Feature Friday #3: execresult_as_data()

When you want to inspect both the return code and output from a command execresult_as_data() might be the function you are searching for.

Most CFEngine policy writers have used execresult() and returnszero(). They are useful when you want to do something based on the output of a command or based on its successful execution (returning zero). For example:

bundle agent __main__
{
  vars:
      "hostname" string => execresult( "$(paths.hostname)", "useshell" );

  classes:
      "my_command_returned_zero"
        expression => returnszero( "$(paths.hostname)", "noshell" );

  reports:
      "$(hostname)";

    my_command_returned_zero::
      "$(paths.hostname) returned 0";
}

cf-agent --no-lock --log-level info --file /tmp/feature-friday-3.cf

precision-5570
R: precision-5570
R: /bin/hostname returned 0

But, sometimes, you care about specific return codes. However, you might also want to consider the output from a command. execresult_as_data() facilitates inspecting both output and return code from a command’s execution, by returning a data structure. Let’s take a look.

bundle agent __main__
{
  vars:
      "i_got" data => execresult_as_data( "$(paths.hostname)", "useshell" );

  reports:
      "$(paths.hostname) emitted '$(i_got[output])' and returned '$(i_got[exit_code])'";
}

cf-agent --no-lock --log-level info --file /tmp/feature-friday-3-1.cf

R: /bin/hostname emitted 'precision-5570' and returned '0'

Happy Friday! 🎉