Ansible: How to check files is changed in shell command?

- stat: path=/etc/swift/account.ring.gz get_md5=yes
  register: before

- name: write account.ring.gz file
  shell: swift-ring-builder account.builder write_ring # update account.ring.gz
    chdir=/etc/swift
  changed_when: False # without this, as long as swift-ring-builder exits with
                      # return code 0 this task would always be reported as changed

- stat: path=/etc/swift/account.ring.gz get_md5=yes
  register: after

- debug: msg='report this task as "changed" if file changed'
  changed_when: "'{{before.stat.md5}}' != '{{after.stat.md5}}'"

- debug: msg='execute this task if file changed'
  when: "'{{before.stat.md5}}' != '{{after.stat.md5}}'"

If what you really want is to report the task 'write account.ring.gz file' as changed or not changed based on outcome of swift-ring-builder then you have to run a mini shell script. Something like this (not tested):

- name: write account.ring.gz file
  shell: bfr=`md5sum account.ring.gz`; swift-ring-builder account.builder write_ring; aftr=`md5sum account.ring.gz`; test $bfr -eq $aftr
    chdir=/etc/swift

or if I remember the md5sum options correctly:

- name: write account.ring.gz file
  shell: echo `md5sum account.ring.gz` account.ring.gz > /tmp/ff; swift-ring-builder account.builder write_ring; md5sum -c /tmp/ff
    chdir=/etc/swift