Question

How would I detect if a string contained for instance my first name but not my last name using only a regular expression?

Answer 1

The easiest way to use regular expressions for this is to use simple regexes and logical connectives. Since you only want simple matches and since you didn’t list a language, here is a basic implementation in Perl:

my $str1="firstname lastname blah blah blah";
my $str2="blurg firstname etc";

foreach($str1,$str2)
{
  if(/firstname/ and !/lastname/)
  {
    print "$_ matched firstname and not lastname!\n";
  }
  else
  {
    print "No match for $_\n";
  }
}

As expected, the output is:

No match for firstname lastname blah blah blah
blurg firstname etc matched firstname and not lastname!