embedding Bash Script in python without using subprocess call

Question

I have been able to use subprocess to embed bash script into python. I happen to navigate through a python code today and stumbled across this line of code below, which also embed bash script into python - using construct analogous to docstring.

#!/bin/bash -

''''echo -n
if [[ $0 == "file" ]]; then
  ..
fi
'''

Can someone throw light on this approach. What is this approach called, and perhaps the benefits associated. I can obviously see simplicity but I think there's more to this than that.

Jeremy Roman · Accepted Answer · 2013-03-03 20:01:42Z

This is a somewhat clever way to make the file both a valid Python script and a valid bash script. Note that it does not cause a subprocess to magically be spawned. Rather, if the file is evaluated by bash, the bash script will be run, and if it is evaluated by Python, the bash script will be ignored.

It's clever, but probably not a good software engineering practice in general. It usually makes more sense to have separate scripts.

To give a more concrete example (say this file is called "polyglot"):

''''echo hello from bash
exit
'''

print('hello from python')

As you note, bash will ignore the initial quotes, and print "hello from bash", and then exit before reaching the triple quote. And Python will treat the bash script as a string, and ignore it, running the Python script below.

$ python polyglot
hello from python
$ bash polyglot
hello from bash

But naturally, this can usually (and more clearly) be refactored into two scripts, one in each language.

Karoly Horvath · Accepted Answer · 2013-03-03 19:52:38Z

3

no, that's not embedded into python, the shebang says it's a bash script
the '''' is '' twice, which is just an empty string, it doesn't have any effect.
the ''' is invalid, as the last ' is not closed.

answered Mar 3, 2013 at 19:52

Karoly Horvath

96.7k11 gold badges123 silver badges181 bronze badges

4 Comments

Jeremy Roman Over a year ago

Actually, '''' is parsed as opening a docstring, followed by a literal single quote.

Jeremy Roman Over a year ago

Yes, but the point is that the bash script can be ignored by Python. The Python parsing is the interesting bit.

Karoly Horvath Over a year ago

I understand that but in its current form this bash script has invalid syntax - unexpected EOF while looking for matching `''

Jeremy Roman Over a year ago

OP has simply omitted the "exit" statement before that, which is common in this pattern.

Collectives™ on Stack Overflow

embedding Bash Script in python without using subprocess call

2 Answers 2

Comments

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related