Executing python script(having arguments) from shell script

Question

myfile.sh

#!/bin/bash
echo -e "\n starting python script"
python main.py arg1
echo -e "\n done"

This is not working.

Above file has given following error

starting python script
Traceback (most recent call last):
 File "main.py", line 97, in <module>
 main()
 File "main", line 80, in main
 header = "arg1: {}\n\n".format(sys.argv[1])
ValueError: zero length field name in format
done

main.py

...
...
def main():
 """ main function
 """
 header = "arg1: {}\n\n".format(sys.argv[1])
 ...
 ...
if __name__ == "__main__":
 if len(sys.argv) == 2:
 main()
 else:
 print "\n Invalid no. of arguments"
 print "\n Usage:"
 print "\n python {} <date>\n".format(sys.argv[0])
 exit(1)

Whats the correct syntax to call a python script having arguments from shell script ?

• user189: Could you please be a little more precise? Maybe with a toy example?
• enrico.bacis: Yes it is correct, what do you mean for not working? bash throws an error, python throws an error?
• user189: What is your Python version? Could we please get the python script?
• Patrick: @user189 updated question with main.py contents and my python version is 2.6.2
• FredrikHedman: Change {} --> {0}, or maybe upgrade to 2.7 if possible. So this is not problem of calling python, but a rather a problem of using the wrong syntax for the your python version.

Answer 1

Your script should work fine. Here is a toy sample:

#!/bin/bash
echo -e "\n starting python script"
python main.py arg1 arg2 arg3
echo -e "\n done"

with main.py as

#!/usr/bin/env python
from __future__ import print_function
import sys
print("In python pgm called from shell script with args:")
for i, a in enumerate(sys.argv):
 print("argument {0} is {1}".format(i, a))

The error is probably caused by the '{}'. Need to have a recent enough python version for that to work (2.7 or better to be on the safe side...). Otherwise specify the positional argument numbers.

Answer 2

Yes, this is correct. Try this for example:

main.py

import sys
print sys.argv[1]