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(standards.info)User Interfaces

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Standards for Interfaces Generally
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   Please don't make the behavior of a utility depend on the name used
to invoke it.  It is useful sometimes to make a link to a utility with
a different name, and that should not change what it does.

   Instead, use a run time option or a compilation switch or both to
select among the alternate behaviors.

   Likewise, please don't make the behavior of the program depend on the
type of output device it is used with.  Device independence is an
important principle of the system's design; do not compromise it merely
to save someone from typing an option now and then.  (Variation in error
message syntax when using a terminal is ok, because that is a side issue
that people do not depend on.)

   If you think one behavior is most useful when the output is to a
terminal, and another is most useful when the output is a file or a
pipe, then it is usually best to make the default behavior the one that
is useful with output to a terminal, and have an option for the other
behavior.

   Compatibility requires certain programs to depend on the type of
output device.  It would be disastrous if `ls' or `sh' did not do so in
the way all users expect.  In some of these cases, we supplement the
program with a preferred alternate version that does not depend on the
output device type.  For example, we provide a `dir' program much like
`ls' except that its default output format is always multi-column
format.