Use Data Extension value in AMPScript regex

Question

Are Data Extension variables merged before AMPScript is run? E.g. I want to see if a data extension variable for the current recipient contains part of a string:

%%[
var @result
SET @result = RegExMatch("A String", ".*(\|%%DATAEXT_VAR%%\|).*", 1)
IF Length(@result) > 0 THEN]%%
  ... show HTML here ...
%%[ ENDIF ]%%

This doesn't work. Does the regular expression need assembling using CONCAT, or the variable needs to be accessed via Field() or similar? I have not found documentation covering this.

Answer 1

I'd recommend not using raw send context variables. I generally check them first with the AttributeValue() function:

%%[
var @result, @regextouse, @data_ext_var

set @data_ext_var = AttributeValue("DATAEXT_VAR")

if not empty(@data_ext_var) then

    SET @regextouse = CONCAT(".*(\|", @data_ext_var, "\|).*")
    SET @result = RegExMatch("A String", @regextouse, 1)

    IF Length(@result) > 0 THEN
    ]%%
      ... show HTML here ...

    %%[ ENDIF ]%%

%%[ ENDIF ]%%

May not be a big deal in your case, but if there's any fluidity in the data extension columns, then it's a good idea. Many of the AMPScript functions don't handle null values very well. The AttributeValue() function returns an empty string in that case.

Answer 2

Cracked it. You do need to use CONCAT:

%%[
var @result, @regextouse
SET @regextouse = CONCAT(".*(\|", DATAEXT_VAR, "\|).*")
SET @result = RegExMatch("A String", @regextouse, 1)
IF Length(@result) > 0 THEN]%%
  ... show HTML here ...
%%[ ENDIF ]%%