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getenv(3) [freebsd 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

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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 putenv(char *string); int setenv(const char *name, const char *value, int overwrite); 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 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 variable, name. 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 string pointed to by string becomes part of the environment. A program should not alter or free the string, and should not use stack or other transient string variables as arguments to putenv(). The setenv() function is strongly preferred to putenv(). The unsetenv() function deletes all instances of the variable name pointed to by name from the list. Note that only the variable name (e.g., "NAME") should be given; "NAME=value" will not work. 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 unsetenv() failed because name was not found in the environment list. [ENOMEM] The function setenv() or putenv() failed because it was unable to allocate memory for the environment. LEGACY SYNOPSIS
#include <stdlib.h> void unsetenv(const char *name); unsetenv() doesn't return a value. COMPATIBILITY
putenv() no longer copies its input buffer. This often appears in crash logs as a crash in getenv(). Avoid passing local buffers or freeing the memory that is passed to putenv(). Use setenv(), which still makes an internal copy of its buffers. unsetenv() no longer parses the variable name; e.g., unsetenv ("FOO=BAR") no longer works. Use unsetenv("FOO"). unsetenv() also now returns a status value and will set errno to EINVAL if name is not a defined environment variable. SEE ALSO
csh(1), sh(1), execve(2), compat(5), environ(7) STANDARDS
The getenv() function conforms to ISO/IEC 9899:1990 (``ISO C90''). BUGS
Successive calls to setenv() or putenv() assigning a differently sized value to the same name will result in a memory leak. The FreeBSD semantics for these functions (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. HISTORY
The functions setenv() and unsetenv() appeared in Version 7 AT&T UNIX. The putenv() function appeared in 4.3BSD-Reno. BSD
December 11, 1993 BSD

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