#!/usr/bin/perl

our(@l,$c);
while(@l = getpwent) {
    $~ = $c++ % 2 ? 'foo' : 'bar';
    write;
}

format foo =
left @<<<<<<<<<<<< @<<<<<<<<<<<<
$l[0],$l[7]
.
format bar =
right @>>>>>>>>>>> @>>>>>>>>>>>>
$l[0],$l[7]
.