUES 111These functions 112return zero if successful; otherwise the global variable 113.Va errno 114is set to indicate the error and \-1 is returned. 115.Pp 116If 117.Fn getenv 118is successful, the string returned should be considered read-only. 119.Sh ERRORS 120.Bl -tag -width Er 121.It Bq Er EINVAL 122The 123.Fn setenv 124or 125.Fn putenv 126function was passed a 127.Ar name 128containing an 129.Sq = 130character. 131.Pp 132The 133.Fn putenv 134function was passed a 135.Ar string 136that did not contain an 137.Sq = 138character. 139.It Bq Er ENOMEM 140The 141.Fn setenv 142or 143.Fn putenv 144function failed because it was unable to allocate memory for the environment. 145.El 146.Sh SEE ALSO 147.Xr csh 1 , 148.Xr sh 1 , 149.Xr execve 2 , 150.Xr environ 7 151.Sh STANDARDS 152The 153.Fn getenv 154function conforms to 155.St -ansiC . 156.Sh HISTORY 157The function 158.Fn getenv 159appeared in 160.At v7 161and 162.Bx 3 . 163The functions 164.Fn setenv 165and 166.Fn unsetenv 167appeared in 168.Bx 4.3 Tahoe . 169The 170.Fn putenv 171function appeared in 172.Bx 4.3 Reno . 173