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 5.10 24 Jul 2002 getenv(3C)
Check Out this Related Man Page
GETENV(3) BSD Library Functions Manual GETENV(3)NAME
getenv, getenv_r, putenv, setenv, unsetenv -- environment variable functions
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdlib.h>
char *
getenv(const char *name);
int
getenv_r(const char *name, char *buf, size_t len);
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. For compatibility with differing environment con-
ventions, the getenv() or getenv_r() given argument name may be appended with an equal sign ``=''.
The getenv() function obtains the current value of the environment variable name. If the variable name is not in the current environment, a
NULL pointer is returned.
The getenv_r() function obtains the current value of the environment variable name and copies it to buf. If name is not in the current envi-
ronment, or the string length of the value of name is longer than len characters, then -1 is returned and errno is set to indicate the error.
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 it will set the environment variable ``name'' equal to ``value'' by
altering an existing entry, or creating a new one if an existing one does not exist. The actual string argument passed to putenv() will
become part of the environment. If one changes the string, the environment will also change.
The unsetenv() function deletes all instances of the variable name pointed to by name from the list.
RETURN VALUES
The functions getenv_r(), setenv(), putenv(), and unsetenv() return zero if successful; otherwise the global variable errno is set to indi-
cate the error and a -1 is returned.
If getenv() is successful, the string returned should be considered read-only.
ERRORS
[EINVAL] The name argument to setenv() or unsetenv() is a null pointer, points to an empty string, or points to a string containing
an ``='' character. The value argument to setenv() is a null pointer. The string argument to putenv() is a null pointer,
or points to a string that either starts with a ``='' character or does not contain one at all.
[ENOMEM] The function setenv() or putenv() failed because they were unable to allocate memory for the environment.
The function getenv_r() can return the following errors:
[ENOENT] The variable name was not found in the environment.
[ERANGE] The value of the named variable is too long to fit in the supplied buffer.
SEE ALSO csh(1), sh(1), execve(2), environ(7)STANDARDS
The getenv() function conforms to ANSI X3.159-1989 (``ANSI C89''). The putenv() function conforms to X/Open Portability Guide Issue 4
(``XPG4''). The unsetenv() function 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.
BSD October 25, 2010 BSD