io - How to use Bash read with a timeout?

Question

I can ask the user to press Enter by using read, and have him wait by calling sleep. But I?can’t think of a way of doing both at the same time. I?would like the user to be given the choice:

Press Ctrl+C to Cancel, Enter?to continue or just wait 10?seconds

How can I?do that?

Answer 1

In bash, read has a -t option where you can specify a timeout. From the manpage:

read [-ers] [-u fd] [-t timeout] [-a aname] [-p prompt] [-n nchars] [-d delim] [name ...]

-t timeout: cause read to time out and return failure if a complete line of input is not read within timeout seconds. This option has no effect if read is not reading input from the terminal or a pipe.

Transcript below (without hitting ENTER):

$ date ; read -t 10 -p "Hit ENTER or wait ten seconds" ; echo ; date
Tue Feb 28 22:29:15 WAST 2012
Hit ENTER or wait ten seconds
Tue Feb 28 22:29:25 WAST 2012

Another, hitting ENTER after a couple of seconds:

$ date ; read -t 10 -p "Hit ENTER or wait ten seconds" ; date
Tue Feb 28 22:30:17 WAST 2012
Hit ENTER or wait ten seconds
Tue Feb 28 22:30:19 WAST 2012

And another, hitting CTRL-C:

$ date ; read -t 10 -p "Hit ENTER or wait ten seconds" ; echo ; date
Tue Feb 28 22:30:29 WAST 2012
Hit ENTER or wait ten seconds