Semver with Bash

Question

With a bash script, I want to take action if the node version is less than a particular value.

How can I compare semver versions with Bash?

something like:

NV=$(node --version)

if [[ ${NV} < 5 ]]; then 
   # do something
fi

obvious that's not quite right

node --version output just looks like:

$ node --version
v6.9.5

How specific do you need the version? 1-7 or do the sub-version releases impact you? — Sterling Archer, Apr 11 '17 at 23:47
for the purposes of helping other users, let's do semver major + minor, but ignore patch? — Alexander Mills, Apr 11 '17 at 23:59

score 3 · Answer 1 · edited May 23 '17 at 12:32

3

you can use sort -V for comparing versions as stated in this post. a very nice oneliner.

or if you don't mind taking advantage of debian distributions (i'm assuming this premise here), you can:

$ dpkg --compare-versions $(node --version | grep -Eo "([0-9]\.)+[0-9]+") lt 5
$ echo $?
$ 1

edited May 23 '17 at 12:32

Community

1
1

answered Apr 12 '17 at 01:14

odradek

993
7
14

score 1 · Answer 2 · answered Apr 12 '17 at 02:20

If all you need to do is compare the first digit, you could do this :

nv=$(node --version)
if [[ $nv =~ ^v([0-9]+) ]] && (( ${BASH_REMATCH[1]} > 5 )) ; then 
   # do something
fi

This code uses the =~ regex matching operator to match any sequence of numbers following a leading "v", the parentheses allowing the digit sequence to be saved in a sub-expression, and then performing a numerical comparison on that saved sub-expression (found in the BASH_REMATCH array at index 1).

Please note that it is generally recommended (though not strictly required) to have variables other than environment variables be lowercase.

Semver with Bash

2 Answers2