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.\" 38.Dd December 11, 1993 39.Dt GETENV 3 40.Os 41.Sh NAME 42.Nm getenv , 43.Nm putenv , 44.Nm setenv , 45.Nm unsetenv 46.Nd environment variable functions 47.Sh SYNOPSIS 48.Fd #include <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 void 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 \&= . 70.Pp 71The 72.Fn getenv 73function obtains the current value of the environment variable, 74.Ar name . 75If the variable 76.Ar name 77is not in the current environment, 78a null pointer is returned. 79.Pp 80The 81.Fn setenv 82function inserts or resets the environment variable 83.Ar name 84in the current environment list. 85If the variable 86.Ar name 87does not exist in the list, 88it is inserted with the given 89.Ar value. 90If the variable does exist, the argument 91.Ar overwrite 92is tested; if 93.Ar overwrite is 94zero, the 95variable is not reset, otherwise it is reset 96to the given 97.Ar 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 functions 115.Fn setenv 116and 117.Fn putenv 118return zero if successful; otherwise the global variable 119.Va errno 120is set to indicate the error and a 121\-1 is returned. 122.Sh ERRORS 123.Bl -tag -width [ENOMEM] 124.It Bq Er ENOMEM 125The function 126.Fn setenv 127or 128.Fn putenv 129failed because they were unable to allocate memory for the environment. 130.El 131.Sh SEE ALSO 132.Xr csh 1 , 133.Xr sh 1 , 134.Xr execve 2 , 135.Xr environ 7 136.Sh STANDARDS 137The 138.Fn getenv 139function conforms to 140.St -ansiC . 141.Sh HISTORY 142The functions 143.Fn setenv 144and 145.Fn unsetenv 146appeared in 147.At v7 . 148The 149.Fn putenv 150function appeared in 151.Bx 4.3 Reno . 152