7

这是问题演示的最小代码：http: //pastebin.com/5TXDpSh5

#!/bin/bash
set -e
set -o pipefail

function echoTraps() {
    echo "= on start:"
    trap -p
    trap -- 'echo func-EXIT' EXIT
    echo "= after set new:"
    trap -p
    # we can ensure after script done - file '/tmp/tmp.txt' was not created
    trap -- 'echo SIG 1>/tmp/tmp.txt' SIGPIPE SIGHUP SIGINT SIGQUIT SIGTERM
}

trap -- 'echo main-EXIT1' EXIT

echo "===== subshell trap"
( echoTraps; )

echo "===== pipe trap"
echoTraps | cat

echo "===== done everything"

输出

===== subshell trap
= on start:
= after set new:
trap -- 'echo func-EXIT' EXIT
func-EXIT
===== pipe trap
= on start:
= after set new:
trap -- 'echo func-EXIT' EXIT
===== done everything
main-EXIT1

预期产出

===== subshell trap
= on start:
= after set new:
trap -- 'echo func-EXIT' EXIT
func-EXIT
===== pipe trap
= on start:
= after set new:
trap -- 'echo func-EXIT' EXIT
func-EXIT                 <---- here is the expected difference
===== done everything
main-EXIT1

注意：我测试了 OSX 10.9.2 bash (3.2.51) - 其他版本的 bash 与实际预期输出有相同的差异，如下所述

4

2 回答 2

1

确定这种行为是否符合预期的唯一方法是询问 Chet Ramey（GNU bash 维护者）。请将您的报告发送电子邮件至 bug-bash@gnu.org

您可以看到当前的行为似乎是正确的，因为它在以下位置明确处理子外壳情况：http: //git.savannah.gnu.org/cgit/bash.git/tree/execute_cmd.c#n621

/* We want to run the exit trap for forced {} subshells, and we
   want to note this before execute_in_subshell modifies the
   COMMAND struct.  Need to keep in mind that execute_in_subshell
   runs the exit trap for () subshells itself. */
/* This handles { command; } & */
s = user_subshell == 0 && command->type == cm_group && pipe_in == NO_PIPE && pipe_out == NO_PIPE && asynchronous;
/* run exit trap for : | { ...; } and { ...; } | : */
/* run exit trap for : | ( ...; ) and ( ...; ) | : */
s += user_subshell == 0 && command->type == cm_group && (pipe_in != NO_PIPE || pipe_out != NO_PIPE) && asynchronous == 0;

last_command_exit_value = execute_in_subshell (command, asynchronous, pipe_in, pipe_out, fds_to_close);
if (s)
    subshell_exit (last_command_exit_value);
else
    sh_exit (last_command_exit_value);

如您所见，显式子shell 情况作为一种特殊情况处理（命令分组也是如此）。正如 Adrian 发现的那样，由于多个错误报告，这种行为在历史上已经演变。

这是此特定功能的更改列表（在子外壳上触发 EXIT 陷阱）：

提交：http ://git.savannah.gnu.org/cgit/bash.git/commit/?id=a37d979e7b706ce9babf1306c6b370c327038eb9

+execute_cmd.c
+ - execute_command_internal: make sure to run the EXIT trap for group
+   commands anywhere in pipelines, not just at the end.  From a point
+   raised by Andreas Schwab <schwab@linux-m68k.org>

报告：https ://lists.gnu.org/archive/html/bug-bash/2013-04/msg00126.html （回复：在等待期间未触发管道子外壳中的陷阱退出）

提交：http ://git.savannah.gnu.org/cgit/bash.git/commit/?id=1a81420a36fafc5217e770e042fd39a1353a41f9

+execute_cmd.c
+ - execute_command_internal: make sure any subshell forked to run a
+   group command or user subshell at the end of a pipeline runs any
+   EXIT trap it sets.  Fixes debian bash bug 698411
+   http://bugs.debian.org/cgi-big/bugreport.cgi?bug=698411

报告：https ://bugs.debian.org/cgi-bin/bugreport.cgi?bug=698411 （EXIT 陷阱和管道和子shell）

提交：http ://git.savannah.gnu.org/cgit/bash.git/commit/?id=fd58d46e0d058aa983eea532bfd7d4c597adef54

+execute_cmd.c
+ - execute_command_internal: make sure to call subshell_exit for
+   {} group commands executed asynchronously (&).  Part of fix for
+   EXIT trap bug reported by Maarten Billemont <lhunath@lyndir.com>

报告： http: //lists.gnu.org/archive/html/bug-bash/2012-07/msg00084.html（交互式shell中的EXIT陷阱）

最近还有一个关于 EXIT 陷阱未在某些预期上下文中执行的错误报告：http: //lists.gnu.org/archive/html/bug-bash/2016-11/msg00054.html

于 2017-01-13T15:47:06.473 回答
0

这里还有一些测试用例供您娱乐：

$ cat traps.sh
#!/bin/bash

echoTraps() {
        echo "entering echoTraps()"

        printf "  traps: %s\n" "$(trap -p)"

        echo "  setting trap"
        trap -- 'echo "func-exit()"' EXIT

        printf "  traps: %s\n" "$(trap -p)"

        echo "exiting echoTraps()"
}

trap -- 'echo "main-exit()"' EXIT

echo "===== calling '( echoTraps; )'"
( echoTraps; )
echo

echo "===== calling 'echoTraps | cat'"
echoTraps | cat
echo

echo "===== calling '( echoTraps; ) | cat'"
( echoTraps; ) | cat
echo

echo "===== calling '{ echoTraps; } | cat'"
{ echoTraps; } | cat
echo

bash-4.2.25(1)

$ ./traps.sh
===== calling '( echoTraps; )'
entering echoTraps()
  traps:
  setting trap
  traps: trap -- 'echo "func-exit()"' EXIT
exiting echoTraps()
func-exit()

===== calling 'echoTraps | cat'
entering echoTraps()
  traps: trap -- 'echo "main-exit()"' EXIT
  setting trap
  traps: trap -- 'echo "func-exit()"' EXIT
exiting echoTraps()

===== calling '( echoTraps; ) | cat'
entering echoTraps()
  traps:
  setting trap
  traps: trap -- 'echo "func-exit()"' EXIT
exiting echoTraps()
func-exit()

===== calling '{ echoTraps; } | cat'
entering echoTraps()
  traps: trap -- 'echo "main-exit()"' EXIT
  setting trap
  traps: trap -- 'echo "func-exit()"' EXIT
exiting echoTraps()

main-exit()

bash-4.3.0(1)

$ bash-static-4.3.2/bin/bash-static traps.sh
===== calling '( echoTraps; )'
entering echoTraps()
  traps:
  setting trap
  traps: trap -- 'echo "func-exit()"' EXIT
exiting echoTraps()
func-exit()

===== calling 'echoTraps | cat'
entering echoTraps()
  traps: trap -- 'echo "main-exit()"' EXIT
  setting trap
  traps: trap -- 'echo "func-exit()"' EXIT
exiting echoTraps()

===== calling '( echoTraps; ) | cat'
entering echoTraps()
  traps:
  setting trap
  traps: trap -- 'echo "func-exit()"' EXIT
exiting echoTraps()
func-exit()

===== calling '{ echoTraps; } | cat'
entering echoTraps()
  traps: trap -- 'echo "main-exit()"' EXIT
  setting trap
  traps: trap -- 'echo "func-exit()"' EXIT
exiting echoTraps()
func-exit()

main-exit()

底线：不要依赖这样的极端情况。我记得调查过关于子外壳和管道的其他不一致（不是关于陷阱），并试图将我的头绕在bash源代码上，你不想走那条路并试图理解为什么它在某些情况下的行为如此（代码真的很可怕，顺便说一句）。如您所见，有些事情似乎已经“修复”和/但我的两个示例的行为已经与您的不同。

于 2014-03-06T15:37:24.027 回答