Re: query-replace-regexp on a string with '=' sign

[Tassilo Horn]

Pankaj Jangid <pankaj@codeisgreat.org> writes:

>>> I have a line like this,
>>>   HELLO=WORLD
>>> now I want to downcase the part before the equal (=) sign.
>>> I am approaching like this
>>>
>>>  M-x query-replace-regexp RET \(.+\)= RET \,(downcase \1)= RET
>>>
>>> But this doesn't work.
>>
>> Where "doesn't work" means "doesn't downcase but keeps HELLO", right?
>
> Yes. Suppose I have these lines in a region
> HELLO=WORLD
> HELLOXXXXWORLD
> and if I now execute following sequence,
> M-x query-replace-regexp RET \(.+\)= RET \,(downcase \1)= RET
> the output is,
>
> hello=WORLD
> HELLOXXXXWORLD

For me (with emacs -Q on the current master), it stays as it is, i.e.,
all caps.

> but if I execute this,
> M-x query-replace-regexp RET \(.+\)XXXX RET \,(downcase \1)XXXX RET
> then the output is,
>
> HELLO=WORLD
> helloXXXXWORLD

I can reproduce that.  I think that's documented on the info page I've
cited.  When the replacement is all lower- or all uppercase (like
hello=), `case-replace' has an effect.  But when the replacement is
mixed-case (like helloXXXX), case will be preserved.

>> Have a look at (info "(emacs) Replacement and Lax Matches") which
>> explains it.  I think the default `case-replace' value of t is the
>> problem here.
>
> Thanks for pointing me to the right direction. Understood case-replace
> thing. But the one thing that is still not clear to me is that, why
> the first command doesn't downcase HELLO in the first line, whereas
> the second command downcases the HELLO in the second line.

Huh?  You've said the first command does downcase hello in the first
line although I cannot reproduce that and would not have an explanation
for that behavior.  If it's actually the same for you, then see my last
paragraph for the explanation.

Bye,
Tassilo