GETENV(3) BSD Programmer's Manual GETENV(3)
getenv, putenv, setenv, unsetenv - environment variable functions
#include <stdlib.h> char * getenv(const char *name); int setenv(const char *name, const char *value, int overwrite); int putenv(const char *string); int unsetenv(const char *name);
These functions set, unset, and fetch environment variables from the host environment list. For compatibility with differing environment conven- tions, the given arguments name and value may be appended and prepended, respectively, with an equal sign "=". The getenv() function obtains the current value of the environment vari- able name. If the variable name is not in the current environment, a null pointer is returned. The setenv() function inserts or resets the environment variable name in the current environment list. If the variable name does not exist in the list, it is inserted with the given value. If the variable does exist, the argument overwrite is tested; if overwrite is zero, the variable is not reset, otherwise it is reset to the given value. The putenv() function takes an argument of the form name=value and is equivalent to: setenv(name, value, 1); The unsetenv() function deletes all instances of the variable name point- ed to by name from the list.
The functions setenv(), putenv(), and unsetenv() return zero if success- ful; otherwise the global variable errno is set to indicate the error and -1 is returned. If getenv() is successful, the string returned should be considered read-only.
[ENOMEM] The function setenv() or putenv() failed because they were unable to allocate memory for the environment. [EINVAL] The function unsetenv() failed because the argument was a NULL pointer, an empty string, or a string containing an '=' character.
csh(1), sh(1), execve(2), environ(7)
The getenv() function conforms to ANSI X3.159-1989 ("ANSI C"). The unsetenv() function conforms to Version 3 of the Single UNIX Specification.
The function getenv() appeared in Version 7 AT&T UNIX and 3BSD. The func- tions setenv() and unsetenv() appeared in 4.3BSD-Tahoe. The putenv() function appeared in 4.3BSD-Reno. MirOS BSD #10-current December 11, 1993 1
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