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+.\" Copyright (c) 1988, 1991, 1993
+.\"	The Regents of the University of California.  All rights reserved.
+.\"
+.\" This code is derived from software contributed to Berkeley by
+.\" the American National Standards Committee X3, on Information
+.\" Processing Systems.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"	This product includes software developed by the University of
+.\"	California, Berkeley and its contributors.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"     @(#)getenv.3	8.2 (Berkeley) 12/11/93
+.\"
+.Dd December 11, 1993
+.Dt GETENV 3
+.Os
+.Sh NAME
+.Nm getenv ,
+.Nm putenv ,
+.Nm setenv ,
+.Nm unsetenv
+.Nd environment variable functions
+.Sh SYNOPSIS
+.Fd #include <stdlib.h>
+.Ft char *
+.Fn getenv "const char *name"
+.Ft int
+.Fn setenv "const char *name" "const char *value" "int overwrite"
+.Ft int
+.Fn putenv "const char *string"
+.Ft void
+.Fn unsetenv "const char *name"
+.Sh DESCRIPTION
+These functions set, unset and fetch environment variables from the
+host
+.Em environment list .
+For compatibility with differing environment conventions,
+the given arguments
+.Ar name
+and
+.Ar value
+may be appended and prepended, 
+respectively,
+with an equal sign
+.Dq Li \&= .
+.Pp
+The
+.Fn getenv
+function obtains the current value of the environment variable,
+.Ar name .
+If the variable
+.Ar name
+is not in the current environment,
+a null pointer is returned.
+.Pp
+The
+.Fn setenv
+function inserts or resets the environment variable
+.Ar name
+in the current environment list.
+If the variable
+.Ar name
+does not exist in the list,
+it is inserted with the given
+.Ar value.
+If the variable does exist, the argument
+.Ar overwrite
+is tested; if
+.Ar overwrite is
+zero, the
+variable is not reset, otherwise it is reset
+to the given
+.Ar value .
+.Pp
+The
+.Fn putenv
+function takes an argument of the form ``name=value'' and is
+equivalent to:
+.Bd -literal -offset indent
+setenv(name, value, 1);
+.Ed
+.Pp
+The
+.Fn unsetenv
+function
+deletes all instances of the variable name pointed to by
+.Fa name
+from the list.
+.Sh RETURN VALUES
+The functions
+.Fn setenv
+and
+.Fn putenv
+return zero if successful; otherwise the global variable
+.Va errno
+is set to indicate the error and a
+\-1 is returned.
+.Sh ERRORS
+.Bl -tag -width [ENOMEM]
+.It Bq Er ENOMEM
+The function
+.Fn setenv
+or
+.Fn putenv
+failed because they were unable to allocate memory for the environment.
+.El
+.Sh SEE ALSO
+.Xr csh 1 ,
+.Xr sh 1 ,
+.Xr execve 2 ,
+.Xr environ 7
+.Sh STANDARDS
+The
+.Fn getenv
+function conforms to
+.St -ansiC .
+.Sh HISTORY
+The functions
+.Fn setenv
+and
+.Fn unsetenv
+appeared in
+.At v7 .
+The
+.Fn putenv
+function appeared in
+.Bx 4.3 Reno .