How to filter shell output to only number with decimal?

Question

I have CI/CD Config which required python version to be set to default by pyenv. I want to python2 -V output showed up with only, example, 2.7.18. But, rather than showing 2.7.18, it showing full text Python 2.7.18 .

But, when I use it in python3 python -V , it showed the correct & current python3 version ( 3.9.0 ).

I use this code to try showing numbers only: $(python -V | grep -Eo '[0-9]\.[0-9]\.[10-19]') .

And to set default with pyenv: pyenv global $(python3 -V | grep -Eo '[0-9]\.[0-9]\.[10-19]') $(python -V | grep -Eo '[0-9]\.[0-9]\.[10-19]')

So pyenv $(python3 version) $(python2 version)

Here is the image:

Image of wrong output

Thanks!

Answer 1

A simple way would be to just replace the string Python with the emtpy string, if it exists.

Here a quick one-liner

python -V 2>&1| sed -e "s/Python//g" | xargs

That would print the python version, redirects stderr to stdout, replaces "Python" with "". Xargs without parameters returns the trimmed input string.

Answer 2

Here are a few more ways to get the version number:

# Print 1 word per line, the select the last word:
python -V 2>&1 | xargs -n1 | tail -n1

# Print the last word:
python -V 2>&1 | perl -lane 'print $F[-1];'

# Print the first stretch of 1 or more { digits or periods }:
python -V 2>&1 | grep -Po '[\d.]+'