Shell Programming and Scripting

given an array of filenames files=(*) how can i loop over these in batches of four, or even better, work always with four files simultaneously.

i want do something with these files, always four of them simultaneously, and if one is ready the next should start.

one idea, but definitely not the best (not tested):

Code:

 
for i in $(seq 1 4 ${#files[@]})
 do
   ( do whatever with files[$i] ) &
   ( do whatever with files[$(($i+1))] ) &
   ( do whatever with files[$(($i+2))] )  &
   ( do whatever with files[$(($i+3))] )  &
   wait
 done

i think, this will do four tasks simultaneously, wait until all four are ready, and start with the next four files...

will this work?

or how can i start the next task if one of the first four is ready...

what happens if the number of filenames in the list are not evenly divisible by 4?

Try this:

Code:

cnt=1
for fname in *
do
    dosomecommand $fname &
    cnt=$(( cnt + 1  ))
    [ $(( $cnt % 4 )) -eq 0 ]  && wait
done
wait

This is a safer and more general approach. The simple answer to your last question: you would have to develop an application that ran system() calls as worker threads, with a job control thread feeding the worker threads the new jobs as they become free.

thank you jim,

i will use your solution...

that's too complicated for me...

dietmar