Execute the specified command after a connection has been established. The command must be specified as a full pathname. All input from the remote client will be sent to the application and responses sent back to the remote client over the socket, thus making your command-line application interactive over a socket. Combined with --keep-open, Ncat will handle multiple simultaneous connections to your specified port/application like inetd. Ncat will only accept a maximum, definable, number of simultaneous connections controlled by the -m option. By default this is set to 100.

Same as -e, except it tries to execute the command via /bin/sh. This means you don't have to specify the full path for the command, and shell facilities like environment variables are available.