[bhl]

There are some http server plugins that can automatically correct for incorrect case.
So you could request http://foo.com/ABC.html
So you could request http://foo.com/abc.html
and the file ABC, abc, or even Abc.html will get served.

That said, grep would do the trick.

But since html and http are (usually/conventionally) lower case, you could just go through the files and convert them all to lower case.

Always work on a copy.. easy to make a mistake or not catch an edge case that breaks everything.

If you get stuck, you can always request some help on fiverr or upwork (a job like that might be $15.)

[bhl]

Oh, just saw you're using Apache. Try enabling the spell check module: CheckSpelling On CheckCaseOnly On

[daniel1212]

"But since html and http are (usually/conventionally) lower case, you could just go through the files and convert them all to lower case."

Again, I can find all the links, but looking for and changing maybe hundreds one by one takes a lot of time.