Useful scripts I used (Part 1)

Reading time ~1 minute

Run bash script repeatedly.

Loop

run() {
    declare -i number=$1
    declare -i i
    declare -i pid
    declare -i interrupted=0

    trap "echo Exiting...; interrupted=1" SIGINT SIGTERM SIGQUIT
    shift

    # Turn off "monitor mode" so the shell doesn't report terminating background jobs.
    set +m

    for ((i = 0; i < number; ++i)); do
        echo "\n-- Run ${i}th time --\n"
        $@ &
        pid=$!
        wait $pid

        # If we receive one of the signals, kill it and break
        [[ $interrupted == 1 ]] && kill $pid && break
    done

    # Switch back to default behaviour
    set -m
    trap - SIGINT SIGTERM SIGQUIT
}

其实就是给日常的命令加一个 for 循环，区别在于

  • 方便调用，不需要每次单独地写同样的循环条件表达式了；
  • 捕获信号量，只要有一次终止意图就立刻 break 整个循环，这并不是默认的，没有它的话在发送 ctrl + c 的时候循环还是会自动执行（因为 SIGINT 只是被 $@ & 捕获了，for 所在的进程会无视它的结果）；
  • 有时候我想知道一个命令到底运行了多少次，通过简单的日志可以方便看出来。

基于它的变体还有另外两个方法：

retry()
{
    declare -i number=$1
    declare -i i
    declare -i pid
    declare -i interrupted=0

    trap "echo Exiting...; interrupted=1" SIGINT SIGTERM SIGQUIT
    shift

    # Turn off "monitor mode" so the shell doesn't report terminating background jobs.
    set +m

    for ((i = 0; i < number; ++i)); do
        echo "\n-- Retry ${i}th time --\n"
        $@ &
        pid=$!

        # If command succeeded, break
        wait $pid && break

        # If we receive one of the signals, kill it and break
        [[ $interrupted == 1 ]] && kill $pid && break
    done

    # Switch back to default behaviour
    set -m
    trap - SIGINT SIGTERM SIGQUIT
}

check()
{
    declare -i number=0
    declare last_output
    declare -i ret=-1
    trap "echo Exiting...; ret=1" SIGINT SIGTERM SIGQUIT

    # Turn off "monitor mode" so the shell doesn't report terminating background jobs.
    set +m

    while true; do
        declare output=$($@)
        number=$((number+1))

        # If we receive one of the signals...
        [[ $ret -ge 0 ]] && break

        if [[ $number -eq 1 ]]; then 
            echo "-- Check ${number}th time --"
        elif [[ $last_output == $output ]]; then
            echo -e "\e[1A\e[K-- Check ${number}th time --"
        else 
            echo -ne "\e[1A\e[K"
            ret=0
        fi

        last_output=$output
    done

    [[ -z $last_output ]] || echo -n $last_output

    # Switch back to default behaviour
    set -m
    trap - SIGINT SIGTERM SIGQUIT

    return $ret
}

retry 会自动执行指定命令n次，直到成功为止，它是基于上一次的命令结果是否为0来判定成功与否。

check 是在比较第一次和第 n(n>1) 次的输出内容是否有什么变化，如果有变化就终止。

Example

run 10 date

retry 100 nslookup www.google.com

check nc -vz localhost 9000
Updated on Will Han