Get java version number from python

Question

I need to get the java version number, for example "1.5", from python (or bash).

I would use:

os.system('java -version 2>&1 | grep "java version" | cut -d "\\\"" -f 2')

But that returns 1.5.0_30

It needs to be compatible if the number changes to "1.10" for example.

I would like to use cut or grep or even sed. It should be in one line.

Answer 1

Considering an output like this:

$ java -version
java version "1.8.0_25"
Java(TM) SE Runtime Environment (build 1.8.0_25-b17)
Java HotSpot(TM) 64-Bit Server VM (build 25.25-b02, mixed mode)

You can get the version number with awk like this:

$ java -version 2>&1 | awk -F[\"_] 'NR==1{print $2}'
1.8.0

Or, if you just want the first two .-separated digits:

$ java -version 2>&1 | awk -F[\"\.] -v OFS=. 'NR==1{print $2,$3}'
1.8

Here, awk sets the field separator to either " or _ (or .), so that the line is sliced in pieces. Then, it prints the 2nd field on the first line (indicated by NR==1). By setting OFS we indicate what is the output field separator, so that saying print $2, $3 prints the 2nd field followed by the 3rd one with a . in between.

To use it in Python you need to escape properly:

>>> os.system('java -version 2>&1 | awk -F[\\\"_] \'NR==1{print $2}\'')
1.8.0
>>> os.system('java -version 2>&1 | awk -F[\\\"\.] -v OFS=. \'NR==1{print $2,$3}\'')
1.8

Answer 2

The Java runtime seems to send the version information to the stderr. You can get at this using Python's subprocess module:

>>> import subprocess
>>> version = subprocess.check_output(['java', '-version'], stderr=subprocess.STDOUT)

>>> print version
java version "1.7.0_79"
Java(TM) SE Runtime Environment (build 1.7.0_79-b15)
Java HotSpot(TM) Client VM (build 24.79-b02, mixed mode)

You can get the version out with a regex:

>>> import re
>>> pattern = '\"(\d+\.\d+).*\"'

>>> print re.search(pattern, version).groups()[0]
1.7

If you are using a pre-2.7 version of Python, see this question: subprocess.check_output() doesn't seem to exist (Python 2.6.5)

Answer 3

You could let grep handle a regular expression:

java -version 2>&1 | grep -Eow '[0-9]+\.[0-9]+' | head -1

Answer 4

You can't capture the command's output with os.system(). Instead, use subprocess.check_output():

>>> import subprocess
>>> java_version = subprocess.check_output(['java', '-version'], stderr=subprocess.STDOUT)
>>> java_version
'openjdk version "1.8.0_51"\nOpenJDK Runtime Environment (build 1.8.0_51-b16)\nOpenJDK 64-Bit Server VM (build 25.51-b03, mixed mode)\n'

Now that you can collect the command output, you can extract the version number using Python, rather than piping through other commands (which, incidentally, would require use of the less secure shell=True argument to check_output).

>>> version_number = java_version.splitlines()[0].split()[-1].strip('"')
>>> major, minor, _ = version_number.split('.')
>>> print 'Major: {}, Minor: {}'.format(major, minor)
Major: 1, Minor: 8