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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. | |
dc71b7ab | 16 | .\" 3. Neither the name of the University nor the names of its contributors |
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17 | .\" may be used to endorse or promote products derived from this software |
18 | .\" without specific prior written permission. | |
19 | .\" | |
20 | .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND | |
21 | .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |
22 | .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |
23 | .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE | |
24 | .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |
25 | .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | |
26 | .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |
27 | .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |
28 | .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | |
29 | .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |
30 | .\" SUCH DAMAGE. | |
31 | .\" | |
32 | .\" @(#)getenv.3 8.2 (Berkeley) 12/11/93 | |
a0ba0189 | 33 | .\" $FreeBSD: head/lib/libc/stdlib/getenv.3 251069 2013-05-28 20:57:40Z emaste $ |
984263bc | 34 | .\" |
a0ba0189 | 35 | .Dd September 9, 2015 |
984263bc MD |
36 | .Dt GETENV 3 |
37 | .Os | |
38 | .Sh NAME | |
39 | .Nm getenv , | |
40 | .Nm putenv , | |
41 | .Nm setenv , | |
42 | .Nm unsetenv | |
43 | .Nd environment variable functions | |
44 | .Sh LIBRARY | |
45 | .Lb libc | |
46 | .Sh SYNOPSIS | |
47 | .In stdlib.h | |
48 | .Ft char * | |
49 | .Fn getenv "const char *name" | |
50 | .Ft int | |
51 | .Fn setenv "const char *name" "const char *value" "int overwrite" | |
52 | .Ft int | |
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53 | .Fn putenv "char *string" |
54 | .Ft int | |
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55 | .Fn unsetenv "const char *name" |
56 | .Sh DESCRIPTION | |
57 | These functions set, unset and fetch environment variables from the | |
58 | host | |
59 | .Em environment list . | |
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60 | .Pp |
61 | The | |
62 | .Fn getenv | |
63 | function obtains the current value of the environment variable, | |
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64 | .Fa name . |
65 | The application should not modify the string pointed | |
66 | to by the | |
67 | .Fn getenv | |
68 | function. | |
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69 | .Pp |
70 | The | |
71 | .Fn setenv | |
72 | function inserts or resets the environment variable | |
5d0641a4 | 73 | .Fa name |
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74 | in the current environment list. |
75 | If the variable | |
5d0641a4 | 76 | .Fa name |
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77 | does not exist in the list, |
78 | it is inserted with the given | |
5d0641a4 | 79 | .Fa value . |
984263bc | 80 | If the variable does exist, the argument |
5d0641a4 | 81 | .Fa overwrite |
984263bc | 82 | is tested; if |
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83 | .Fa overwrite |
84 | is zero, the | |
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85 | variable is not reset, otherwise it is reset |
86 | to the given | |
5d0641a4 | 87 | .Fa value . |
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88 | .Pp |
89 | The | |
90 | .Fn putenv | |
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91 | function takes an argument of the form ``name=value'' and |
92 | puts it directly into the current environment, | |
93 | so altering the argument shall change the environment. | |
94 | If the variable | |
95 | .Fa name | |
96 | does not exist in the list, | |
97 | it is inserted with the given | |
98 | .Fa value . | |
99 | If the variable | |
100 | .Fa name | |
101 | does exist, it is reset to the given | |
102 | .Fa value . | |
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103 | .Pp |
104 | The | |
105 | .Fn unsetenv | |
106 | function | |
107 | deletes all instances of the variable name pointed to by | |
108 | .Fa name | |
109 | from the list. | |
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110 | .Pp |
111 | If corruption (e.g., a name without a value) is detected while making a copy of | |
112 | environ for internal usage, then | |
113 | .Fn setenv , | |
114 | .Fn unsetenv | |
115 | and | |
116 | .Fn putenv | |
117 | will output a warning to stderr about the issue, drop the corrupt entry and | |
118 | complete the task without error. | |
984263bc | 119 | .Sh RETURN VALUES |
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120 | The |
121 | .Fn getenv | |
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122 | function returns the value of the environment variable as a |
123 | .Dv NUL Ns | |
124 | -terminated string. | |
125 | If the variable | |
126 | .Fa name | |
127 | is not in the current environment, | |
128 | .Dv NULL | |
129 | is returned. | |
130 | .Pp | |
131 | .Rv -std setenv putenv unsetenv | |
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132 | .Sh ERRORS |
133 | .Bl -tag -width Er | |
5d0641a4 | 134 | .It Bq Er EINVAL |
984263bc | 135 | The function |
5d0641a4 | 136 | .Fn getenv , |
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137 | .Fn setenv |
138 | or | |
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139 | .Fn unsetenv |
140 | failed because the | |
141 | .Fa name | |
142 | is a | |
143 | .Dv NULL | |
144 | pointer, points to an empty string, or points to a string containing an | |
145 | .Dq Li \&= | |
146 | character. | |
147 | .Pp | |
148 | The function | |
149 | .Fn putenv | |
150 | failed because | |
151 | .Fa string | |
152 | is a | |
153 | .Dv NULL | |
154 | pointer, | |
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155 | .Fa string |
156 | is without an | |
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157 | .Dq Li \&= |
158 | character or | |
159 | .Dq Li \&= | |
160 | is the first character in | |
161 | .Fa string . | |
162 | This does not follow the | |
163 | .Tn POSIX | |
164 | specification. | |
165 | .It Bq Er ENOMEM | |
166 | The function | |
167 | .Fn setenv , | |
168 | .Fn unsetenv | |
169 | or | |
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170 | .Fn putenv |
171 | failed because they were unable to allocate memory for the environment. | |
172 | .El | |
173 | .Sh SEE ALSO | |
174 | .Xr csh 1 , | |
175 | .Xr sh 1 , | |
176 | .Xr execve 2 , | |
177 | .Xr environ 7 | |
178 | .Sh STANDARDS | |
179 | The | |
180 | .Fn getenv | |
181 | function conforms to | |
182 | .St -isoC . | |
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183 | The |
184 | .Fn setenv , | |
185 | .Fn putenv | |
186 | and | |
187 | .Fn unsetenv | |
188 | functions conforms to | |
189 | .St -p1003.1-2001 . | |
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190 | .Sh HISTORY |
191 | The functions | |
192 | .Fn setenv | |
193 | and | |
194 | .Fn unsetenv | |
195 | appeared in | |
196 | .At v7 . | |
197 | The | |
198 | .Fn putenv | |
199 | function appeared in | |
200 | .Bx 4.3 Reno . | |
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201 | .Pp |
202 | Until | |
203 | .Fx 7.0 , | |
204 | .Fn putenv | |
205 | would make a copy of | |
206 | .Fa string | |
207 | and insert it into the environment using | |
208 | .Fn setenv . | |
209 | This was changed to use | |
210 | .Fa string | |
211 | as the memory location of the ``name=value'' pair to follow the | |
212 | .Tn POSIX | |
213 | specification. | |
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214 | .Sh BUGS |
215 | Successive calls to | |
216 | .Fn setenv | |
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217 | that assign a larger-sized |
218 | .Fa value | |
219 | than any previous value to the same | |
220 | .Fa name | |
221 | will result in a memory leak. | |
222 | The | |
9bb2a92d | 223 | .Dx |
5d0641a4 | 224 | semantics for this function |
984263bc | 225 | (namely, that the contents of |
5d0641a4 | 226 | .Fa value |
984263bc | 227 | are copied and that old values remain accessible indefinitely) make this |
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228 | bug unavoidable. |
229 | Future versions may eliminate one or both of these | |
984263bc | 230 | semantic guarantees in order to fix the bug. |