\eric, "|vacation eric"
which would send messages to you (assuming your login name was eric) and send a message back to the sender.
Vacation expects a file .vacation.msg in your home directory containing a message to be sent back to each sender. It should be an entire message (including headers). For example, it might say:
From: eric@ucbmonet.Berkeley.EDU (Eric Allman)
Subject: I am on vacation
Delivered-By-The-Graces-Of: the Vacation program
I am on vacation until July 22. If you have something urgent,
please contact Joe Kalash <kalash@ucbingres.Berkeley.EDU>.
--eric
This message will only be sent once a week to each unique sender. The people who have sent you messages are kept in the files .vacation.pag and .vacation.dir in your home directory. The -I option initializes these files, and should be executed before you modify your .forward file.
If the -I flag is not specified, vacation reads the first line from the standard input for a UNIX-style ``From'' line to determine the sender. If this is not present, a nasty diagnostic is produced. Sendmail(8) includes the ``From'' line automatically.
No message is sent if the initial ``From'' line includes the string ``-REQUEST@'' or if a ``Precedence: bulk'' or ``Precedence: junk'' line is included in the header.