Another common need is for programs to honor per-user configurations. At start-up time, a program
might apply reasonable global defaults and then read a user??™s configuration file to apply, say, a
custom color scheme.
There are also a number of per-user settings, such as environment variables, that programs need to
know how to accommodate. For example, the $MAIL environment variable identifies where the
user??™s mail spool file is kept, and the $VISUAL environment variable defines the user??™s preferred full
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Programming in Linux Part VI
screen editor (which all true Linux users know is vi). The $PRINTER environment variable stores
the name of the user??™s default printer and, of course, $HOME identifies the user??™s home directory.
In a pervasively multiuser system such as Linux, programs and programmers must always take into
account that most resources a program might want to use are usually shared. Likewise, they must
also take into account that most real-world usage scenarios (more formally known as use cases)
assume that multiple instances of the program are running at the same time.
Interprocess Communication
Interprocess communication (IPC) enables programs to share data and resources with a minimum
amount of overhead and is used extensively on all Linux systems.
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