Question

I have an input field which should accept only letters (doesn’t matter lower or uppercase).
I could write this simply by using co ca (contains only/any) operator. But it’s time consuming.

  if p_input3 ca '*/ + - ? ! % ( ) = 0123456789'.
    MESSAGE e000 WITH 'Only letters are allowed. No numbers or special characters'.
  ENDIF.

It works. But I wanted to check it using regex.
I tried this code. But It doesn’t work quite well.

DATA: text TYPE string,
      matcher type REF TO cl_abap_matcher.

PARAMETERS: p_input3 TYPE string DEFAULT 'abCD*()fhi' LOWER CASE.

matcher = cl_abap_matcher=>create(
   pattern = `([a-zA-Z])`
    text = p_input3
  ).

  if matcher = abap_true.
    MESSAGE e000 with 'Only letters are allowed. No numbers or special characters'.
  ENDIF.

Could anyone figure it out?

Answer 1

First, your regular expression won’t work. It is only successful when your input contains only a single letter.

This one will work correctly:

'[a-zA-Z]*'

+ and * mean repetition. That means a chain of any number of characters which falls into the preceding category. The difference is that * can also mean 0 times, while + means at least one time. So an empty string would match [a-z]* but not [a-z]+

Then you are checking the reference to the matcher object itself for being equal to abap_true. This won’t ever happen, because it will always be a reference to a matcher object, not abap_true or abap_false.

To get the result of a match, you have to not just create the matcher but actually run it by calling its match method.

IF matcher->match( ) = abap_false.
    MESSAGE e000 with 'Only letters are allowed. No numbers or special characters'.      
ENDIF. 

But there is also a much easier way to do this with the FIND REGEX command instead of the class cl_abap_matcher:

FIND FIRST OCCURRENCE OF REGEX '[^a-zA-Z]' IN p_input3.
IF sy-subrc = 0.
    MESSAGE 'There is some non-letter in your input.' TYPE 'E'.
ENDIF.

^ means negation. So [^a-zA-Z] means any character which is NOT in the given range.