Comparing package versions

Package version numbers are odd things. They look like decimal numbers, but they're not: a version number is often in the form 2.6.4, for example. If you need to compare one version number with another, you can't do a straightforward string comparison: 2.6.4 would be interpreted as greater than 2.6.12. And a numeric comparison won't work because they're not valid numbers.

Puppet's versioncmp function comes to the rescue. If you pass two things that look like version numbers, it will compare them and return a value indicating which is the greater:

versioncmp( A, B )

returns:

• 0 if A and B are equal

• Greater than 1 if A is higher than B

• Less than 0 if A is less than B

How to do it…

Here's an example using the versioncmp function:

1. Modify your manifests/nodes.pp file as follows:

   node 'cookbook' {
     $app_version = '1.2.2'
     $min_version = '1.2.10'
   
     if versioncmp($app_version, $min_version) >= 0 {
       notify { 'Version OK': }
     } else {
       notify { 'Upgrade needed': }
     }...