Running bash from ruby

exec

By using Kernal#exec, the ruby process is replaced by a process invoked by exec. By using exec, the command is subject to shell expansion.

exec "echo hello world" # will print hello world
exec {"myvar"=>"value"}, "echo $myvar" # passes myvar as an environment variable

??? Behind the scenes, process tree: some ruby process with PID=3 will call exec, branches into two ruby processes (PID 3 and 4). In process 3, returns 4, in process 4 returns 0. Process 4 will turn into a bash process and process 3, still ruby, will wait for the output of process 4.

system

system method calls a system program, parsing the passed string as a command. returns true or false depending on system program exit code. Uses STDIN, STDOUT, and STDERR objects of the Ruby program to automatically print. Has another side effect of changing the global var $? which is set to a Process:Status object (includes PID and exit status).

backticks

call a system program and return its output.