how to check which version of nltk, scikit learn installed?

import nltk is Python syntax, and as such won't work in a shell script.

To test the version of nltk and scikit_learn, you can write a Python script and run it. Such a script may look like

import nltk
import sklearn

print('The nltk version is {}.'.format(nltk.__version__))
print('The scikit-learn version is {}.'.format(sklearn.__version__))

# The nltk version is 3.0.0.
# The scikit-learn version is 0.15.2.

Note that not all Python packages are guaranteed to have a __version__ attribute, so for some others it may fail, but for nltk and scikit-learn at least it will work.

Try this:

$ python -c "import nltk; print nltk.__version__"

In Windows® systems you can simply try

pip3 list | findstr scikit

scikit-learn                  0.22.1

If you are on Anaconda try

conda list scikit

scikit-learn              0.22.1           py37h6288b17_0

And this can be used to find out the version of any package you have installed. For example

pip3 list | findstr numpy

numpy                         1.17.4
numpydoc                      0.9.2

Or if you want to look for more than one package at a time

pip3 list | findstr "scikit numpy"

numpy                         1.17.4
numpydoc                      0.9.2
scikit-learn                  0.22.1

Note the quote characters are required when searching for more than one word.

Take care.

For checking the version of scikit-learn in shell script, if you have pip installed, you can try this command

pip freeze | grep scikit-learn
scikit-learn==0.17.1

Hope it helps!