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.\" @(#)getenv.3 8.2 (Berkeley) 12/11/93 37.\" $FreeBSD: src/lib/libc/stdlib/getenv.3,v 1.4.2.7 2001/12/14 18:33:58 ru Exp $ 38.\" 39.Dd December 11, 1993 40.Dt GETENV 3 41.Os 42.Sh NAME 43.Nm getenv , 44.Nm putenv , 45.Nm setenv , 46.Nm unsetenv 47.Nd environment variable functions 48.Sh LIBRARY 49.Lb libc 50.Sh SYNOPSIS 51.In stdlib.h 52.Ft char * 53.Fn getenv "const char *name" 54.Ft int 55.Fn setenv "const char *name" "const char *value" "int overwrite" 56.Ft int 57.Fn putenv "const char *string" 58.Ft void 59.Fn unsetenv "const char *name" 60.Sh DESCRIPTION 61These functions set, unset and fetch environment variables from the 62host 63.Em environment list . 64For compatibility with differing environment conventions, 65the given arguments 66.Ar name 67and 68.Ar value 69may be appended and prepended, 70respectively, 71with an equal sign 72.Dq Li \&= . 73.Pp 74The 75.Fn getenv 76function obtains the current value of the environment variable, 77.Ar name . 78If the variable 79.Ar name 80is not in the current environment, 81a null pointer is returned. 82.Pp 83The 84.Fn setenv 85function inserts or resets the environment variable 86.Ar name 87in the current environment list. 88If the variable 89.Ar name 90does not exist in the list, 91it is inserted with the given 92.Ar value . 93If the variable does exist, the argument 94.Ar overwrite 95is tested; if 96.Ar overwrite is 97zero, the 98variable is not reset, otherwise it is reset 99to the given 100.Ar value . 101.Pp 102The 103.Fn putenv 104function takes an argument of the form ``name=value'' and is 105equivalent to: 106.Bd -literal -offset indent 107setenv(name, value, 1); 108.Ed 109.Pp 110The 111.Fn unsetenv 112function 113deletes all instances of the variable name pointed to by 114.Fa name 115from the list. 116.Sh RETURN VALUES 117.Rv -std setenv putenv 118.Sh ERRORS 119.Bl -tag -width Er 120.It Bq Er ENOMEM 121The function 122.Fn setenv 123or 124.Fn putenv 125failed because they were unable to allocate memory for the environment. 126.El 127.Sh SEE ALSO 128.Xr csh 1 , 129.Xr sh 1 , 130.Xr execve 2 , 131.Xr environ 7 132.Sh STANDARDS 133The 134.Fn getenv 135function conforms to 136.St -isoC . 137.Sh BUGS 138Successive calls to 139.Fn setenv 140or 141.Fn putenv 142assigning a differently sized 143.Ar value 144to the same 145.Ar name 146will result in a memory leak. The 147.Fx 148semantics for these functions 149(namely, that the contents of 150.Ar value 151are copied and that old values remain accessible indefinitely) make this 152bug unavoidable. Future versions may eliminate one or both of these 153semantic guarantees in order to fix the bug. 154.Sh HISTORY 155The functions 156.Fn setenv 157and 158.Fn unsetenv 159appeared in 160.At v7 . 161The 162.Fn putenv 163function appeared in 164.Bx 4.3 Reno . 165