问从命令列表中调用shell命令，直到所有命令都完成为止

EN

#!/bin/bash

max_nb_jobs=4
commands_file=$1

while IFS= read -r line; do
   while :; do
      mapfile -t jobs < <(jobs -pr)
      ((${#jobs[@]}<max_nb_jobs)) && break
      wait -n
   done
   eval "$line"
done < "$commands_file"

wait

#!/bin/bash

set -m

max_nb_jobs=4
file_list=$1

sleep_jobs() {
   # This function sleeps until there are less than $1 jobs running
   # Make sure that you have set -m before using this function!
   local n=$1 jobs
   while mapfile -t jobs < <(jobs -pr) && ((${#jobs[@]}>=n)); do
      coproc read
      trap "echo >&${COPROC[1]}; trap '' SIGCHLD" SIGCHLD
      wait $COPROC_PID
   done
}

while IFS= read -r line; do
   sleep_jobs $max_nb_jobs
   eval "$line"
done < "$file_list"

wait

max_procs=4
active_procs=0

for proc_num in {0..38}; do
    nohup your_cmd_here &

    # If we have more than max procs running, wait for one to finish
    if ((active_procs++ >= max_procs)); then
        wait -n
        ((active_procs--))
    fi
done

# Wait for all remaining procs to finish
wait

for i in {0..38}; do
    nohup scrapy crawl urlMonitor -a slice=$i & _pid=$!
    ((++i%4==0)) && wait $_pid
done

wait: wait [-n] [id ...]
Wait for job completion and return exit status.

Waits for each process identified by an ID, which may be a process ID or a
job specification, and reports its termination status.  If ID is not
given, waits for all currently active child processes, and the return
status is zero.  If ID is a a job specification, waits for all processes
in that job's pipeline.

If the -n option is supplied, waits for the next job to terminate and
returns its exit status.

Exit Status:
Returns the status of the last ID; fails if ID is invalid or an invalid
option is given.