Bash – Passing paths with spaces as arguments

argumentsbashquotingshellshell-script

I am having difficulty in passing some string variables having spaces in them as arguments to a program.
For debugging and showing the arguments being passed, I created a demo Python script -: 

##### show_args.py #####

import sys

def main():
    # Display the arguments passed to the script
    print "Number of arguments =", len(sys.argv)
    for arg in sys.argv:
        print arg

if __name__ == '__main__':
    main()

Now, the script demonstrating the problem -: 

path_with_spaces="$HOME/blah blah"
arg_list="$path_with_spaces/abc $path_with_spaces/xyz"

python show_args.py $arg_list

Output -: 

Number of arguments = 5
show_args.py
/home/anmol/blah
blah/abc
/home/anmol/blah
blah/xyz

What I actually want is this -: 

path_with_spaces="$HOME/blah blah"

python show_args.py "$path_with_spaces/abc" "$path_with_spaces/xyz"

Output -: 

Number of arguments = 3
show_args.py
/home/anmol/blah blah/abc
/home/anmol/blah blah/xyz

To confirm that the problem was occurring only for paths with spaces in them, I created the following script -: 

path_without_spaces="$HOME/blah"
arg_list="$path_without_spaces/abc $path_without_spaces/xyz"

python show_args.py $arg_list

Output -: 

Number of arguments = 3
show_args.py
/home/anmol/blah/abc
/home/anmol/blah/xyz

While searching for the solutions to this problem, I encountered this answer, according to which the correct way is to put the arguments in an array variable rather than a string variable.
The script showing this new approach -: 

path_with_spaces="$HOME/blah blah"
arg_list=("$path_with_spaces/abc" "$path_with_spaces/xyz")

python show_args.py "${arg_list[@]}"

Output -: 

Number of arguments = 3
show_args.py
/home/anmol/blah blah/abc
/home/anmol/blah blah/xyz

Although, this solution is working correctly, I still want to know if there is a way with which we can accomplish the same thing using a string variable rather an array variable.

My system configuration -:

  • Ubuntu 14.04 LTS
  • Bash 4.3.11
  • Gnome Terminal 3.6.2

Best Answer

In:

path_with_spaces="$HOME/blah blah"
arg_list="$path_with_spaces/abc $path_with_spaces/xyz"

python show_args.py $arg_list

You're using a scalar/string variable and using the split+glob operator (leaving that variable unquoted) to split the content of that variable and generate the arguments to pass to python.

The split part of the split+glob operator splits on the characters stored in the $IFS special parameter.

Here, you could disable the glob part and split on a character not found in your paths. For instance, if newline is not found in the paths:

path_with_spaces="$HOME/blah blah"
arg_list="$path_with_spaces/abc
$path_with_spaces/xyz"
IFS="
"
set -f # disable glob.
python show_args.py $arg_list

You could also use shell quoting and use eval to have the shell interpret those quotes (here using bash-specific features):

printf -v arg_list '%q ' "$path_with_spaces/abc" \
                         "$path_with_spaces/xyz"

eval "python show_args.py $arg_list"
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