1.\" $NetBSD: getenv.3,v 1.13 2002/08/10 17:14:50 yamt 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 August 11, 2002 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.Fd #include \*[Lt]stdlib.h\*[Gt] 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 void 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 \&= . 74.Pp 75The 76.Fn getenv 77function obtains the current value of the environment variable, 78.Ar name . 79If the variable 80.Ar name 81is not in the current environment, 82a null pointer is returned. 83.Pp 84The 85.Fn setenv 86function inserts or resets the environment variable 87.Ar name 88in the current environment list. 89If the variable 90.Ar name 91does not exist in the list, 92it is inserted with the given 93.Ar value . 94If the variable does exist, the argument 95.Ar overwrite 96is tested; if 97.Ar overwrite is 98zero, the 99variable is not reset, otherwise it is reset 100to the given 101.Ar 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 118The functions 119.Fn setenv 120and 121.Fn putenv 122return zero if successful; otherwise the global variable 123.Va errno 124is set to indicate the error and a 125\-1 is returned. 126.Pp 127If 128.Fn getenv 129is successful, the string returned should be considered read-only. 130.Sh ERRORS 131.Bl -tag -width Er 132.It Bq Er ENOMEM 133The function 134.Fn setenv 135or 136.Fn putenv 137failed because they were unable to allocate memory for the environment. 138.El 139.Sh SEE ALSO 140.Xr csh 1 , 141.Xr sh 1 , 142.Xr execve 2 , 143.Xr environ 7 144.Sh STANDARDS 145The 146.Fn getenv 147function conforms to 148.St -ansiC . 149The 150.Fn putenv 151function conforms to 152.St -xpg4 . 153.Sh HISTORY 154The functions 155.Fn setenv 156and 157.Fn unsetenv 158appeared in 159.At v7 . 160The 161.Fn putenv 162function appeared in 163.Bx 4.3 Reno . 164