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

In shell script I am checking whether this packages are installed or not, if not installed then install it. So withing shell script:

    import nltk
    echo nltk.__version__

but it stops shell script at import line

in linux terminal tried to see in this manner:

    which nltk

which gives nothing thought it is installed.

Is there any other way to verify this package installation in shell script, if not installed, also install it.

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.