Python3 run a complex shell command with multiple intended quotations

Question

When i run from bash:

# su -c "psql -d mapping -c \"INSERT INTO mapping (ip,username) VALUES('1.2.3.4','test');\"" postgres

It works fine, but when i try from python:

subprocess.run("su -c \"psql -d mapping -c \"INSERT INTO mapping (ip,username) VALUES('1.2.3.4','test');\"\" postgres")

It fails, i have tried different quotation marks and all failing. Could you please help?

Answer 1

There are two solutions, depending on whether or not you use the shell from Python. The trivial but inefficient solution is to pass the string with shell=True and basically just add Python quoting around it.

subprocess.run(r'''su -c "psql -d mapping -c \"INSERT INTO mapping (ip,username) VALUES('1.2.3.4','test');\"" postgres''', shell=True,
    # For good measure, you should check its status
    check=True)

More efficiently and perhaps in fact more readably, you can remove the shell from the equation, and split the command into strings yourself.

subprocess.run([
        'su', '-c',
        # The argument to "su -c" should be one string
        # Because we escaped the shell, the double quotes don't need escaping
        '''psql -d mapping -c "INSERT INTO mapping (ip,username) VALUES('1.2.3.4','test');"''',
        'postgres'],
    check=True)

Notice how with shell=True the first argument is a string which gets passed to the shell, whereas without it, you pass a list of tokens directly to the OS-level exec() or (somewhat less straightforwardly on Windows) CreateProcess(). Notice also how in the first instance I used an r'...' string to avoid having Python meddle with the backslashes in the string.