use strict;
use warnings;

my $foo = "blabla foo \n yadayada \n bar bla bla";
print "\n<--\n$foo\n-->\n";

$foo =~ s/foo.+bar//s;
print "\n<--\n$foo\n-->\n";
__END__
Output:

<--
blabla foo 
 yadayada 
 bar bla bla
-->

<--
blabla  bla bla
-->