Some environment variables are deﬁned by POSIX.1 in the Single UNIX Speciﬁcation, whereas others are deﬁned only if the XSI option is supported. Figure 7.7 lists the environment variables deﬁned by the Single UNIX Speciﬁcation and notes which implementations support the variables. Any environment variable deﬁned by POSIX.1 is marked with •; otherwise, it is part of the XSI option. Many additional implementation-dependent environment variables are used in the four implementations described in this book. Note that ISO C doesn’t deﬁne any environment variables.
Are the environment variables defined by POSIX for a shell, or for any process which doesn't necessarily run shell?
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