I'm getting more and more used to having mapcar:

mapcar { push @{shift @_}, @_ } [\@user,\@pw,\@uid,\@gid],
  map { [ split /:/, $_ ] } <PASSWD>;

# Or, if you don't have mapcar prototyped at compile time:
mapcar( sub { push @{shift @_}, @_ }, [\@user,\@pw,\@uid,\@gid],
  map { [ split /:/, $_ ] } <PASSWD> );
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        - tye (but my friends call me "Tye")