Trap of matching by string variable in Perl

　　When you want to match a continuous string by string variable, just append parenthesises between variable!

use 5.010 ;


$_ = 'ababababab1212abab12abab' ;
$var = 'ab' ;

m/^$var+/ ;          # m/^ab+/ : mismatch
say 'm/^$var+/' ;
say '$` = '.$` ;
say '$& = '.$& ;
say '$\' = '.$' ;

say '---------' ;

m/^($var+)/ ;        # m/^ab+/ : mismatch
say 'm/^($var+)/' ;
say '$` = '.$` ;
say '$& = '.$& ;
say '$\' = '.$' ;

say '---------' ;

m/^($var)+/ ;        # m/^(ab)+/ : ok
say 'm/^($var)+/' ;
say '$` = '.$` ;
say '$& = '.$& ;
say '$\' = '.$' ;

say '---------' ;

m/^(ab)+/ ;          # m/^(ab)+/ : ok
say 'm/^(ab)+/' ;
say '$` = '.$` ;
say '$& = '.$& ;
say '$\' = '.$' ;