Python3 run a complex shell command with multiple intended quotations

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?

You are needing to pass the internal slashes to bash, so try \"INSERT......\"" postgres..... Notice the backslash-backslash -- the first one escapes the second, the third one escapes the double quote inside the double-quoted command in bash.
– mrunion
Sep 5 '18 at 19:27

still the same issue with: subprocess.call("su -c "psql -d mapping -c \"INSERT INTO mapping (ip,username) VALUES('1.2.3.4','test');\"" postgres")
– user2913139
Sep 5 '18 at 20:01

Instead of calling subprocess.run, use a "print(...)" statement to print out what is getting output. Also, you say it fails -- what error message is being displayed?
– mrunion
Sep 5 '18 at 20:03

if i run print() i got he following error: python3 search.py File "search.py", line 49 print('su -c "psql -d mapping -c \"INSERT INTO mapping (ip,username) VALUES('1.2.3.4','test');\"" postgres") ^ SyntaxError: invalid syntax
– user2913139
Sep 5 '18 at 20:06

when run from subprocess.call i got error: FileNotFoundError: [Errno 2] No such file or directory:...............
– user2913139
Sep 5 '18 at 20:07

1 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.

shell=True

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.

shell=True

exec()

CreateProcess()

r'...'

For more on this, perhaps see also my answer at stackoverflow.com/questions/4256107/…
– tripleee
Sep 6 '18 at 5:32

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