use warnings;
use strict;

...

while (<DATA>) {
    ...
}

...

__DATA__
285 blabla_data[28] OUTPUT (
286 REQUIRED (
287 lead_up 0.193118 br fclk clkdom(3)
288 early_lea clkdom(3)
289 late_trail_dn -0.084738 br fclk clkdom(3)
290 late_tra
291 )
292 cext %0.00151055
299 min_ceff_up %0.034
300 TEXT TO BE REMOVED
301 )
302 blabla5 [145] OUTPUT (
303 REQUIRED (
304 early qclk clkdom(6)
305 early_l qclk clkdom(7)
306 late_trail_dn -0.125163 bf qclk clkdom(7)
307 late_t(7)
308 TEXT TO BE REMOVED
309 )