ruby – Replace a long case statement involving regex with a hash

I would use a single regex and a hash code that does not use regex, just the output of a
single regex match to do the code lookup.

Demo : www.jdoodle.com/ia/1NBq

file_types = {
    'camt.053.001' => 'camt053',
    'camt.052.001' => 'camt052',
    '"Auftragskonto";"Buchungstag";"Valutadatum";' => 'SpK'
}

RxFileTypes = /(?:camt\.053\.001|camt\.052\.001\.08|"Auftragskonto";"Buchungstag";"Valutadatum";)/
first_bytes="

Output

File type code is :  camt053    

Combine all the file types into a single regex separated by alternations.
The match will be the Key into the File Type code hash.

(?:
   camt \. 053 \. 001
 | camt \. 052 \. 001 \. 08
 | "Auftragskonto";"Buchungstag";"Valutadatum";
)

For additional File types just add another alternation and an entry into the File Type code hash.