The link references a previous exchange similar to yours The specific case was about using the lineinfile module and with_sequence to add a parameter to all the kernel liles in grub.conf
here is a copy of what I wrote: " tasks 1: count the number of lines to replace (via shell module using and grep -E <regexp> | wc -l ) using register to remember the linecounted task 2: using lineinfile and with_sequence: linecounted one caveat is that with sequence does not accept a 0 count ( a potential future improvement ?) so just add 1 to the count (you do not care about doing it one more time) then you can run those 2 tasks multiples times works for me on grub.conf " Phil 2014-05-01 15:34 GMT+02:00 kesten broughton <kesten.brough...@gmail.com>: > Phil, the link doesn't work for me. > > > On Thursday, May 1, 2014 2:32:23 AM UTC-5, Philippe Eveque wrote: > >> In similar case A workaround I used is to add 1 to your sequence count >> see https://mail.google.com/mail/#search/label%3Aansible+with_ >> sequence/1435e13b34e3a0e1 >> >> Phil >> >> >> 2014-04-30 23:51 GMT+02:00 kesten broughton <kesten.b...@gmail.com>: >> >>> The error is >>> fatal: [localhost] => can't count backwards >>> >>> This occurs whenever count=0 or start=M end=M >>> >>> If with_sequence is used for the purpose of bringing a system to a state >>> = HAS N of something >>> then there should be a way of running the playbook twice and not having >>> anything new created. >>> That's what i meant by idempotent. >>> >>> "with sequence can't traverse a zero length list" accurately describes >>> my concern >>> >>> kesten >>> >>> On Wednesday, April 30, 2014 3:03:56 PM UTC-5, Michael DeHaan wrote: >>> >>>> You are throwing two words together that have nothing to do with each >>>> other. >>>> >>>> with_sequence is a loop. >>>> >>>> Idempotency is a mathematical statement that says "F(X) = F(F(X))" for >>>> how many times X is applied. >>>> >>>> "This will work if M is strictly less than N, but if M=N (the >>>> idempotent case) then ansible gives an error." >>>> >>>> What you have here is Ansible giving an error. It has nothing to do >>>> with idempotency. >>>> >>>> It may imply "with sequence can't traverse a zero length list", which >>>> more accurately describes the problem. >>>> >>>> So, the best thing to do here is to share what the error is and we can >>>> go from there. >>>> >>>> >>>> >>>> >>>> >>>> >>>> On Wed, Apr 30, 2014 at 9:34 AM, Kesten Broughton < >>>> solarmobi...@gmail.com> wrote: >>>> >>>>> >>>>> I recently had a need for with_sequence, but it doesn't seem possible >>>>> to do a zero count of actions. >>>>> >>>>> Suppose i have a local action to create N things, perhaps vms or >>>>> floating ips. Some number M < N may already be present. >>>>> >>>>> I'd like to do >>>>> >>>>> hosts: localhost >>>>> vars: >>>>> expected_foo_count: 10 >>>>> >>>>> - name: Get the number of foos >>>>> shell: echo M >>>>> register: foo_count >>>>> >>>>> - name: Create the missing number of foos >>>>> shell: make_new_foos >>>>> with_sequence: start=0 end="{{expected_foo_count -foo_count.stdout >>>>> }}" >>>>> >>>>> or with_sequence: count="{{expected_foo_count - foo_count.stdout}}" >>>>> >>>>> This will work if M is strictly less than N, but if M=N (the >>>>> idempotent case) then ansible gives an error. >>>>> >>>>> fatal: [localhost] => can't count backwards >>>>> I tried putting a "when" guard such as >>>>> when: "{{ expected_foo_count - foo_count.stdout > 0 }}" >>>>> >>>>> But it appears "when" gets evaluated after the with_sequence >>>>> conditional. That in itself poses problems, since in branching code the >>>>> register variables may not be defined and you have to litter code with >>>>> when: "{{ (register_var or '') | conditional }}". >>>>> >>>>> The problem with the with_sequence is in the lib/ansible/runner/lookup_ >>>>> plugins/sequence.py >>>>> >>>>> def generate_sequence(self): >>>>> numbers = xrange(self.start, self.end+1, self.stride) >>>>> >>>>> which means that contrary to conventional python such as >>>>> range(a,b) which gives a sequence starting at 'a' and ending at 'b-1', >>>>> ie. [a,b) >>>>> >>>>> with_sequence: start=n end=m >>>>> >>>>> runs over the sequence [n,m]. If n=m with_sequence still executes >>>>> once, so there is no possible way to have a with_sequence that runs zero >>>>> times. >>>>> >>>>> changing the generate_sequence code to >>>>> >>>>> def generate_sequence(self): >>>>> numbers = xrange(self.start, self.end, self.stride) >>>>> >>>>> Fixes the problem. >>>>> >>>>> Is there a design reason behind not allowing for zero count sequences? >>>>> If so, how can a playbook including with_sequence be made idempotent? >>>>> >>>>> kesten >>>>> >>>>> -- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "Ansible Project" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>> an email to ansible-proje...@googlegroups.com. >>>>> To post to this group, send email to ansible...@googlegroups.com. >>>>> >>>>> To view this discussion on the web visit https://groups.google.com/d/ >>>>> msgid/ansible-project/CAO2fFsVLwC6qoVKReu--zjyfOwUA1KUJQWy2cG3 >>>>> 6nmHRietk0g%40mail.gmail.com<https://groups.google.com/d/msgid/ansible-project/CAO2fFsVLwC6qoVKReu--zjyfOwUA1KUJQWy2cG36nmHRietk0g%40mail.gmail.com?utm_medium=email&utm_source=footer> >>>>> . >>>>> For more options, visit https://groups.google.com/d/optout. >>>>> >>>> >>>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Ansible Project" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to ansible-proje...@googlegroups.com. >>> To post to this group, send email to ansible...@googlegroups.com. >>> To view this discussion on the web visit https://groups.google.com/d/ >>> msgid/ansible-project/263df645-0b20-419b-ae3f- >>> 2cdff75280f5%40googlegroups.com<https://groups.google.com/d/msgid/ansible-project/263df645-0b20-419b-ae3f-2cdff75280f5%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> -- > You received this message because you are subscribed to the Google Groups > "Ansible Project" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to ansible-project+unsubscr...@googlegroups.com. > To post to this group, send email to ansible-project@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/ansible-project/361bfbdc-5ba1-4bcc-bde5-603c633cf4fa%40googlegroups.com<https://groups.google.com/d/msgid/ansible-project/361bfbdc-5ba1-4bcc-bde5-603c633cf4fa%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "Ansible Project" group. To unsubscribe from this group and stop receiving emails from it, send an email to ansible-project+unsubscr...@googlegroups.com. To post to this group, send email to ansible-project@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/ansible-project/CAB1FMuSeAVaMDXKUfNRPz6pphRKNE8LV-PaXhqUGhK92ORTX8A%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
