3.4.2.2. Mail Variables

3.4.2.2. Mail Variables

Since the mail program is not running all the time, there is no way for it to inform you when you get new mail; therefore the shell does this instead.^[11] The shell can't actually check for incoming mail, but it can look at your mail file periodically and determine whether the file has been modified since the last check. The variables listed in Table 3-6 let you control how this works.

Table 3-6. Mail variables

Variable	Meaning
MAIL	Name of file to check for incoming mail
MAILCHECK	How often, in seconds, to check for new mail (default 60 seconds)
MAILPATH	List of filenames, separated by colons (:), to check for incoming mail

Under the simplest scenario, you use the standard UNIX mail program, and your mail file is /usr/mail/yourname or something similar. In this case, you would just set the variable MAIL to this filename if you want your mail checked:

MAIL=/usr/mail/yourname

If your system administrator hasn't already done it for you, put a line like this in your .bash_profile.

However, some people use nonstandard mailers that use multiple mail files; MAILPATH was designed to accommodate this. bash will use the value of MAIL as the name of the file to check, unless MAILPATH is set; in which case, the shell will check each file in the MAILPATH list for new mail. You can use this mechanism to have the shell print a different message for each mail file: for each mail filename in MAILPATH, append a question mark followed by the message you want printed.

For example, let's say you have a mail system that automatically sorts your mail into files according to the username of the sender. You have mail files called /usr/mail/you/martin, /usr/mail/you/geoffm, /usr/mail/you/paulr, etc. You define your MAILPATH as follows:

MAILPATH=/usr/mail/you/martin:/usr/mail/you/geoffm:\
/usr/mail/you/paulr

If you get mail from Martin Lee, the file /usr/mail/you/martin will change. bash will notice the change within one minute and print the message:

You have new mail in /usr/mail/you/martin

If you are in the middle of running a command, the shell will wait until the command finishes (or is suspended) to print the message. To customize this further, you could define MAILPATH to be:

MAILPATH="\
/usr/mail/you/martin?You have mail from Martin.:\
/usr/mail/you/geoffm?Mail from Geoff has arrived.:\
/usr/mail/you/paulr?There is new mail from Paul."

The backslashes at the end of each line allow you to continue your command on the next line. But be careful: you can't indent subsequent lines. Now, if you get mail from Martin, the shell will print:

You have mail from Martin.

You can also use the variable $_ in the message to print the name of the current mail file. For example:

MAILPATH='/usr/mail/you?You have some new mail in $_'

When new mail arrives, this will print the line:

You have some new mail in /usr/mail/you

The ability to receive notification of mail can be switched on and off by using the mailwarn option to the shopt command.