getenv(3C) Standard C Library Functions getenv(3C)NAME
getenv - return value for environment name
SYNOPSIS
#include <stdlib.h>
char *getenv(const char *name);
DESCRIPTION
The getenv() function searches the environment list (see environ(5)) for a string of the form name=value and, if the string is present,
returns a pointer to the value in the current environment.
RETURN VALUES
If successful, getenv() returns a pointer to the value in the current environment; otherwise, it returns a null pointer.
USAGE
The getenv() function can be safely called from a multithreaded application. Care must be exercised when using both getenv() and
putenv(3C) in a multithreaded application. These functions examine and modify the environment list, which is shared by all threads in an
application. The system prevents the list from being accessed simultaneously by two different threads. It does not, however, prevent two
threads from successively accessing the environment list using getenv() or putenv(3C).
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Standard |
+-----------------------------+-----------------------------+
|MT-Level |Safe |
+-----------------------------+-----------------------------+
SEE ALSO exec(2), putenv(3C), attributes(5), environ(5), standards(5)SunOS 5.11 24 Jul 2002 getenv(3C)
Check Out this Related Man Page
GETENV(3) BSD Library Functions Manual GETENV(3)NAME
getenv, putenv, setenv, unsetenv -- environment variable functions
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdlib.h>
char *
getenv(const char *name);
int
setenv(const char *name, const char *value, int overwrite);
int
putenv(char *string);
int
unsetenv(const char *name);
DESCRIPTION
These functions set, unset and fetch environment variables from the host environment list.
The getenv() function obtains the current value of the environment variable, name. The application should not modify the string pointed to
by the getenv() function.
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 puts it directly into the current environment, so altering the argu-
ment shall change the environment. If the variable name does not exist in the list, it is inserted with the given value. If the variable
name does exist, it is reset to the given value.
The unsetenv() function deletes all instances of the variable name pointed to by name from the list.
If corruption (e.g., a name without a value) is detected while making a copy of environ for internal usage, then setenv(), unsetenv() and
putenv() will output a warning to stderr about the issue, drop the corrupt entry and complete the task without error.
RETURN VALUES
The getenv() function returns the value of the environment variable as a NUL-terminated string. If the variable name is not in the current
environment, NULL is returned.
The setenv(), putenv(), and unsetenv() functions return the value 0 if successful; otherwise the value -1 is returned and the global variable
errno is set to indicate the error.
ERRORS
[EINVAL] The function getenv(), setenv() or unsetenv() failed because the name is a NULL pointer, points to an empty string, or
points to a string containing an ``='' character.
The function putenv() failed because string is a NULL pointer, string is without an ``='' character or ``='' is the first
character in string. This does not follow the POSIX specification.
[ENOMEM] The function setenv(), unsetenv() or putenv() failed because they were unable to allocate memory for the environment.
SEE ALSO csh(1), sh(1), execve(2), environ(7)STANDARDS
The getenv() function conforms to ISO/IEC 9899:1990 (``ISO C90''). The setenv(), putenv() and unsetenv() functions conforms to IEEE Std
1003.1-2001 (``POSIX.1'').
HISTORY
The functions setenv() and unsetenv() appeared in Version 7 AT&T UNIX. The putenv() function appeared in 4.3BSD-Reno.
Until FreeBSD 7.0, putenv() would make a copy of string and insert it into the environment using setenv(). This was changed to use string as
the memory location of the ``name=value'' pair to follow the POSIX specification.
BUGS
Successive calls to setenv() that assign a larger-sized value than any previous value to the same name will result in a memory leak. The
FreeBSD semantics for this function (namely, that the contents of value are copied and that old values remain accessible indefinitely) make
this bug unavoidable. Future versions may eliminate one or both of these semantic guarantees in order to fix the bug.
BSD June 20, 2007 BSD