There's nothing in my code that violates strict, so I don't know why that would presumably be a problem. Try

perl -Mstrict -wne'print "$1\n" while /\B(-I\S+)/g;' infile which is the same as

#!/usr/bin/perl -w
use strict;
while(<>) {
    print "$1\n" while /\B(-I\S+)/g;
}
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As a minor point, you preferrably want to split on \s+.

Makeshifts last the longest.