arrange process snapshot in a tree

tree.rb

#!/usr/bin/ruby
groups = {}
STDIN.each_line do |line|
    items = line.split
    pid = items[ARGV[0].to_i]
    ppid = items[ARGV[1].to_i]
    groups[ppid] = [] if groups[ppid].nil?
    groups[ppid] << [pid, line]
end
def print_tree groups, cmd, ppid, tab = ""
    print "#{tab}+ #{ppid} #{cmd.split.last}\n"
    groups[ppid].each do |pid, line|
        print_tree groups, line, pid, (tab + "  ")
    end if not groups[ppid].nil?
end
print_tree groups, 'init', '1'