为了将此并行化…

for i in $(whatever_list) ; do
   do_something $i
done

翻译成这样…

for i in $(whatever_list) ; do echo $i ; done | ## execute in parallel...
   (
   export -f do_something ## export functions (if needed)
   export PATH ## export any variables that are required
   xargs -I{} --max-procs 0 bash -c ' ## process in batches...
      {
      echo "processing {}" ## optional
      do_something {}
      }' 
   )

If an error occurs in one process, it won't interrupt the other processes, but it will result in a non-zero exit code from the sequence as a whole. Exporting functions and variables may or may not be necessary, in any particular case. You can set --max-procs based on how much parallelism you want (0 means "all at once"). GNU Parallel offers some additional features when used in place of xargs -- but it isn't always installed by default. The for loop isn't strictly necessary in this example since echo $i is basically just regenerating the output of $(whatever_list). I just think the use of the for keyword makes it a little easier to see what is going on. Bash string handling can be confusing -- I have found that using single quotes works best for wrapping non-trivial scripts. You can easily interrupt the entire operation (using ^C or similar), unlike the the more direct approach to Bash parallelism.

下面是一个简化的工作示例……

for i in {0..5} ; do echo $i ; done |xargs -I{} --max-procs 2 bash -c '
   {
   echo sleep {}
   sleep 2s
   }'

我需要这个，但目标进程不是当前shell的子进程，在这种情况下，等待$PID不起作用。我确实找到了以下替代方案:

while [ -e /proc/$PID ]; do sleep 0.1 ; done

这依赖于procfs的存在，它可能不可用(例如Mac不提供它)。所以对于可移植性，你可以用这个代替:

while ps -p $PID >/dev/null ; do sleep 0.1 ; done

我已经尝试过了，并结合了其他例子中最好的部分。该脚本将在任何后台进程退出时执行checkpid函数，并输出退出状态而不诉诸轮询。

#!/bin/bash

set -o monitor

sleep 2 &
sleep 4 && exit 1 &
sleep 6 &

pids=`jobs -p`

checkpids() {
    for pid in $pids; do
        if kill -0 $pid 2>/dev/null; then
            echo $pid is still alive.
        elif wait $pid; then
            echo $pid exited with zero exit status.
        else
            echo $pid exited with non-zero exit status.
        fi
    done
    echo
}

trap checkpids CHLD

wait

从Bash 5.1开始，由于引入了wait -p，有了一种很好的等待和处理多个后台作业结果的新方法:

#!/usr/bin/env bash

# Spawn background jobs
for ((i=0; i < 10; i++)); do
    secs=$((RANDOM % 10)); code=$((RANDOM % 256))
    (sleep ${secs}; exit ${code}) &
    echo "Started background job (pid: $!, sleep: ${secs}, code: ${code})"
done

# Wait for background jobs, print individual results, determine overall result
result=0
while true; do
    wait -n -p pid; code=$?
    [[ -z "${pid}" ]] && break
    echo "Background job ${pid} finished with code ${code}"
    (( ${code} != 0 )) && result=1
done

# Return overall result
exit ${result}

我几乎陷入了使用jobs -p来收集pid的陷阱，如果子进程已经退出，这将不起作用，如下面的脚本所示。我选择的解决方案是简单地调用-n N次，其中N是我有孩子的数量，这是我确定知道的。

#!/usr/bin/env bash

sleeper() {
    echo "Sleeper $1"
    sleep $2
    echo "Exiting $1"
    return $3
}

start_sleepers() {
    sleeper 1 1 0 &
    sleeper 2 2 $1 &
    sleeper 3 5 0 &
    sleeper 4 6 0 &
    sleep 4
}

echo "Using jobs"
start_sleepers 1

pids=( $(jobs -p) )

echo "PIDS: ${pids[*]}"

for pid in "${pids[@]}"; do
    wait "$pid"
    echo "Exit code $?"
done

echo "Clearing other children"
wait -n; echo "Exit code $?"
wait -n; echo "Exit code $?"

echo "Waiting for N processes"
start_sleepers 2

for ignored in $(seq 1 4); do
    wait -n
    echo "Exit code $?"
done

输出:

Using jobs
Sleeper 1
Sleeper 2
Sleeper 3
Sleeper 4
Exiting 1
Exiting 2
PIDS: 56496 56497
Exiting 3
Exit code 0
Exiting 4
Exit code 0
Clearing other children
Exit code 0
Exit code 1
Waiting for N processes
Sleeper 1
Sleeper 2
Sleeper 3
Sleeper 4
Exiting 1
Exiting 2
Exit code 0
Exit code 2
Exiting 3
Exit code 0
Exiting 4
Exit code 0

这里已经有很多答案了，但我很惊讶似乎没有人建议使用数组……这就是我所做的——这可能在将来对一些人有用。

n=10 # run 10 jobs
c=0
PIDS=()

while true

    my_function_or_command &
    PID=$!
    echo "Launched job as PID=$PID"
    PIDS+=($PID)

    (( c+=1 ))

    # required to prevent any exit due to error
    # caused by additional commands run which you
    # may add when modifying this example
    true

do

    if (( c < n ))
    then
        continue
    else
        break
    fi
done 


# collect launched jobs

for pid in "${PIDS[@]}"
do
    wait $pid || echo "failed job PID=$pid"
done