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