#### 3.5.4.13 Executing Shell Commands: ~! and ~| ¶

The ‘`~!`’ escape executes specified command and returns you to `mail` compose mode without altering your message. When used without arguments, it starts your login shell. The ‘`~|`’ escape pipes the message composed so far through the given shell command and replaces the message with the output the command produced. If the command produced no output, `mail` assumes that something went wrong and retains the old contents of your message.