getenv(3) - NetBSD Manual Pages

GETENV(3)               NetBSD 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(const 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 conven- tions, the given arguments name and value may be appended and prepended, respectively, with an equal sign ``='', except for unsetenv(). 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 pointed to by name from the list.
RETURN VALUES
The functions setenv(), putenv() and unsetenv() return zero if success- ful; otherwise the global variable errno is set to indicate 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 unsetenv() is a null pointer, points to an empty string, or points to a string con- taining an ``='' character. [ENOMEM] The function setenv() 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 ANSI X3.159-1989 (``ANSI C''). 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. NetBSD 2.0 April 1, 2003 NetBSD 2.0

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