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| 32 | .\" @(#)getenv.3 8.2 (Berkeley) 12/11/93 |
| 33 | .\" $FreeBSD: src/lib/libc/stdlib/getenv.3,v 1.27 2007/07/04 00:00:39 scf Exp $ |
| 34 | .\" $DragonFly: src/lib/libc/stdlib/getenv.3,v 1.5 2006/02/17 19:35:06 swildner Exp $ |
| 35 | .\" |
| 36 | .Dd June 20, 2007 |
| 37 | .Dt GETENV 3 |
| 38 | .Os |
| 39 | .Sh NAME |
| 40 | .Nm getenv , |
| 41 | .Nm putenv , |
| 42 | .Nm setenv , |
| 43 | .Nm unsetenv |
| 44 | .Nd environment variable functions |
| 45 | .Sh LIBRARY |
| 46 | .Lb libc |
| 47 | .Sh SYNOPSIS |
| 48 | .In 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 "char *string" |
| 55 | .Ft int |
| 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 | .Pp |
| 62 | The |
| 63 | .Fn getenv |
| 64 | function obtains the current value of the environment variable, |
| 65 | .Fa name . |
| 66 | The application should not modify the string pointed |
| 67 | to by the |
| 68 | .Fn getenv |
| 69 | function. |
| 70 | .Pp |
| 71 | The |
| 72 | .Fn setenv |
| 73 | function inserts or resets the environment variable |
| 74 | .Fa name |
| 75 | in the current environment list. |
| 76 | If the variable |
| 77 | .Fa name |
| 78 | does not exist in the list, |
| 79 | it is inserted with the given |
| 80 | .Fa value . |
| 81 | If the variable does exist, the argument |
| 82 | .Fa overwrite |
| 83 | is tested; if |
| 84 | .Fa overwrite |
| 85 | is zero, the |
| 86 | variable is not reset, otherwise it is reset |
| 87 | to the given |
| 88 | .Fa value . |
| 89 | .Pp |
| 90 | The |
| 91 | .Fn putenv |
| 92 | function takes an argument of the form ``name=value'' and |
| 93 | puts it directly into the current environment, |
| 94 | so altering the argument shall change the environment. |
| 95 | If the variable |
| 96 | .Fa name |
| 97 | does not exist in the list, |
| 98 | it is inserted with the given |
| 99 | .Fa value . |
| 100 | If the variable |
| 101 | .Fa name |
| 102 | does exist, it is reset to the given |
| 103 | .Fa value . |
| 104 | .Pp |
| 105 | The |
| 106 | .Fn unsetenv |
| 107 | function |
| 108 | deletes all instances of the variable name pointed to by |
| 109 | .Fa name |
| 110 | from the list. |
| 111 | .Sh RETURN VALUES |
| 112 | The |
| 113 | .Fn getenv |
| 114 | function returns the value of the environment variable as a |
| 115 | .Dv NUL Ns |
| 116 | -terminated string. |
| 117 | If the variable |
| 118 | .Fa name |
| 119 | is not in the current environment, |
| 120 | .Dv NULL |
| 121 | is returned. |
| 122 | .Pp |
| 123 | .Rv -std setenv putenv unsetenv |
| 124 | .Sh ERRORS |
| 125 | .Bl -tag -width Er |
| 126 | .It Bq Er EINVAL |
| 127 | The function |
| 128 | .Fn getenv , |
| 129 | .Fn setenv |
| 130 | or |
| 131 | .Fn unsetenv |
| 132 | failed because the |
| 133 | .Fa name |
| 134 | is a |
| 135 | .Dv NULL |
| 136 | pointer, points to an empty string, or points to a string containing an |
| 137 | .Dq Li \&= |
| 138 | character. |
| 139 | .Pp |
| 140 | The function |
| 141 | .Fn putenv |
| 142 | failed because |
| 143 | .Fa string |
| 144 | is a |
| 145 | .Dv NULL |
| 146 | pointer, |
| 147 | .Fa string is without an |
| 148 | .Dq Li \&= |
| 149 | character or |
| 150 | .Dq Li \&= |
| 151 | is the first character in |
| 152 | .Fa string . |
| 153 | This does not follow the |
| 154 | .Tn POSIX |
| 155 | specification. |
| 156 | .It Bq Er ENOMEM |
| 157 | The function |
| 158 | .Fn setenv , |
| 159 | .Fn unsetenv |
| 160 | or |
| 161 | .Fn putenv |
| 162 | failed because they were unable to allocate memory for the environment. |
| 163 | .It Bq Er EFAULT |
| 164 | The functions |
| 165 | .Fn setenv , |
| 166 | .Fn unsetenv |
| 167 | or |
| 168 | .Fn putenv |
| 169 | failed to make a valid copy of the environment due to the environment being |
| 170 | corrupt (i.e., a name without a value). A warning will be output to stderr with |
| 171 | information about the issue. |
| 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 . |
| 183 | The |
| 184 | .Fn setenv , |
| 185 | .Fn putenv |
| 186 | and |
| 187 | .Fn unsetenv |
| 188 | functions conforms to |
| 189 | .St -p1003.1-2001 . |
| 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 . |
| 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. |
| 214 | .Sh BUGS |
| 215 | Successive calls to |
| 216 | .Fn setenv |
| 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 |
| 223 | .Dx |
| 224 | semantics for this function |
| 225 | (namely, that the contents of |
| 226 | .Fa value |
| 227 | are copied and that old values remain accessible indefinitely) make this |
| 228 | bug unavoidable. |
| 229 | Future versions may eliminate one or both of these |
| 230 | semantic guarantees in order to fix the bug. |