$ perl -MO=Deparse -p -i.orig -e "s/foo/bar/; ... "
BEGIN { $^I = ".orig"; }
LINE: while (defined($_ = <ARGV>)) {
    s/foo/bar/;
    die 'Unimplemented';
}
continue {
    die "-p destination: $!\n" unless print $_;
}
-e syntax OK


##</code><code>##

#!/usr/bin/perl --

use strict;
use warnings;
Main( @ARGV );
exit( 0 );
sub Main {
    RuinSomeFilesOrig(@_);
}
sub RuinSomeFilesOrig {
    local *ARGV;
    local $^I = ".orig";
    local @ARGV = @_;

    LINE: while (defined($_ = <ARGV>)) {
        s/foo/bar/;
        ...;
    }
    continue {
        die "-p destination: $!\n" unless print $_;
    }
}