add possibility to override exists command.

Fixes ccin2p3#37

Author: faxm0dem

README.md

@@ -128,6 +128,19 @@ cpan {'DBD::DB2':
 }
 ```
 
+### Overriding exists code
+
+Some modules like `Sys::RunAlone` don't return a code 0 when invoked with `perl -M$MODULE_NAME -e1`.
+This means there's no way for puppet to check if they're installed or not (in an agnostic way).
+Therefore you'll have to override the method. Use the `%` sign if you need the module name in the command line.
+
+```puppet
+cpan {'Sys::RunAlone':
+  ensure => 'present',
+  exists_command => 'perl -M% -e"__END__"',
+}
+```
+
 ## Reference
 
 ## Classes

lib/puppet/provider/cpan/default.rb

@@ -46,8 +46,11 @@ def create
       system("#{umask} yes | perl #{ll} -MCPAN -e 'CPAN::install #{resource[:name]}'")
     end
 
-    #cpan doesn't always provide the right exit code, so we double check
-    system("perl #{ll} -M#{resource[:name]} -e1 > /dev/null 2>&1")
+    exists_command = "perl #{ll} -M#{resource[:name]} -e1 > /dev/null 2>&1"
+    if resource[:exists_command]
+      exists_command = resource[:exists_command].gsub(/\%/,resource[:name])
+    end
+    system(exists_command)
     estatus = $?.exitstatus
 
     if estatus != 0
@@ -88,8 +91,12 @@ def exists?
     if resource[:local_lib]
       ll = "-Mlocal::lib=#{resource[:local_lib]}"
     end
-    Puppet.debug("perl #{ll} -M#{resource[:name]} -e1 > /dev/null 2>&1")
-    output = `perl #{ll} -M#{resource[:name]} -e1 > /dev/null 2>&1`
+    exists_command = "perl #{ll} -M#{resource[:name]} -e1 > /dev/null 2>&1"
+    if resource[:exists_command]
+      exists_command = resource[:exists_command].gsub(/\%/,resource[:name])
+    end
+    Puppet.debug(exists_command)
+    output = `#{exists_command}`
     estatus = $?.exitstatus
 
     case estatus
@@ -99,7 +106,7 @@ def exists?
       Puppet.debug("#{resource[:name]} not installed")
       false
     else
-      raise Puppet::Error, "perl #{ll} -M#{resource[:name]} -e1 failed with error code #{estatus}: #{output}"
+      raise Puppet::Error, "exists_command `#{exists_command}` failed with error code #{estatus}: #{output}"
     end
   end
 

lib/puppet/type/cpan.rb

@@ -38,6 +38,13 @@
     end
   end
 
+  newparam(:exists_command) do
+    desc 'Custom command to test for module existence'
+    validate do |value|
+      raise ArgumentError, 'String expected for exists_command.' unless value.is_a?(String)
+    end
+  end
+
   newparam(:force, :boolean => true, :parent => Puppet::Parameter::Boolean) do
     desc 'Enable/Disable to force the installation of the module. Disabled by default.'
     defaultto :false

test/exists_command.pp

@@ -0,0 +1,11 @@
+#
+class { '::cpan':
+  manage_package => false,
+  manage_config  => false,
+}
+
+cpan { 'Sys::RunAlone':
+  ensure         => present,
+  exists_command => 'perl -Mlocal::lib=/tmp/cpan -M% -e"__END__"',
+  local_lib      => '/tmp/cpan',
+}