CDO

Dear Forum,

So far I have been using CDO mainly in shell scripts with only one individual cdo command at a time. This way I always end up with many temporary files and long scripts.
Is there a straightforward way of combining the commands mentioned above?

For example, I have yearly netcdf files of a large spatial domain on a tripolar grid.
I want to:
1) Select a reduced horizontal/meridional domain in each file
2) Select a few vertical levels in each file
3) Merge the resulting reduced domain along the temporal axis

Thank you very much in advance for any recommendations!