1.\" $NetBSD: getenv.3,v 1.17 2003/08/07 16:43:39 agc 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. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" from: @(#)getenv.3 8.2 (Berkeley) 12/11/93 35.\" 36.Dd April 1, 2003 37.Dt GETENV 3 38.Os 39.Sh NAME 40.Nm getenv , 41.Nm putenv , 42.Nm setenv , 43.Nm unsetenv 44.Nd environment variable functions 45.Sh LIBRARY 46.Lb libc 47.Sh SYNOPSIS 48.In 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 int 56.Fn unsetenv "const char *name" 57.Sh DESCRIPTION 58These functions set, unset and fetch environment variables from the 59host 60.Em environment list . 61For compatibility with differing environment conventions, 62the given arguments 63.Ar name 64and 65.Ar value 66may be appended and prepended, 67respectively, 68with an equal sign 69.Dq Li \&= , 70except for 71.Fn unsetenv . 72.Pp 73The 74.Fn getenv 75function obtains the current value of the environment variable, 76.Ar name . 77If the variable 78.Ar name 79is not in the current environment, 80a null pointer is returned. 81.Pp 82The 83.Fn setenv 84function inserts or resets the environment variable 85.Ar name 86in the current environment list. 87If the variable 88.Ar name 89does not exist in the list, 90it is inserted with the given 91.Ar value . 92If the variable does exist, the argument 93.Ar overwrite 94is tested; if 95.Ar overwrite is 96zero, the 97variable is not reset, otherwise it is reset 98to the given 99.Ar value . 100.Pp 101The 102.Fn putenv 103function takes an argument of the form ``name=value'' and is 104equivalent to: 105.Bd -literal -offset indent 106setenv(name, value, 1); 107.Ed 108.Pp 109The 110.Fn unsetenv 111function 112deletes all instances of the variable name pointed to by 113.Fa name 114from the list. 115.Sh RETURN VALUES 116The functions 117.Fn setenv , 118.Fn putenv 119and 120.Fn unsetenv 121return zero if successful; otherwise the global variable 122.Va errno 123is set to indicate the error and a 124\-1 is returned. 125.Pp 126If 127.Fn getenv 128is successful, the string returned should be considered read-only. 129.Sh ERRORS 130.Bl -tag -width Er 131.It Bq Er EINVAL 132The 133.Fa name 134argument to 135.Fn unsetenv 136is a null pointer, points to an empty string, or points to a string 137containing an 138.Dq Li \&= 139character. 140.It Bq Er ENOMEM 141The function 142.Fn setenv 143or 144.Fn putenv 145failed because they were unable to allocate memory for the environment. 146.El 147.Sh SEE ALSO 148.Xr csh 1 , 149.Xr sh 1 , 150.Xr execve 2 , 151.Xr environ 7 152.Sh STANDARDS 153The 154.Fn getenv 155function conforms to 156.St -ansiC . 157The 158.Fn putenv 159function conforms to 160.St -xpg4 . 161The 162.Fn unsetenv 163function conforms to 164.St -p1003.1-2001 . 165.Sh HISTORY 166The functions 167.Fn setenv 168and 169.Fn unsetenv 170appeared in 171.At v7 . 172The 173.Fn putenv 174function appeared in 175.Bx 4.3 Reno . 176