You all know the deal : when you launch a command it (obviously) comes with all your environment variables. But when you want to cron it, none of them is present. We hence want to set some variables, but only in some cases. The "tty" command will help us do so.


You can use the tty tool to check if a script is called from the standard output :


if ! tty -s
then
    exec >/dev/null 2>&1
else
    MAIL_DEST="email@server.ext"
fi


  • The command tty returns :

 User Commands                                              tty(1)

NAME     tty - return user's terminal name

SYNOPSIS     tty [-l] [-s]

DESCRIPTION     The tty utility writes to the standard output  the  name  of
     the  terminal  that is open as standard input. The name that
     is used is equivalent to the string that would  be  returned
     by the ttyname(3C) function.

OPTIONS     The following options are supported:

     -l       Prints the synchronous line  number  to  which  the
              user's terminal is connected, if it is on an active
              synchronous line.

     -s       Inhibits printing of the terminal path name, allow-
              ing one to test just the exit status.

EXIT STATUS
     The following exit values are returned:

     0        Standard input is a terminal.

     1        Standard input is not a terminal.

     >1       An error occurred.