/usr/bin/unixcat is in ucspi-unix 0.36-4.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 | #!/bin/sh
# WARNING: This file was auto-generated. Do not edit!
exec unixclient "$1" sh -c 'exec cat <&6'
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