fail when a file exist in puppet - puppet

Question

I am trying to write a puppet script which will install a module by un-tar. I want puppet to fail if it is already un tar. I tried to do below code but it always fails even if directory is absent.
I am checking if /opt/sk is present then fail otherwise proceed on installation.
define splunk::fail($target)
{
$no = 'true'
case $no {
default : { notice($no) }#fail('sk is already installed.')}
}
}
define splunk::forwarder( $filename , $target )
{
file{"$target/sk":
ensure => present
}
splunk::fail{"NO":
target => '/opt/',
require => File[$target],
}
file{"$target/A.tgz":
source => $filename ,
replace => false ,
}
exec{"NO1":
command => "tar xzvf A.tgz" ,
cwd => $target ,
require => File["$target/A.tgz"] ,
}
exec{"Clean":
command => "rm -rf A.tgz" ,
cwd => target ,
require => Exec["NO1"],
}
}
splunk::forwarder {"non":
filename => 'puppet:///modules/splunk/files/NO.tgz' ,
target => '/opt/',
}
Thanks

Answer 1

Define custom_fact and use it combined with fail resource.
In your ruby directory e.g /usr/lib/ruby/vendor_ruby/facter define file tmp_exist.rb with content:
# tmp_exist.rb
Facter.add('tmp_exist') do
setcode do
File.exist? '/root/tmp'
end
end
Next use it in puppet manifest. E.g I combined it with str2bool function from stdlib:
class test {
if !str2bool($::tmp_exist) {
fail('TMP NOT EXIST')
}
if !str2bool($::foo_exist) {
fail('FOO NOT EXIST')
}
}
include test
In /root create only tmp file.
In result you will have:
Error: FOO NOT EXIST at /etc/puppet/deploy/tests/test.pp:8 on node dbmaster
UPDATED: I updated my answer. Chris Pitman was right, my previous solution works only on puppet master or with puppet apply.
I have also found an article describing how to define custom function file_exists in puppet. That also might be helpful.

Answer 2

You should use "creates" attribute of exec, for example:
exec { 'install':
command => "tar zxf ${package}",
cwd => $some_location,
path => $path,
creates => "${some_location}/my_package",
}
Puppet will only execute 'install' if "${some_location}/my_package" doesn't exist.