Is this what you’re looking for?

#! perl
use strict;
use warnings;

my @strings = ('ECX3', 'ABC3X 98', 'A B3X 28.5');

for (@strings)
{
    print "$1\n" if /([a-zA-Z]{1,2})/;
}
[download]

Output:

13:13 >perl 633_SoPW.pl
EC
AB
A

13:13 >
[download]

If your requirements are more complex, please explain exactly what is needed.

Hope that helps,