[unix-history] / lib / libc / stdlib / getenv.3

.\" Copyright (c) 1988, 1991 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	6.11 (Berkeley) 6/29/91
.\"
.Dd June 29, 1991
.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
performs the equivalent of:
.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 .
Commit	Line	Data
15637ed4 RG	1	.\" Copyright (c) 1988, 1991 The Regents of the University of California.
	2	.\" 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 6.11 (Berkeley) 6/29/91
	37	.\"
	38	.Dd June 29, 1991
	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
	58	These functions set, unset and fetch environment variables from the
	59	host
	60	.Em environment list .
	61	For compatibility with differing environment conventions,
	62	the given arguments
	63	.Ar name
	64	and
65	.Ar value
66	may be appended and prepended,
67	respectively,
68	with an equal sign
69	.Dq Li \&= .
70	.Pp
71	The
72	.Fn getenv
73	function obtains the current value of the environment variable,
74	.Ar name .
75	If the variable
76	.Ar name
77	is not in the current environment ,
78	a null pointer is returned.
79	.Pp
80	The
81	.Fn setenv
82	function inserts or resets the environment variable
83	.Ar name
84	in the current environment list.
85	If the variable
86	.Ar name
87	does not exist in the list,
88	it is inserted with the given
89	.Ar value.
90	If the variable does exist, the argument
91	.Ar overwrite
92	is tested; if
93	.Ar overwrite is
94	zero, the
95	variable is not reset, otherwise it is reset
96	to the given
97	.Ar value .
98	.Pp
99	The
100	.Fn putenv
101	function
102	performs the equivalent of:
103	.Bd -literal -offset indent
104	setenv(name, value, 1);
105	.Ed
106	.Pp
107	The
108	.Fn unsetenv
109	function
110	deletes all instances of the variable name pointed to by
111	.Fa name
112	from the list.
113	.Sh RETURN VALUES
114	The functions
115	.Fn setenv
116	and
117	.Fn putenv
118	return zero if successful; otherwise the global variable
119	.Va errno
120	is set to indicate the error and a
121	\-1 is returned.
122	.Sh ERRORS
123	.Bl -tag -width [ENOMEM]
124	.It Bq Er ENOMEM
125	The function
126	.Fn setenv
127	or
128	.Fn putenv
129	failed 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
137	The
138	.Fn getenv
139	function conforms to
140	.St -ansiC .
141	.Sh HISTORY
142	The functions
143	.Fn setenv
144	and
145	.Fn unsetenv
146	appeared in
147	.At v7 .
148	The
149	.Fn putenv
150	function appeared in
151	.Bx 4.3 Reno .