Change default CLI behavior to newline separated output

[mwaxmonsky]

The current default implementation of ccpp_datafile.py outputs a comma separated list of elements:
elem1,elem2,elem3,.... This is fine for small lists but the tests are having to concatenate large lists of strings to compare the output:

required_vars_var_compatibility="ccpp_error_code,ccpp_error_message"
required_vars_var_compatibility="${required_vars_var_compatibility},cloud_graupel_number_concentration"
required_vars_var_compatibility="${required_vars_var_compatibility},cloud_ice_number_concentration"
required_vars_var_compatibility="${required_vars_var_compatibility},effective_radius_of_stratiform_cloud_graupel"
required_vars_var_compatibility="${required_vars_var_compatibility},effective_radius_of_stratiform_cloud_ice_particle"
required_vars_var_compatibility="${required_vars_var_compatibility},effective_radius_of_stratiform_cloud_liquid_water_particle"
required_vars_var_compatibility="${required_vars_var_compatibility},effective_radius_of_stratiform_cloud_rain_particle"
required_vars_var_compatibility="${required_vars_var_compatibility},effective_radius_of_stratiform_cloud_snow_particle"
required_vars_var_compatibility="${required_vars_var_compatibility},flag_indicating_cloud_microphysics_has_graupel"
required_vars_var_compatibility="${required_vars_var_compatibility},flag_indicating_cloud_microphysics_has_ice"
required_vars_var_compatibility="${required_vars_var_compatibility},horizontal_dimension"
required_vars_var_compatibility="${required_vars_var_compatibility},horizontal_loop_begin"
required_vars_var_compatibility="${required_vars_var_compatibility},horizontal_loop_end"
required_vars_var_compatibility="${required_vars_var_compatibility},num_subcycles_for_effr"
required_vars_var_compatibility="${required_vars_var_compatibility},scalar_variable_for_testing"
required_vars_var_compatibility="${required_vars_var_compatibility},scalar_variable_for_testing_a"
required_vars_var_compatibility="${required_vars_var_compatibility},scalar_variable_for_testing_b"
required_vars_var_compatibility="${required_vars_var_compatibility},scalar_variable_for_testing_c"
required_vars_var_compatibility="${required_vars_var_compatibility},scheme_order_in_suite"
required_vars_var_compatibility="${required_vars_var_compatibility},vertical_layer_dimension"

if [ "${required_vars_var_compatibility}" != "${expected}" ]; then

I wanted to get an idea from the interested parties if this is required or actively being used outside of the tests at this point?

In terms of a CLI, this goes against other similar CLI's (ls, grep, find, etc.) as it requires the user to manually separate the resulting string to do further comparisons via sed, awk, etc. And the current test interface in python is further complicated because it is doing a set comparison anyway after separating the string.

Would there be any issues if we defaulted to a newline separated output instead of a , separated string output?

[gold2718]

No objections here. It is easy to change back to a comma if that is what you need (--separator=',') and I agree that a newline default makes sense. This will require lots of changes to the run scripts but at least the change to ccpp_datafile.py should be straightforward :)
It would be nice to have a test that --separator=',' actually works

[mwaxmonsky]

Thanks @gold2718 !

Yup, we can definitely have a test that verifies the separator flag actually works. And the test changes will be trivial to implement in the unit test branch. I just won't be able to fix users calling this directly and expecting the comma separated output.