Run shell command and get output texts

[JmyL]

Description

I would like to run shell command and get it‘s output in console like python. This could be little bit dangerous but pretty useful for me.

[mcanouil]

See:

• Is it possible to execute bash/shell scripts? #5275
• Consider adding a standalone shell engine that doesn't rely on Knitr or Jupyter #4634

Not more dangerous than running Python which has access to bash/shell.