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This is a more accurate way to watch the progress of a dd process. The $DDPID=$! is needed so that you don't get the PID of the sleep. The sleep 1 is needed because in my testing at least, if you run kill -USR1 against dd too quickly, it will kill it off instead of display the status. So you need to wait a second, probably so that it can configure itself to trap the USR1 signal.
Check out the usage of 'trap', you may not have seen this one much. This command provides a way to schedule commands at certain times by running them after sleep finishes sleeping. In the example 'sleep 2h' sleeps for 2 hours. What is cool about this command is that it uses the 'trap' builtin bash command to remove the SIGHUP trap that normally exits all processes started by the shell upon logout. The 'trap 1' command then restores the normal SIGHUP behaviour.
It also uses the 'nice -n 19' command which causes the sleep process to be run with minimal CPU.
Further, it runs all the commands within the 2nd parentheses in the background. This is sweet cuz you can fire off as many of these as you want. Very helpful for shell scripts.
Very useful in shell scripts because you can run a task nicely in the background using job-control and output progress until it completes.
Here's an example of how I use it in backup scripts to run gpg in the background to encrypt an archive file (which I create in this same way). $! is the process ID of the last run command, which is saved here as the variable PI, then sleeper is called with the process id of the gpg task (PI), and sleeper is also specified to output : instead of the default . every 3 seconds instead of the default 1. So a shorter version would be sleeper $!;
The wait is also used here, though it may not be needed on your system.
echo ">>> ENCRYPTING SQL BACKUP"
gpg --output archive.tgz.asc --encrypt archive.tgz 1>/dev/null &
PI=$!; sleeper $PI ":" 3; wait $PI && rm archive.tgz &>/dev/null
Previously to get around the $! not always being available, I would instead check for the existance of the process ID by checking if the directory /proc/$PID existed, but not everyone uses proc anymore. That version is currently the one at http://www.askapache.com/linux-unix/bash_profile-functions-advanced-shell.html but I plan on upgrading to this new version soon.
[Note: This command needs to be run as root].
If you are downloading something large at night, you can start wget as a normal user and issue the above command as root. When the download is done, the computer will automatically go to sleep. If at any time you feel the computer should not go to sleep automatically(like if you find the download still continuing in the morning), just create an empty file called nosleep in /tmp directory.
Ummmm.. Saw that gem on some dead-head hippies VW bus at phish this summer.. It's actually one of my favorite ways of using bash, very clean. It shows what you can do with the cool advanced features like job control, redirection, combining commands that don't wait for each other, and the thing I like the most is the use of the ( ) to make this process heirarchy below, which comes in very handy when using fifos for adding optimization to your scripts or commands with similar acrobatics.
F UID PID PPID WCHAN RSS PSR CMD
1 gplovr 30667 1 wait 1324 1 -bash
0 gplovr 30672 30667 - 516 3 \_ sleep 3
1 gplovr 30669 1 wait 1324 1 -bash
0 gplovr 30673 30669 - 516 0 \_ sleep 5
1 gplovr 30671 1 wait 1324 1 -bash
0 gplovr 30674 30671 - 516 1 \_ sleep 7
Schedule your Mac to sleep at any future time.
Also wake, poweron, shutdown, wakeorpoweron. Or repeating with
sudo pmset repeat wakeorpoweron MTWRFSU 7:00:00
pmset -g sched