bash - 为什么将 `trap -` 放入函数中时不起作用？

Question

精简版

在 Bash 脚本中，我激活了一个陷阱，然后通过调用 trap - EXIT ERR SIGHUP SIGINT SIGTERM 停用它。 .当我直接在脚本中进行停用时，它可以工作。但是，当我将完全相同的代码行放在 Bash 函数中时，它会被忽略，即，如果稍后命令返回不同于零的退出代码，则陷阱仍会被激活。为什么？

长版

我有一堆函数可以处理陷阱:

trap_stop()
{
    echo "trap_stop"
    trap - EXIT ERR SIGHUP SIGINT SIGTERM
}

trap_terminate()
{
    local exitCode="$?"
    echo "trap_terminate"
    trap_stop

    local file="${BASH_SOURCE[1]}"
    local stack=$(caller)
    local line="${stack% *}"

    if [ $exitCode == 0 ]; then
        echo "Finished."
    else
        echo "The initialization failed with code $exitCode in $file:${line}."
    fi

    exit $exitCode
}

trap_start()
{
    echo "trap_start"
    trap "trap_terminate $LINENO" EXIT ERR SIGHUP SIGINT SIGTERM
}

像这样使用时:

trap_start  # <- Trap started.

echo "Stopping traps."
trap_stop  # <- Trap stopped before calling a command which exits with exit code 2.

echo "Performing a command which will fail."
ls /tmp/missing
exit_code="$?"

echo "The result of the check is $exit_code."

我得到以下输出:

trap_startStopping traps.trap_stopPerforming a command which will fail.ls: cannot access '/tmp/missing': No such file or directorytrap_terminatetrap_stopThe initialization failed with code 2 in ./init:41.

Despite the fact that function deactivating the trap was called, the trap was still triggered when calling ls on a directory which doesn't exist.

On the other hand, when I replace the call to trap_stop by the actual trap - statement, like this:

trap_start

echo "Stopping traps."
trap - EXIT ERR SIGHUP SIGINT SIGTERM  # <- This statement replaced the call to `trap_stop`.

echo "Performing a command which will fail."
ls /tmp/missing
exit_code="$?"

echo "The result of the check is $exit_code."

那么输出是正确的，即陷阱没有被激活，我到达了脚本的末尾。

陷阱_开始
停止陷阱。
执行将失败的命令。
ls: 无法访问 '/tmp/missing': 没有那个文件或目录
检查结果为 2。

为什么要搬家 trap -到一个函数使它停止工作？

Answer 1

编辑 (@KamilCuk 提供):如果您的 bash 版本低于 4.4，请升级您的 bash，它可以解决问题。

我在你的代码中添加了一些调试:

echo "Stopping traps."
trap -p
trap_stop  # <- Trap stopped before calling a command which exits with exit code 2.
trap -p

并得到:

Stopping traps.
trap -- 'trap_terminate 29' EXIT
trap -- 'trap_terminate 29' SIGHUP
trap -- 'trap_terminate 29' SIGINT
trap -- '' SIGFPE
trap -- 'trap_terminate 29' SIGTERM
trap -- '' SIGXFSZ
trap -- '' SIGPWR
trap -- 'trap_terminate 29' ERR
trap_stop
trap -- '' SIGFPE
trap -- '' SIGXFSZ
trap -- '' SIGPWR
trap -- 'trap_terminate 29' ERR

如您所见， trap -部分确实有效，除了 ERR健康)状况。

经过一些手册页时间:

echo "Stopping traps."
set -E
trap_stop  # <- Trap stopped before calling a command which exits with exit code 2.

产量:

trap_start
Stopping traps.
trap_stop
Performing a command which will fail.
ls: cannot access '/tmp/missing': No such file or directory
The result of the check is 2.

bash(1) 的相关部分:

-E If set, any trap on ERR is inherited by shell functions, command substitutions, and commands executed in a subshell environment. The ERR trap is normally not inherited in such cases.

也就是说，这似乎是 bash 中的一个错误:

#!/bin/bash

t1()
{
    trap 'echo t1' ERR
}

t2()
{
    trap 'echo t2' ERR
}

t1
false
t2
false

产量:

t1
t1

而我至少期望:

t1
t2