Live and learn.
ping 127.1
PING 127.1 (127.0.0.1): 56 data bytes
64 bytes from 127.0.0.1: icmp_seq=0 ttl=64 time=0.151 ms
64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.209 ms
Zero octets can be shortened as long as it doesn’t change the meaning. For example, in the case of 127.0.0.1, the first octet (127) is always mandatory, and the zero octets can be shortened as follows:
127.1 — this is a valid shorthand for 127.0.0.1.
So, the command ping 127.1 is essentially equivalent to ping 127.0.0.1