my $pattern = qr{            # quoted regex
    HOSTNAME:                # Literal text
    \s*                      # 0 or more whitespace
    (?:\d{4}-)?              # Some devices begin with the router model
    \Q$hostname_for_regex\E  # Router hostname (grbr-rwan-x)
    \s+                      # 1 or more whitespace
    GRBR:                    # Literal text
    \s*                      # 0 or more whitespace
    \Q$dev_ref->{grbr}\E     # Just the GRBR
    }ixms;