@nicholsn thanks for these updates. a few suggestions for this example:

```
>>> from nipype.interfaces.fsl import Merge
>>> merger = Merge()
>>> merger.inputs.in_files = ['functional2.nii', 'functional3.nii']
>>> merger.inputs.dimension = 't'
>>> merger.cmdline
'fslmerge -t functional2_merged.nii FILL THIS`
>>> merger.inputs.tr = 2.25
>>> merger.cmdline
'fslmerge -tr FILL THIS'
```

since these examples go to the documentation we prefer the command line coming out clearly.