my $dirpath = 'x/y/z';
my $dh = opendir $dirpath or die $!;
map ProcessFile( "$dirpath/$_" ), readdir $dh;
closedir $dh;

sub ProcessFile {
    my $SOURCEFILE = shift;
    ( -f $SOURCEFILE ) or return; # ordinary files only
    my $TARGETFILE = $SOURCEFILE . '.out';
    my $REPORTFILE = $SOURCEFILE . '.rpt';
    # ... insert OP code here
}