Looks like your pipe is metal, but the purple color on the open end looks like plastic pipe primer. With either material and your only concern being keeping critters out, I would recommend using these plastic pipe caps and just drill a hole big enough to pass the diameter of your un-terminated cable through:
You should be able to get them easily at any big box home improvement store. If the pipe is metal, just use super glue, epoxy glue, or maybe hot glue. If the pipe is plastic, just use PVC pipe cement. I hope this helps.
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