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.\" $FreeBSD$ 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.Fa name 67and 68.Fa 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.Fa name . 78.Pp 79The 80.Fn setenv 81function inserts or resets the environment variable 82.Fa name 83in the current environment list. 84If the variable 85.Fa name 86does not exist in the list, 87it is inserted with the given 88.Fa value . 89If the variable does exist, the argument 90.Fa overwrite 91is tested; if 92.Fa overwrite 93is 94zero, the 95variable is not reset, otherwise it is reset 96to the given 97.Fa value . 98.Pp 99The 100.Fn putenv 101function takes an argument of the form ``name=value'' and is 102equivalent to: 103.Bd -literal -offset indent 104setenv(name, value, 1); 105.Ed 106.Pp 107The 108.Fn unsetenv 109function 110deletes all instances of the variable name pointed to by 111.Fa name 112from the list. 113.Sh RETURN VALUES 114The 115.Fn getenv 116function returns the value of the environment variable as a 117.Dv NUL Ns 118-terminated string. 119If the variable 120.Fa name 121is not in the current environment, 122.Dv NULL 123is returned. 124.Pp 125.Rv -std setenv putenv 126.Sh ERRORS 127.Bl -tag -width Er 128.It Bq Er ENOMEM 129The function 130.Fn setenv 131or 132.Fn putenv 133failed because they were unable to allocate memory for the environment. 134.El 135.Sh SEE ALSO 136.Xr csh 1 , 137.Xr sh 1 , 138.Xr execve 2 , 139.Xr environ 7 140.Sh STANDARDS 141The 142.Fn getenv 143function conforms to 144.St -isoC . 145.Sh BUGS 146Successive calls to 147.Fn setenv 148or 149.Fn putenv 150assigning a differently sized 151.Fa value 152to the same 153.Fa name 154will result in a memory leak. 155The 156.Fx 157semantics for these functions 158(namely, that the contents of 159.Fa value 160are copied and that old values remain accessible indefinitely) make this 161bug unavoidable. 162Future versions may eliminate one or both of these 163semantic guarantees in order to fix the bug. 164.Sh HISTORY 165The functions 166.Fn setenv 167and 168.Fn unsetenv 169appeared in 170.At v7 . 171The 172.Fn putenv 173function appeared in 174.Bx 4.3 Reno . 175