Hi,
On the second line of $_, there's a number of whitespace characters that precede "barney" - hence that line does not begin with "barney":

$_ = 'This is a wilma line
       barney is on this line
       but this line ends with fred
       and a final dino line' ;
      
if (/^barney/m) { 
  print "Found barney \n";
} else {
  print "Barney not found \n";
}

$_ = 'This is a wilma line
barney is on this line
but this line ends with fred
and a final dino line' ;
      
if (/^barney/m) { 
  print "Found barney \n";
} else {
  print "Barney not found \n";
}

__END__

Outputs:

Barney not found
Found barney
[download]

Cheers,
Rob