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. All advertising materials mentioning features or use of this software 17.\" must display the following acknowledgement: 18.\" This product includes software developed by the University of 19.\" California, Berkeley and its contributors. 20.\" 4. Neither the name of the University nor the names of its contributors 21.\" may be used to endorse or promote products derived from this software 22.\" without specific prior written permission. 23.\" 24.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34.\" SUCH DAMAGE. 35.\" 36.\" $OpenBSD: getenv.3,v 1.7 2000/04/20 13:50:02 aaron Exp $ 37.\" 38.Dd December 11, 1993 39.Dt GETENV 3 40.Os 41.Sh NAME 42.Nm getenv , 43.Nm putenv , 44.Nm setenv , 45.Nm unsetenv 46.Nd environment variable functions 47.Sh SYNOPSIS 48.Fd #include <stdlib.h> 49.Ft char * 50.Fn getenv "const char *name" 51.Ft int 52.Fn setenv "const char *name" "const char *value" "int overwrite" 53.Ft int 54.Fn putenv "const char *string" 55.Ft void 56.Fn unsetenv "const char *name" 57.Sh DESCRIPTION 58These functions set, unset, and fetch environment variables from the host 59.Em environment list . 60For compatibility with differing environment conventions, the given arguments 61.Fa name 62and 63.Fa value 64may be appended and prepended, respectively, with an equal sign 65.Dq Li \&= . 66.Pp 67The 68.Fn getenv 69function obtains the current value of the environment variable, 70.Fa name . 71If the variable 72.Fa name 73is not in the current environment, a null pointer is returned. 74.Pp 75The 76.Fn setenv 77function inserts or resets the environment variable 78.Fa name 79in the current environment list. 80If the variable 81.Fa name 82does not exist in the list, it is inserted with the given 83.Fa value . 84If the variable does exist, the argument 85.Fa overwrite 86is tested; if 87.Fa overwrite 88is zero, the variable is not reset, otherwise it is reset to the given 89.Fa value . 90.Pp 91The 92.Fn putenv 93function takes an argument of the form 94.Ar name Ns No = Ns Ar value 95and is equivalent to: 96.Bd -literal -offset indent 97setenv(name, value, 1); 98.Ed 99.Pp 100The 101.Fn unsetenv 102function deletes all instances of the variable name pointed to by 103.Fa name 104from the list. 105.Sh RETURN VALUES 106The functions 107.Fn setenv 108and 109.Fn putenv 110return zero if successful; otherwise the global variable 111.Va errno 112is set to indicate the error and \-1 is returned. 113.Pp 114If 115.Fn getenv 116is successful, the string returned should be considered read-only. 117.Sh ERRORS 118.Bl -tag -width [ENOMEM] 119.It Bq Er ENOMEM 120The function 121.Fn setenv 122or 123.Fn putenv 124failed because they were unable to allocate memory for the environment. 125.El 126.Sh SEE ALSO 127.Xr csh 1 , 128.Xr sh 1 , 129.Xr execve 2 , 130.Xr environ 7 131.Sh STANDARDS 132The 133.Fn getenv 134function conforms to 135.St -ansiC . 136.Sh HISTORY 137The functions 138.Fn setenv 139and 140.Fn unsetenv 141appeared in 142.At v7 . 143The 144.Fn putenv 145function appeared in 146.Bx 4.3 Reno . 147