(1) Execute方法
$irb
>> exec 'echo "hello $HOMENAME"'
(2) System方法
>>system 'echo "hello $HOMENAME"'
(3) 反引号
>> today= `date`
(4) open3#popen3
>>stdin,stdout,stderr=open3.popen3('dc')
(5) IO#popen
>>IO.popen("date") {|f| puts f.gets}
(6) open#popen4
>> require "open4"
=>true
>>pid,stdin,stdout,stderr=open4::popen4 "false"
