Sample .mailcap File:

application/x-client1;	 client1 < %s
application/x-client2;	 client2 %s

Here, the MIME type application/x-client1 is bound to the shell command client1, which will have data piped to its standard input. The application/x-client2 MIME type is bound to the shell command client2 with the file name containing the data passed as its only command-line argument.