(my $var1 = <<EOT) =~ s/\r?\n/(munched)/g;
First line of "var1"
Second line of "var1" has a newline here ->
EOT

(my $var2 = <<EOT) =~ s/\r?\n\Z/(munched)/;
First line of "var2"
Second line of "var2" had a newline here ->
EOT