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 1.12 2007/05/31 19:19:31 jmc Exp $ 33.\" 34.Dd $Mdocdate: May 31 2007 $ 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 "const char *string" 51.Ft void 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 91and is equivalent to: 92.Bd -literal -offset indent 93setenv(name, value, 1); 94.Ed 95.Pp 96The 97.Fn unsetenv 98function deletes all instances of the variable name pointed to by 99.Fa name 100from the list. 101.Sh RETURN VALUES 102The functions 103.Fn setenv 104and 105.Fn putenv 106return zero if successful; otherwise the global variable 107.Va errno 108is set to indicate the error and \-1 is returned. 109.Pp 110If 111.Fn getenv 112is successful, the string returned should be considered read-only. 113.Sh ERRORS 114.Bl -tag -width Er 115.It Bq Er ENOMEM 116The function 117.Fn setenv 118or 119.Fn putenv 120failed because they were unable to allocate memory for the environment. 121.El 122.Sh SEE ALSO 123.Xr csh 1 , 124.Xr sh 1 , 125.Xr execve 2 , 126.Xr environ 7 127.Sh STANDARDS 128The 129.Fn getenv 130function conforms to 131.St -ansiC . 132.Sh HISTORY 133The function 134.Fn getenv 135appeared in 136.At v7 137and 138.Bx 3 . 139The functions 140.Fn setenv 141and 142.Fn unsetenv 143appeared in 144.Bx 4.3 Tahoe . 145The 146.Fn putenv 147function appeared in 148.Bx 4.3 Reno . 149