Bash for循环在列表中批量

Question

I am trying to bash script where it executes following java jar command in batch mode on the basis of size of list.

i have a list of string with 54 states of USA.

list = [USA+CA,USA+TX,USA+TN...]

i need to execute following command in parallel with 4 instances having 4 values as input from list.

java -jar test-execute.jar --localities=USA+TX,USA+CA,USA+TN,USA+AB

wait till execution is complete for any instance, then start new instance of jar with next 4 states.

array=( USA+TX,USA+CA,USA+TN,USA+AB )
for i in "${array[@]}"
do
    java -jar test-execute.jar --localities= ???
done

I am not able to understand how can i dynamically provide inputs from array into jar execution.

so,

i have list of size 54,

i need to run 4 java instances in parallel with each instance having 4 unique state as input from list of 54. , once these instances complete, then start next 4 instances with next unique 4 states per instance.

update:

i have list of 54 states, 16 core machine. each java jar instance will use 4 cores, so i can run 4 java instances at a time to to use 16 core machine.

16 core machine 
   java instance-1 4 states
   java instance-2 4 states
   java instance-3 4 states
   java instance-4 4 states
 
wait till any of these instances complete, once completed, start new instance with next 4 states until all 54 states has been executed. 

please help.

Answer 1

First of all, bash array must be assigned as a space separated list as:

array=("USA+AL" "USA+AK" "USA+AZ" "USA+AR" "USA+AS" "USA+CA" ...)

Then would you please try something like:

array=("USA+AL" "USA+AK" "USA+AZ" "USA+AR" "USA+AS" "USA+CA" ...)
for (( i = 0; i < ${#array[@]}; i+=4 )); do
    echo java -jar test-execute.jar --localities="$(IFS=,; echo "${array[*]:i:4}")"
done

• The for loop has a C-like syntax to increment the index by value 4.
• The array slice ${array[*]:i:4} divides the array into sub-arrays of every four elements starting with i'th index. The last chunk with two elements are treated as well.
• $(IFS=,; echo "${array[*]:i:4}") joins the array with commas to be fed to java as an argument.

If the output looks good, drop echo in front of java .

[Edit]
As for the parallelism, we can make use of -P option to xargs . Would you please try:

array=("USA+AL" "USA+AK" "USA+AZ" "USA+AR" "USA+AS" "USA+CA" ...)
for (( i = 0; i < ${#array[@]}; i+=4 )); do
    printf "%s\n" "$(IFS=,; echo "${array[*]:i:4}")"
done | xargs -P4 -L1 -I{} java -jar test-execute.jar --localities="{}"

• It groups four states into an argument.
• The -P4 option generates four processes at a time.
• Then 16 states are processed in total at once.