To send a message to a user using the appropriate utility:
cat writemail #!/bin/sh # usage: writemail user message echo "$2" |{ write "$1" || mail "$1" ;}
The user types a command such as:
writemail sarah 'call me'
The message entered by the user is piped through the command { write "$1" || mail "$1" ; }.
If the the message cannot be sent to the user's terminal (they are not logged on) with the command write "$1" then the message is sent to the user by mail.