How to check if string is part of command "python --version" in bash?

Question

In bash, I wish to check whether Python 2.7 is installed. While searching SO I found this: How do I test (in one line) if command output contains a certain string?

In bash, I have this:

python --version
Python 2.7.11

And so I tried this:

[[ $(python --version) =~ "2.7" ]] || echo "I don't have 2.7"
Python 2.7.11
I don't have 2.7

...which I found strange, as I expected that to work.

I also tried this:

if [[ $(python --version) =~ *2.7* ]]
    then
        echo "I have 2.7"
    else
        echo "I don't have 2.7"
fi

...which resulted in:

Python 2.7.11
I don't have 2.7

Hm! What am I doing wrong?

SLePort · Accepted Answer · 2016-10-10 17:13:10Z

1

python --version command outputs to stderr.

You can redirect stderr to stdout prior to test:

if [[ $(python --version 2>&1) =~ 2\.7 ]]
    then
        echo "I have 2.7"
    else
        echo "I don't have 2.7"
fi

edited Oct 10, 2016 at 17:13

answered Oct 10, 2016 at 5:47

SLePort

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Zulu · Accepted Answer · 2016-12-16 09:13:17Z

1

You can do it the following way. You can first check if python is installed from the which command and then capture the output of python --version

if which python > /dev/null 2>&1;
then
    if [[ $(python --version 2>&1) == *2\.7\.11 ]]; then
       echo "Python version 2.7.11 is installed."
    fi 
else
    echo "No Python executable is found."
fi

edited Dec 16, 2016 at 9:13

Zulu

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answered Oct 10, 2016 at 5:47

Inian

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