I am trying to run both Python and bash commands in a bash script. In the bash script, I want to execute some bash commands enclosed by a Python loop:
#!/bin/bash
python << END
for i in range(1000):
#execute some bash command such as echoing i
END
How can I do this?
Use subprocess, e.g.:
import subprocess
# ...
subprocess.call(["echo", i])
There is another function like subprocess.call: subprocess.check_call. It is exactly like call, just that it throws an exception if the command executed returned with a non-zero exit code. This is often feasible behaviour in scripts and utilities.
subprocess.check_output behaves the same as check_call, but returns the standard output of the program.
If you do not need shell features (such as variable expansion, wildcards, ...), never use shell=True (shell=False is the default). If you use shell=True then shell escaping is your job with these functions and they're a security hole if passed unvalidated user input.
The same is true of os.system() -- it is a frequent source of security issues. Don't use it.
os.system() provides less control than the subprocess.Popen interface -- most importantly, it provides no way to pass data out-of-band from code (or to provide a literal argv array), making it hard to avoid shell injection vulnerabilities.shell=True is the wrong thing for your subprocess.call(["echo", i], shell=True) example: The shell script that's run is just echo, with no arguments, and the i is passed as an argument to the shell that the script doesn't refer to.
Look in to the subprocess module. There is the Popen method and some wrapper functions like call.
If you need to check the output (retrieve the result string):
output = subprocess.check_output(args ....)
If you want to wait for execution to end before proceeding:
exitcode = subprocess.call(args ....)
If you need more functionality like setting environment variables, use the underlying Popen constructor:
subprocess.Popen(args ...)
Remember subprocess is the higher level module. It should replace legacy functions from OS module.
I used this when running from my IDE (PyCharm).
import subprocess
subprocess.check_call('mybashcommand', shell=True)
