###specific tools for self-use
for distribute deployment use,
usage `allssh -f hostname_file "cmd"`
or `allscp -f hostname_file src_file dst`
a simple cmdline calculater, add to path first, set `chmod +x calc`,
usage `calc "1+2**5"`
get random lines from a huge stdin input,
usage `cat huge_file.txt|python randline.py 100`
or `randline 100 huge_file.txt`
stdin_reader: cluster stdin inputs by key, for mapreduce uses
key files set operators, support set union/difference operators ets.