Accessing python script return value from bash script

Question

I have a python script (called temp.py) that returns two numbers, formatted as strings and separated by whitespace. For example, the output would look like "23.3 43.6 ". I am trying to print out these values in a bash script. I can print the entire output string via echo $OUTPUT, but I get a bad substitution error when trying to print individual elements. What am I doing wrong?

#!/bin/bash OUTPUT=$(python ./scripts/temp.py) echo $OUTPUT # Prints normally "23.3 43.6 " echo ${OUTPUT[0]} # error: bad substitution! 

Answer 1

You have two problems there. First, you are using a shell that doesn't support arrays. Most likely sh or dash. My guess is that although you have a bash shebang line there, you are calling your script with sh script.sh which means it is being interpreted by whatever sh is on your system. For example, on dash (which is the default sh on Debian and Ubuntu), you get:

$ out=$(echo 23.3 43.6 ) $ echo ${out[0]} dash: 2: Bad substitution 

However, in bash, you would get:

$ out=$(echo 23.3 43.6 ) $ echo ${out[0]} 23.3 43.6 

The next issue is that even if you run this in bash, that isn't how arrays work:

$ out=$(echo 23.3 43.6 ) $ echo ${out[0]} 23.3 43.6 $ echo ${out[1]} ## prints nothing but a newline since the variable is empty $ 

To get an array in bash, you need to put the elements inside parentheses:

$ out=( $(echo 23.3 43.6 ) ) $ echo ${out[0]} 23.3 $ echo ${out[1]} 43.6