environ(7)用户环境

environ 是 UNIX 下的一个全局变量。
指向一个字符类型的指针数组。
每个数组元素是一个 “name=value” 形式的字符串。
数组以 NULL 指针结尾。
使用前应先声明：

extern char **environ;

有些类 UNIX 操作系统将环境变量作为main函数的第3个参数，但由于它其实是全局变量，因此没有必要。

与其相关的库函数有

clearenv(3)getenv(3)putenv(3)setenv(3)unsetenv(3)

环境变量举例如下：

LOGNAME
The name of the logged-in user (used by some System-V derived programs).

HOME A user’s login directory, set by login(1) from the password file passwd(5).

LANG The name of a locale to use for locale categories when not overridden by
LC_ALL or more specific environment variables like LC_COLLATE, LC_CTYPE,
LC_MESSAGES, LC_MONETARY, LC_NUMERIC, LC_TIME, cf. locale(5).

PATH The sequence of directory prefixes that sh(1) and many other programs apply
in searching for a file known by an incomplete pathname. The prefixes are
separated by ‘:’. (Similarly one has CDPATH used by some shells to find the
target of a change directory command, MANPATH used by man(1) to find manual
pages, etc.)

PWD The current working directory. Set by some shells.

SHELL The pathname of the user’s login shell.

TERM The terminal type for which output is to be prepared.

PAGER The user’s preferred utility to display text files.