1:31 >perl -wE "my $constant = 'fred'; my $string = 'fredflintstone'; print qq[found $1\n] if $string =~ /^$constant/;"
Use of uninitialized value $1 in concatenation (.) or string at -e line 1.
found

 1:32 >perl -wE "my $constant = 'fred'; my $string = 'fredflintstone'; print qq[found $1\n] if $string =~ /^($constant)/;"
found fred

 1:32 >