Detect python version in shell script

Question

I'd like to detect if python is installed on a Linux system and if it is, which python version is installed.

How can I do it? Is there something more graceful than parsing the output of "python --version"?

Answer 1

Make below changes to do python version change

1. Open Terminal
2. cd
3. nano ~/.bashrc
4. alias python=python3 (Add this line on top of .bashrc file) or alias python=/python3.9
5. Press ctr+o (To save the file)
6. Press Enter
7. Press ctr+x (To exit the file)
8. source ~/.bashrc OR ~/.bashrc (refresh the bashrc file)

Answer 2

The below code snippets are being used by me to check the required Python version before calling the Python script. It will exit if the Python version doesn't meet the requirement.

#!/usr/bin/bash

REQUIRED_PV=3.8
/usr/bin/env python3 -V 2>/dev/null | gawk -F'[ .]' -v req_pv="${REQUIRED_PV}" '{
    cur_pv_major=int($2)
    cur_pv_minor=int($3)
    split(req_pv, tmp, ".")
    req_pv_minor=int(tmp[2])
    if (cur_pv_major == 0 || cur_pv_minor < req_pv_minor) {
        printf "MY_SCRIPT requires Python %s or greater!\n", req_pv
        exit 1
    }
}' || exit 1

/usr/bin/env python3 MY_SCRIPT "$@"

• The output of /usr/bin/env python3 -V is for example Python 3.6.8.
• The gawk will split it with the delimiter (A blank space) and .(A dot) into Python, 3, 8, and 10.
• The error message will be fired in the below cases:
  • If the major number (e.g. 3) is null, which means there's no python3 in $PATH.
  • If the minor number (e.g. 10) is lower than the required minor number.

Answer 3

If you need to check if version is at least 'some version', then I prefer solution which doesn't make assumptions about number of digits in version parts.

VERSION=$(python -V 2>&1 | cut -d\  -f 2) # python 2 prints version to stderr
VERSION=(${VERSION//./ }) # make an version parts array 
if [[ ${VERSION[0]} -lt 3 ]] || [[ ${VERSION[0]} -eq 3 && ${VERSION[1]} -lt 5 ]] ; then
    echo "Python 3.5+ needed!" 1>&2
    # fail ...
fi

This would work even with numbering like 2.12.32 or 3.12.0, etc. Inspired by this answer.

Answer 4

We first need to detect the latest available interpreter:

for i in python python{1..9}; do which $i >/dev/null && pybin=$i ;done

[[ -n $pybin ]] && echo "found $pybin" || echo "python not found"

Example output:

found python3

If we want to then do something with the version string:

v=$($pybin -V | cut -d' ' -f2)

Full string:

echo ${v}

3.8.10

Only major + minor version:

echo ${v%.*}

3.8

Only major version:

echo ${v%%.*}

3

Answer 5

This just returns 2.7, 3.6 or 3.9

python -c 'import sys; print(".".join(map(str, sys.version_info[0:2])))'

which is what you usually you need...

Answer 6

The easiest way would be:

if ! python3 --version ; then
    echo "python3 is not installed"
    exit 1
fi

# In the form major.minor.micro e.g. '3.6.8'
# The second part excludes the 'Python ' prefix 
PYTHON_VERSION=`python3 --version | awk '{print $2}'`

Answer 7

In case you need a bash script, that echoes "NoPython" if Python is not installed, and with the Python reference if it is installed, then you can use the following check_python.sh script.

• To understand how to use it in your app, I've also added my_app.sh.
• Check that it works by playing with PYTHON_MINIMUM_MAJOR and PYTHON_MINIMUM_MINOR

check_python.sh

#!/bin/bash

# Set minimum required versions
PYTHON_MINIMUM_MAJOR=3
PYTHON_MINIMUM_MINOR=6

# Get python references
PYTHON3_REF=$(which python3 | grep "/python3")
PYTHON_REF=$(which python | grep "/python")

error_msg(){
    echo "NoPython"
}

python_ref(){
    local my_ref=$1
    echo $($my_ref -c 'import platform; major, minor, patch = platform.python_version_tuple(); print(major); print(minor);')
}

# Print success_msg/error_msg according to the provided minimum required versions
check_version(){
    local major=$1
    local minor=$2
    local python_ref=$3
    [[ $major -ge $PYTHON_MINIMUM_MAJOR && $minor -ge $PYTHON_MINIMUM_MINOR ]] && echo $python_ref || error_msg
}

# Logic
if [[ ! -z $PYTHON3_REF ]]; then
    version=($(python_ref python3))
    check_version ${version[0]} ${version[1]} $PYTHON3_REF
elif [[ ! -z $PYTHON_REF ]]; then
    # Didn't find python3, let's try python
    version=($(python_ref python))
    check_version ${version[0]} ${version[1]} $PYTHON_REF
else
    # Python is not installed at all
    error_msg
fi

my_app.sh

#!/bin/bash
# Add this before your app's code
PYTHON_REF=$(source ./check_python.sh) # change path if necessary
if [[ "$PYTHON_REF" == "NoPython" ]]; then
    echo "Python3.6+ is not installed."
    exit
fi

# This is your app
# PYTHON_REF is python or python3
$PYTHON_REF -c "print('hello from python 3.6+')";

Answer 8

Adding to the long list of possible solutions, here's a similar one to the accepted answer - except this has a simple version check built into it:

python -c 'import sys; exit(1) if sys.version_info.major < 3 and sys.version_info.minor < 5 else exit(0)'

this will return 0 if python is installed and at least versions 3.5, and return 1 if:

• Python is not installed
• Python IS installed, but its version less than version 3.5

To check the value, simply compare $? (assuming bash), as seen in other questions.

Beware that this does not allow checking different versions for Python2 - as the above one-liner will throw an exception in Py2. However, since Python2 is on its way out the door, this shouldn't be a problem.

Answer 9

Yet another way to print Python version in a machine-readable way with major and minor version number only. For example, instead of "3.8.3" it will print "38", and instead of "2.7.18" it will print "27".

python -c "import sys; print(''.join(map(str, sys.version_info[:2])))"

Works for both Python 2 and 3.

Answer 10

Detection of python version 2+ or 3+ in a shell script:

# !/bin/bash
ver=$(python -c"import sys; print(sys.version_info.major)")
if [ $ver -eq 2 ]; then
    echo "python version 2"
elif [ $ver -eq 3 ]; then
    echo "python version 3"
else 
    echo "Unknown python version: $ver"
fi

Answer 11

Here is another solution using hash to verify if python is installed and sed to extract the first two major numbers of the version and compare if the minimum version is installed

if ! hash python; then
    echo "python is not installed"
    exit 1
fi

ver=$(python -V 2>&1 | sed 's/.* \([0-9]\).\([0-9]\).*/\1\2/')
if [ "$ver" -lt "27" ]; then
    echo "This script requires python 2.7 or greater"
    exit 1
fi

Answer 12

To check if ANY Python is installed (considering it's on the PATH), it's as simple as:

if which python > /dev/null 2>&1;
then
    #Python is installed
else
    #Python is not installed
fi

The > /dev/null 2>&1 part is there just to suppress output.

To get the version numbers also:

if which python > /dev/null 2>&1;
then
    #Python is installed
    python_version=`python --version 2>&1 | awk '{print $2}'`
    echo "Python version $python_version is installed."

else
    #Python is not installed
    echo "No Python executable is found."
fi

Sample output with Python 3.5 installed: "Python version 3.5.0 is installed."

Note 1: The awk '{print $2}' part will not work correctly if Python is not installed, so either use inside the check as in the sample above, or use grep as suggested by Sohrab T. Though grep -P uses Perl regexp syntax and might have some portability problems.

Note 2: python --version or python -V might not work with Python versions prior to 2.5. In this case use python -c ... as suggested in other answers.

Answer 13

You can use the platform module which is part of the standard Python library:

$ python -c 'import platform; print(platform.python_version())'
2.6.9

This module allows you to print only a part of the version string:

$ python -c 'import platform; major, minor, patch = platform.python_version_tuple(); print(major); print(minor); print(patch)'
2
6
9

Answer 14

I used Jahid's answer along with Extract version number from a string to make something written purely in shell. It also only returns a version number, and not the word "Python". If the string is empty, Python is not installed.

version=$(python -V 2>&1 | grep -Po '(?<=Python )(.+)')
if [[ -z "$version" ]]
then
    echo "No Python!" 
fi

And let's say you want to compare the version number to see if you're using an up to date version of Python, use the following to remove the periods in the version number. Then you can compare versions using integer operators like, "I want Python version greater than 2.7.0 and less than 3.0.0". Reference: ${var//Pattern/Replacement} in http://tldp.org/LDP/abs/html/parameter-substitution.html

parsedVersion=$(echo "${version//./}")
if [[ "$parsedVersion" -lt "300" && "$parsedVersion" -gt "270" ]]
then 
    echo "Valid version"
else
    echo "Invalid version"
fi

Answer 15

You can use this too:

pyv="$(python -V 2>&1)"
echo "$pyv"

Answer 16

You can use this command in bash:

PYV=`python -c "import sys;t='{v[0]}.{v[1]}'.format(v=list(sys.version_info[:2]));sys.stdout.write(t)";`
echo $PYV

Answer 17

using sys.hexversion could be useful if you want to compare version in shell script

ret=`python -c 'import sys; print("%i" % (sys.hexversion<0x03000000))'`
if [ $ret -eq 0 ]; then
    echo "we require python version <3"
else 
    echo "python version is <3"
fi

Answer 18

You could use something along the following lines:

$ python -c 'import sys; print(sys.version_info[:])'
(2, 6, 5, 'final', 0)

The tuple is documented here. You can expand the Python code above to format the version number in a manner that would suit your requirements, or indeed to perform checks on it.

You'll need to check $? in your script to handle the case where python is not found.

P.S. I am using the slightly odd syntax to ensure compatibility with both Python 2.x and 3.x.

Answer 19

python -c 'import sys; print sys.version_info'

or, human-readable:

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