Note that this will deal with Mary and her little lamb over any line boundaries:
c:\@Work\Perl\monks>perl
use strict;
use warnings;
use autodie;
my $data = <<EOD;
Mary Had
A Little Lamb She
Was GOOD
Not Changing this
Or This
Mary Had A Little
Lamb She Was GOOD
Line 9
Line 10
EOD
open my $fh, '<', \$data;
my $content = do { local $/; <$fh>; };
print "[[$content]] \n\n";
$content =~
s{ Mary \s+ Had \s+ A \s+ Little \s+ Lamb \s+ She \s+ Was \s+ GOOD }
{CHANGED!!!}xmsg;
print "<<$content>> \n";
__END__
[[Mary Had
A Little Lamb She
Was GOOD
Not Changing this
Or This
Mary Had A Little
Lamb She Was GOOD
Line 9
Line 10
]]
<<CHANGED!!!
Not Changing this
Or This
CHANGED!!!
Line 9
Line 10
>>
Give a man a fish: <%-{-{-{-<