Searches in HoudahSpot are case insensitive.
One way to do a case sensitive search is to use HoudahSpot to build a Spotlight query and then use that query with the mdfind tool at the command line in Terminal.app.
There is an undocumented feature in the HoudahSpot 4 search field that allows you to run case sensitive searches. This feature is intentionally undocumented since it is still subject to change. It also suffers from the same problem all automagical search fields share: you have to get the syntax exactly right to get the results you want. In HoudahSpot you can use Window > Raw Query to see the resulting Spotlight query. This should allow you to determine if HoudahSpot understood your search or not.
Basically, the HoudahSpot search field allows you to append Spotlight search modifiers (see the above blog post) to search values. You would search for:
This will search for file names ending in .license. It will ignore diacritical marks, but respect case. This will produce the following raw query:
kMDItemFSName = "*.license"d
The HoudahSpot “File Extension” criterion, which is case insensitive, produces the following raw query:
kMDItemFSName = "*.license"cd
If you leave off the modifier, the HoudahSpot search field will default to a case insensitive, diacritical mark insensitive word search. This search:
filename:"*.license"is equivalent to this raw Spotlight query:
kMDItemFSName = "*.license"cdw
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