TIMTOWTDI...
$line = $1 . '...' if $line =~ m[^(.{17})];
...but ctilmes method above is the right way:)
Update: Corrected (another) typo pointed out by sauoq .
Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"When I'm working on a problem, I never think about beauty. I think only how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong." -Richard Buckminster Fuller