Unix Programming - Environment Variables - User Environment Variables
User Environment Variables
Although applications are free to interpret environment
variables outside the system-defined set, it is nowadays fairly
unusual to actually do so. Environment values are not really suitable
for passing structured information into a program (though it can in
principle be done via parsing of the values). Instead, modern Unix
applications tend to use run-control files and dotfiles.
There are, however, some design patterns in which user-defined
environment variables can be useful:
Application-independent preferences that need to be
shared by a large number of different programs. This set of
‘standard’ preferences changes only slowly, because lots
of different programs need to recognize each one before it becomes
useful.[102] Here are the standard ones:
EDITOR
The name of the user's preferred editor (often used by shellout
commands).[103]
MAILER
The name of the user's preferred mail user agent (often used by
shellout commands).
PAGER
The name of the
user's preferred program for browsing plaintext.
BROWSER
The name of the
user's preferred program for browsing Web URLs. This one, as of
2003, is still very new and not yet widely
implemented.
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