@arr = (1 .. 20);
foreach $i ( 0 .. $#arr ) {
  # do something
}

##</code><code>##

foreach $i ( 0 .. 19 ) {
  # do something
}

##</code><code>##

foreach $i (1 .. 20)) {
  # do something
}

##</code><code>##

foreach $i (@arr)) {
  # do something
}