1.\" $NetBSD: getenv.3,v 1.16 2003/04/16 13:34:46 wiz Exp $ 2.\" 3.\" Copyright (c) 1988, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" This code is derived from software contributed to Berkeley by 7.\" the American National Standards Committee X3, on Information 8.\" Processing Systems. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 3. All advertising materials mentioning features or use of this software 19.\" must display the following acknowledgement: 20.\" This product includes software developed by the University of 21.\" California, Berkeley and its contributors. 22.\" 4. Neither the name of the University nor the names of its contributors 23.\" may be used to endorse or promote products derived from this software 24.\" without specific prior written permission. 25.\" 26.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36.\" SUCH DAMAGE. 37.\" 38.\" from: @(#)getenv.3 8.2 (Berkeley) 12/11/93 39.\" 40.Dd April 1, 2003 41.Dt GETENV 3 42.Os 43.Sh NAME 44.Nm getenv , 45.Nm putenv , 46.Nm setenv , 47.Nm unsetenv 48.Nd environment variable functions 49.Sh LIBRARY 50.Lb libc 51.Sh SYNOPSIS 52.In stdlib.h 53.Ft char * 54.Fn getenv "const char *name" 55.Ft int 56.Fn setenv "const char *name" "const char *value" "int overwrite" 57.Ft int 58.Fn putenv "const char *string" 59.Ft int 60.Fn unsetenv "const char *name" 61.Sh DESCRIPTION 62These functions set, unset and fetch environment variables from the 63host 64.Em environment list . 65For compatibility with differing environment conventions, 66the given arguments 67.Ar name 68and 69.Ar value 70may be appended and prepended, 71respectively, 72with an equal sign 73.Dq Li \&= , 74except for 75.Fn unsetenv . 76.Pp 77The 78.Fn getenv 79function obtains the current value of the environment variable, 80.Ar name . 81If the variable 82.Ar name 83is not in the current environment, 84a null pointer is returned. 85.Pp 86The 87.Fn setenv 88function inserts or resets the environment variable 89.Ar name 90in the current environment list. 91If the variable 92.Ar name 93does not exist in the list, 94it is inserted with the given 95.Ar value . 96If the variable does exist, the argument 97.Ar overwrite 98is tested; if 99.Ar overwrite is 100zero, the 101variable is not reset, otherwise it is reset 102to the given 103.Ar value . 104.Pp 105The 106.Fn putenv 107function takes an argument of the form ``name=value'' and is 108equivalent to: 109.Bd -literal -offset indent 110setenv(name, value, 1); 111.Ed 112.Pp 113The 114.Fn unsetenv 115function 116deletes all instances of the variable name pointed to by 117.Fa name 118from the list. 119.Sh RETURN VALUES 120The functions 121.Fn setenv , 122.Fn putenv 123and 124.Fn unsetenv 125return zero if successful; otherwise the global variable 126.Va errno 127is set to indicate the error and a 128\-1 is returned. 129.Pp 130If 131.Fn getenv 132is successful, the string returned should be considered read-only. 133.Sh ERRORS 134.Bl -tag -width Er 135.It Bq Er EINVAL 136The 137.Fa name 138argument to 139.Fn unsetenv 140is a null pointer, points to an empty string, or points to a string 141containing an 142.Dq Li \&= 143character. 144.It Bq Er ENOMEM 145The function 146.Fn setenv 147or 148.Fn putenv 149failed because they were unable to allocate memory for the environment. 150.El 151.Sh SEE ALSO 152.Xr csh 1 , 153.Xr sh 1 , 154.Xr execve 2 , 155.Xr environ 7 156.Sh STANDARDS 157The 158.Fn getenv 159function conforms to 160.St -ansiC . 161The 162.Fn putenv 163function conforms to 164.St -xpg4 . 165The 166.Fn unsetenv 167function conforms to 168.St -p1003.1-2001 . 169.Sh HISTORY 170The functions 171.Fn setenv 172and 173.Fn unsetenv 174appeared in 175.At v7 . 176The 177.Fn putenv 178function appeared in 179.Bx 4.3 Reno . 180