09-27-2013
$ echo hi
--- it just prints "hi" on the screen.
if i want to send the output to a file, then i will use output redirection.
$ echo hi > test-hi
in the same, input redirection is just the same.
Input redirection can be useful if you have written a program which expects input from the terminal and you want to provide it from a file. In the following example, myprog, which was written to read standard input and write standard output, is redirected to read myin.
$ myprog < myin
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BIFF(1) BSD General Commands Manual BIFF(1)
NAME
biff -- be notified if mail arrives and who it is from
SYNOPSIS
biff [n | y | b]
DESCRIPTION
The biff utility informs the system whether you want to be notified on your terminal when mail arrives.
Affected is the first terminal associated with the standard input, standard output or standard error file descriptor, in that order. Thus,
it is possible to use the redirection facilities of a shell to toggle the notification for other terminals than the one biff runs on.
The following options are available:
n Disable notification.
y Enable header notification.
b Enable bell notification.
When header notification is enabled, the header and first few lines of the message will be printed on your terminal whenever mail arrives. A
``biff y'' command is often included in the file .login or .profile to be executed at each login.
When bell notification is enabled, only two bell characters (ASCII 07) will be printed on your terminal whenever mail arrives.
If no arguments are given, biff displays the present notification status of the terminal to the standard output.
The biff utility operates asynchronously. For synchronous notification use the MAIL variable of sh(1) or the mail variable of csh(1).
EXIT STATUS
The biff utility exits with one of the following values:
0 Notification was enabled at the time of invocation.
1 Notification was disabled at the time of invocation.
>1 An error occurred.
COMPATIBILITY
Previous versions of the biff utility affected the terminal attached to standard error without first trying the standard input or output
devices.
SEE ALSO
csh(1), mail(1), sh(1), comsat(8)
HISTORY
The biff command appeared in 4.0BSD. It was named after the dog of Heidi Stettner. He died in August 1993, at 15.
BSD
April 28, 2013 BSD