while ($line .= <Stream>) 
{ 
  exit if ( $line =~ m/b\n*l\n*a\n*h/m); 
}
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He/She did not understand the scope of the request. Probably the posted request was not too clear.

I don't want to match things on a line by line only and I don't want to modify $/ to read other types of chunks of text. Just set $/= undef.

The deeper problem is how to apply a regular expression with multiple matches options to a stream so I don't have to load large pieces of the file and to re-start the reglar expression if it fails.

So far one of the suggestions makes possible sense... if the regex engine can be tricked into working with an expanding buffer.

Sergio