How to return multiple variables from python to bash

Question

I have a bash script that calls a python script. At first I was just returning one variable and that is fine, but now I was told to return two variables and I was wondering if there is a clean and simple way to return more than one variable.

archiveID=$(python glacier_upload.py $archive_file_name $CURRENTVAULT)

Is the call I make from bash

print archive_id['ArchiveId']
archive_id['ArchiveId']

This returns the archive id to the bash script

Normally I know you can use a return statement in python to return multiple variables, but with it just being a script that is the way I found to return a variable. I could make it a function that gets called but even then, how would I receive the multiple variables that I would be passing back?

Global

Answer 1

From your python script, output one variable per line. Then from you bash script, read one variable per line:

Python

print "foo bar"
print 5

Bash

#! /bin/bash

python main.py | while read line ; do
    echo $line
done

Final Solution:

Thanks Guillaume! You gave me a great starting point out the soultion. I am just going to post my solution here for others.

#! /bin/bash

array=()
while read line ; do
  array+=($line)
done < <(python main.py)
echo ${array[@]}

I found the rest of the solution that I needed here

Walliw

You could also say mapfile -t array < <(python main.py) -- see help mapfile from a bash prompt. – Mcelhaney

Answer 2

The safest and cleanest way to parse any input effectively in bash is to map into an array,

mapfile -t -d, <<<"$(python your_script.py)"

Now you just need to make sure you script outputs the data you want to read with the chosen delimiter, "," in my example (-d selects a delimiter, -t trims input like newlines). The quotes are non-optional to ensure the shell doesn't separate things with spaces.

If you have a tuple of things that do not contain commas, this would be enough:

print(str(your_tuple).strip('()'))

---

Below some easy ways for easy input, before I was more familiar with Bash:

My favorite way is reading straight into a list:

x=($(python3 -c "print('a','b','c')"))
echo ${x[1]}
b
echo ${x[*]}
a b c

for this reason if my_python_function returns a tuple, I would use format to make sure I just get space delimited results:

#Assuming a tuple of length 3 is returned
#Remember to quote in case of a space in a single parameter!
print('"{}" "{}" "{}"'.format(*my_python_function())

If you want this to be generic you would need to construct the format string:

res = my_python_function()
print(("{} "*len(res)).format(*res))

is one way. No need to worry about the extra space, but you could [:-1] on the format string to get rid of it.

Finally, if you are expecting multi-word arguments (i.e. a space in a single argument, you need to add quotes, and a level of indirection (I am assuming you will only be running your own, "safe", scripts):

#myfile.py
res = my_python_function()
print(('"{}" '*len(res)).format(*res))

#my file.bash
eval x=($(python3 myfile.py))

Kautz

Thanks for sharing another way :) – Global