bash: do different actions depending on python version installed

Question

I have to install different modules according to the version of Python installed on a machine.

A previous question asked how to do this, but it only prints the result to screen. For instance:

$ python -c 'import sys; print sys.version_info'
sys.version_info(major=2, minor=7, micro=3, releaselevel='final', serial=0)

or rather:

$ python -c 'import sys; print(".".join(map(str, sys.version_info[:3])))'
2.7.3

On a Bash shell, how can I "catch" the printed line above so that I can incorporate its value in an if-statement?

EDIT: OK, now I realize it was very simple. I got stuck initially with:

a=$(python --version)

... because it didn't assign anything to the variable a, it only printed the version to screen.

`python --version` outputs to `STDERR` due to which _it only printed the version to screen_. — devnull, Jan 21 '14 at 13:21

Stefano Sanfilippo · Answer 1 · 2014-01-21T13:21:59.017

3

You can assign the value to a variable:

pyver=$(python -c 'import sys; print(".".join(map(str, sys.version_info[:3])))')

please, note that there are no spaces around the =.

Now, you can use it in your if statement:

if [[ "$pyver" == "2.7.0" ]]; then
    echo "Python 2.7.0 detected"
fi

edited Jan 21 '14 at 13:21

answered Jan 21 '14 at 13:16

score 1 · Accepted Answer · answered Jan 21 '14 at 13:16

1

Something like this:

if [[ $(python --version 2>&1) == *2\.7\.3 ]]; then
  echo "Running python 2.7.3";
  # do something here
fi

Note that python --version outputs to STDERR so you'd need to redirect it to STDOUT.

In order to assign it to a variable,

a=$(python --version 2>&1)

answered Jan 21 '14 at 13:16

devnull

ooh ok, that's what I was missing. How could I have figured it out on my own that it was printing to STDERR? Just by guessing and trying? – Ricky Robinson Jan 21 '14 at 13:24
1

@RickyRobinson When it didn't redirect the output to the variable and printed on the screen instead, you could have said `python --version 2>/dev/null` to see what happens. – devnull Jan 21 '14 at 13:25

score 1 · Answer 3 · answered Jan 21 '14 at 13:17

1

Use command substiution (`` or $()):

if [ $(python ...)  == 2.7.3 ]
then
 ...
fi

answered Jan 21 '14 at 13:17

Igor Chubin

3 Answers3