Or even shorter:

use strict;

my @lines=grep(/;/, <DATA>);

print pop @lines;

__DATA__
This is not the right line
This OK, it contains a ;
This is no good either
Hey, a ; in this line!
Drop this.
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It is shorter, but it uses more memory if the text file is large as it reads in all lines of the file and keeps all lines with a ';' only to print the last line.