$ cat 2
1
2
3
4

$ perl -i.orig -p -l -e "print 'three' if /3/" 2

$ cat 2
1
2
three
3
4

$ cat 2.orig
1
2
3
4

$ perl -MO=Deparse -i.orig -p -l -e "print 'three' if /3/"
BEGIN { $^I = ".orig"; }
BEGIN { $/ = "\n"; $\ = "\n"; }
LINE: while (defined($_ = <ARGV>)) {
    chomp $_;
    print 'three' if /3/;
}
continue {
    print $_;
}
-e syntax OK