#!/usr/bin/ruby -w
## truncat - truncate file by tailing it into itself as in bash
##   file="/var/log/mysql.log"; tail $file > $file
##   name is an abbreviation and a nod to Cory Doctorow's story of that title
##   a sequel of sorts to his novel _Down and Out in the Magic Kingdom_

require 'ftools'

## display usage help
def usage()
  p 'truncat: Truncate file by tailing it to itself. Takes one argument, so far.'
  exit()
end

## check arg count and type a little
def check_args()
  ## if argcount is not one, quit
  if ARGV.size != 1 
    p "#{ARGV.size} is not one."
    usage()
  end
  ## if arg is not a file, quit
  if ! File::exists?(ARGV[0]) 
    p "#{ARGV[0]} is not a File."
    usage()
  end
  ## if we cannot write to arg, quit
  if ! File::writeable?(ARGV[0])
    p "#{ARGV[0]} not writable as `id` right now."
    usage
  end
  ## still here? set arg
  @victim = ARGV[0]
end

def trunc(victim)
  `tail victim > @victim`
end

check_args()
trunc(@victim)
exit