Indeed, several mechanisms for passing this stuff to programs do exactly that. Notice that they are two distinct command-line arguments to these programs, for examples:

* http://jdebp.eu./Softwares/nosh/guide/tcp-socket-listen.html

* https://cr.yp.to/ucspi-tcp/tcpserver.html

One of the principles underlying this design was, famously, "Don't parse". Don't have one string with a separator character. Have two strings that are already separate.

* http://cr.yp.to/qmail/guarantee.html