Comments on: Scripting the parallel execution of a tedious task

Question: Scripting the parallel execution of a tedious task

pmbuko — Tue, 12 Dec 2006 12:03:01 -0800

Calling all shell script gurus! Help me write a command that performs an action on items in a list in parallel (as opposed to sequentially).

I am trying to write a command that zeroes out the data on any number of attached disks simultanously (or nearly so). I started with the basics and have written the script below that accomplishes the task sequentially. (This is in Mac OS X, bash shell):



diskutil list | grep /disk | grep -v disk0 | sed 's|/dev/||g' | \

while read DISK; do

diskutil zeroDisk $DISK

done

The first line returns a list of attached disks:
disk1
disk2
disk3
etc... all except disk0.

Nothing I care about resides on any disk but disk0, which is why it's excluded. The while loop executes the 'diskutil zerodisk' command on each item in the list. I can manually start this command on each disk and the computer will happily perform the tasks in parallel. How can I script the parallel execution of this task?

By: Good Brain

Good Brain — Tue, 12 Dec 2006 12:09:07 -0800

try either
"bg diskutil zeroDisk $DISK"
or
"diskutil zeroDisk $DISK &"

By: pmbuko

pmbuko — Tue, 12 Dec 2006 12:20:59 -0800

the & gives me an error. I should have mentioned that. It works fine outside a script, though.

By: grouse

grouse — Tue, 12 Dec 2006 12:28:30 -0800

pmbuko: What error?

Also, did you try using bg instead as Good Brain suggested?

By: pmbuko

pmbuko — Tue, 12 Dec 2006 12:31:19 -0800

on the mac, bg can be used on a job that has just been stopped, not while invoking a command.

The error I get by having the ampersand in the script is:



-bash: syntax error near unexpected token `;'

The ampersand immediately precedes the ;

By: pmbuko

pmbuko — Tue, 12 Dec 2006 12:33:36 -0800

ooops! My bad. The & works like a charm. It's the extraneous ; I added that was the problem.

By: Rhomboid

Rhomboid — Tue, 12 Dec 2006 12:39:36 -0800

You can skip the whole while/read thing also.

for D in $(diskutil list | grep /disk | grep -v disk0 | sed 's|/dev/||g'); do diskutil zeroDisk $D & done

By: pmbuko

pmbuko — Tue, 12 Dec 2006 18:29:08 -0800

gotta love unix.