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.\"	@(#)getenv.3	6.9 (Berkeley) 5/17/90
.\"
.TH GETENV 3 "May 17, 1990"
.AT 3
.SH NAME
getenv, putenv, setenv, unsetenv \- manipulate environmental variables
.SH SYNOPSIS
.nf
.ft B
#include <stdlib.h>

char *
getenv(const char *name);

setenv(const char *name, const char *value, int overwrite);

putenv(const char *string);

void
unsetenv(const char *name);
.ft R
.fi
.SH DESCRIPTION
.I Getenv
searches the environment list (see
.IR environ (7))
for a string of the form \fIname\fP\fB=\fP\fIvalue\fP and returns
a pointer to the string
.I value
if such a string is present, and a NULL pointer if it is not.
.PP
.I Setenv
searches the environment list as
.I getenv
does; if the string
.I name
is not found, a string of the form \fIname\fP\fB=\fP\fIvalue\fP is
added to the environment.
If it is found, and
.I overwrite
is non-zero, its value is changed to
.IR value .
.I Setenv
returns 0 on success and -1 on failure, setting the external variable
.IR errno .
.PP
.I Putenv
takes an argument of the form ``\fIname\fR=\fIvalue\fR'' and is the
equivalent of:
.sp
.RS
setenv(name, value, 1);
.RE
.PP
.I Unsetenv
removes all occurrences of the string
.I name
from the environment.
There is no library provision for completely removing the current
environment.
It is suggested that the following code be used to do so.
.sp
.RS
.nf
static char	*envinit[1];
extern char	**environ;
environ = envinit;
.fi
.RE
.PP
All of these routines permit, but do not require, a trailing equals
(``='') sign on
.I name
or a leading equals sign on
.IR value .
.SH ERRORS
.TP
[ENOMEM]
.I Setenv
or
.I putenv
failed because they were unable to allocate memory for the environment.
.SH SEE ALSO
csh(1), sh(1), execve(2), environ(7)
.SH STANDARDS
.B Getenv
conforms to ANSI X3.159-1989 (``ANSI C'').

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