There is an easier way to do what you want, using a CPAN module called Unix::PasswdFile:

use Unix::PasswdFile;

my $pw = Unix::PasswdFile->new('/etc/passwd') 
  or die 'Could not open /etc/passwd';

my %users = map { $_ => [$ps->user($_)] } $pw->users;
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This will create the %users hash without you needing to worry about the structure of the /etc/passwd file.