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