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pythonbashechooptparse

OptParse, whitespace and bash

I have a weird issue with bash / optparse. I need to pass string to my python script when string is defined.

I use following code:

./lol.py `if [ -n "$URL" ]; then echo -u \"$URL\"; fi`

and here is python script:

def main():
    parser = OptionParser()
    parser.add_option("-u", dest="url")
    opts, args = parser.parse_args()
    print opts.url

When I test my bash expression it appears to be working:

user@fomce02:~$ URL="http://lol.com/my project/"
user@fomce02:~$ echo `if [ -n "$URL" ]; then echo -u \"$URL\"; fi`
-u "http://lol.com/my project/"

However when I run python script with an argument

user@fomce02:~$ ./lol.py `if [ -n "$URL" ]; then echo -u "$URL"; fi`
http://lol.com/my

it truncates part of string after whitespace.

Could you explain why it is happening and how to get it work?

Solution

  • This is because the quotes you are sending to the script are literal, not syntactic. That means lol.py receives the parameters "http://lol.com/my and project/". If you want to pass the result of a command as a single parameter you have to use syntactic quotes around the code:

    ./lol.py "$(if [ -n "$URL" ]; then echo -u "$URL"; fi)"

    Also fixed the backticks - If you're using Bash it's highly recommended to use $(). Note that the quoting context is different inside and outside the command substitution, so there's no danger of the outer quotes affecting the inner quotes.