[bug #22109] Enhancement request: tr should be able to take multiple consecutive actions

[James Youngman]

Follow-up Comment #1, bug #22109 (project coreutils):

Could you provide some more justification than "would be nice" please?

Implementing the change you suggest would significantly complicate the
implementation of tr, which is already quite fearsome; see for example the
recent discussion of the correct processing of "tr [:lower:] [:upper:]" in
locales where the number of upper-case letters is different to the number of
lower-case letters.   

Such additional complexity doesn't come for free.  Somebody has to implement
it, the coreutils maintainers have to take the time to understand the new
implementation, they have to maintain and fix bugs in it.   Then the Info
documentation and the manual page need to be updated to explain the changed
functionality in such a way that any corner-cases are identified.   For
example, what does this do?  

tr -dc ABC -s

Does that do the same as this?

tr -d ABC -c -s

What about "tr -d ABC -c -s 123"?  Is 123 SET1 or SET2?  

I think the documentation task will be non-trivial.  Non-trivial
documentation will probably result, making it harder for people to understand.
 So everybody gets harder-to-understand documentation in the name of a
convenience feature.

The complex documentation and more complex implementation opens an
opportunity for the documentation to describe something slightly different to
the implementation.  When somebody notices the problem, which should get
fixed?

But this feature could indeed be convenient.  It could be sufficiently
convenient for many people to use it a lot.   Who will field their questions
when their script doesn't work - or silently does something different - on
other systems?

In summary, maybe nobody should change any piece of software, ever.   Except
maybe to fix bugs.  Carefully.  :)


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