CSH Help -- I don't get it ...

[Michael Greim]

Ok, Damian, my posting was unclear.
Thanks for pointing it out. (I still have much to learn :-)

In article <1170003 at otter.hple.hp.com>, pdc at otter.hple.hp.com (Damian Cugley) writes:
> / comp.unix.questions / greim at sbsvax.UUCP (Michael Greim) /  Aug  8, 1988 /
> 
> > < if "$x" =~ "stuff*" echo yes
> > < alias x 'if "$x" =~ "stuff*" echo yes'
> > < x
> > < alias x 'if "$x" =~ "stuff"* echo yes'
> > < x
> > <     It only prints 'yes' once -- on try three.
> > It's a bug in csh or at least an undocumented strangeness.
> 
> It may not be a bug. It *is* consistent with the rest of csh.
Yes, this may not be a bug. Let's stick to that it is not a bug.
     ^^^^
(So nobody needs a fix, nobody has to work one out, and
all versions of csh behave the same :-)
> 
> "..."  quoting prevents pattern patching when expanding filenames in
> commands, so it makes sense for the same to happen when using patterns
> with =~ or !~.  
Ok.
> 
> > In your first example the string resulting from expanding "$x" has
> > no 8 bit turned on, but the string "stuff*" has. Thus "*" is not recognized
> > as a shell meta character.
> 
> I don't think this makes much sense to me - I wonder what the person
> asking the question made of it :-( .  The * isn't recognised as being
> magical because it is quoted (i.e.  in "...").  Exactly how csh keeps
> track of what's quoted and what isn't is beside the point.
Sorry.
> 
> >                             A fix I made some months ago and posted to the
> > net took care of this bug, I think. It was listed as <486 at sbsvax.UUCP>
> > from 25.apr.88. But there were still some flaws in pattern matching
> > which it might even be impossible to straighten out.
> 
> I don't *think* it's a bug (I don't claim to be an expert).  In the man
> page for csh it says "..."  prevents filename expansion, i.e. makes *
> unmagical.  It should've said it made it unmagic in =~ patterns too, but
> that's a reasonable deduction.  
> 
> Why would it be useful for pattern-matching to work even when quoted?
> How then would we turn it *off*!?  If there's no bug, 'fixing' it will
> only cause more problems (i.e. introduce more bugs...).
I have made a modification to pattern matching, where
a pattern is command- and filename- expanded like any other operand.
"abc*" is a pattern matching abc, abcd, ... but "abc\*" only matches
the string "abc*". Ok, it introduces more problems and its usefulness
is at least doubtful. That's one of the reasons why I have not posted it.
(And I could not make myself to write a small text on the differences)

The bug fix I mentioned above was for another but similar problem
(my, am I confused lately :-), viz.:
	- create files "a,b" and "abc"
	- try to list these two files using "{" and "}" filename expansion
		metacharacters as in the example below
Script started on Fri Aug 12 10:48:16 1988
% ls
a,c		abc		typescript
% ls a{b,,}c
ac not found
ac not found
abc
% ls a{b,\,}c
ac not found
ac not found
abc
% ls a{b,","}c
ac not found
ac not found
abc
% ls a{b,','}c
ac not found
ac not found
abc
% 
And so on. The above cited fix was for this problem. Afterwards
% ls a{b,\,}c
produced the correct output :
a,c	abc
The same applies to metacharacters "[", "-" and "]".
This problem is about pattern matching but besides the point
of this discussion.
> 
> > BTW:
> > Did you ever wonder why 'if "$x" =~ "stuff"*' does not try to do
> > any filename substitution? The big question is : should it ?
> 
> No, I didn't wonder.  No, it shouldn't.  'If's are special csh keywords,
> and the test part isn't a command; hence there's no reason whatsoever
> why it should try to expand patterns into filenames in the test part of
> an 'if'.
But it expands other operands. Try :
#! /bin/csh
if ( Gargle* =~ "Gargle"*) then
	echo "1 : ok."
else
	echo "1 : false."
endif
and you will see, that csh filename expands the left operand of "=~".

BTW:
And why is the pattern not command substituted? Does the manual say
so? Should it not be possible to
	if ( "$a" =~ *`hostname`*) ...
whereas
	if ( "$a" == `hostname` ) ...
works ??
(You may not have noticed this, as it produces no diagnostic message.)
Ok, you can circumvent it, but isn't it a bug? Or is it no bug, if
it would have been documented?

The manual should be extended to say some lines about patterns in
csh expressions.
One can adapt to a lot of strange rules if they are documented.

	-mg
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