Is there a way to get the value of a variable from a bash line of code?

[aborruso]

Hi,
using this

a=!for i in {1..3};do\
  echo "$i";\
done

print(a)

I get the a list ['1', '2', '3'].

Is there a way to get the i value and print it in python at the end of the loop?

Something like (that I know, it does not work):

!for i in {1..3};do\
  echo "$i";\
done

print(i)

A way to do it, is to split in two cells and use %%bash --out. Is there no way to write in a single cell long bash code and get a variable value to use it in some python code?

Thank you

[drmrd]

The short answer is "no". IPython (and Jupyter Notebooks by extension) have no direct connection to the variables you're using in an external programming language called via a magic (like %%bash).

When you assigned to a the value of ![for loop] in your first example, it was populated with the list of lines printed to stdout during the execution of [for loop]. IPython is not tracking the value of the bash variable i during this process (nor to my knowledge would there be any way to do so reliably across systems).

Likewise, when you write --out i on a cell magic like in your screenshot, you are assigning the content echoed to stdout in your for loop to a new Python variable i (in this case as a multi-line string instead of a list). The fact that i was also the variable you used in your bash script is coincidental; IPython is not introspecting into the bash process to track the value of i. If you replace --out i with --out anything and the subsequent print(i) call with print(anything), your notebook will function identically.

As to your last question about how to retrieve output from a bash script in one cell via Jupyter/IPython wizardry, your a = [for loop] approach is the most straightforward that I've used. It should also be clear from the above statements that getting a list of stdout or stderr lines (rather than a specific variable value from the bash script) is as good as you're likely to get from a magic command.

Further Reading

• The definition of the --out parameter in the script magic module.
• The shebang method of ScriptMagics that actually executes %%bash (and similar) magic cells.