my $output = "Error: Illegal option -- x";

print "\nTRUE\n"
    if $output
    =~ /The.*?command\stakes.*?arguments;\syou\sgave.*
        |Illegal\soption.*
        |.*?is\snot\sa\svalid\soption.*/ix
[download]

It does now. :)

Embedded newlines and spaces count unless you use the x.