perl - 在 perl 中，我们如何检测外部命令中的段错误

Question

以下是注定会崩溃的 C 代码:

#include<stdio.h>
#include<stdlib.h>

int main() {
    char *p = NULL;
    printf("Value at P: %c\n", *p);
    return 0;
}

当我编译并运行它(带有 gcc 4.5.2 的 RH4 机器)时，它可以预见地给出一个段错误:

%  ./a.out
Segmentation fault

%  echo $status
139

如果我用 Perl v5.8.5 运行它，会发生这种情况:

%  perl -e 'system("./a.out") and die "Status: $?"'
Status: 11 at -e line 1.

perlvar $? 的文档说

Thus, the exit value of the subprocess is really ($?>> 8 ), and $? &
127 gives which signal, if any, the process died from, and $? & 128 reports whether there was a core dump.

11 >> 8是 0 , 和 11 & 127是 11 .

为什么退出状态不同？如果我们不能依赖退出状态，那么在外部命令中检测段错误的方法应该是什么？

Answer 1

阅读 system 的文档可能会回答你的问题:

system('a.out');

if ($? == -1) {
    print "failed to execute: $!\n";
}
elsif ($? & 127) {
    printf "child died with signal %d, %s coredump\n",
        ($? & 127),  ($? & 128) ? 'with' : 'without';
}
else {
    printf "child exited with value %d\n", $? >> 8;
}

输出:

child died with signal 11, without coredump

shell 只是以不同的方式对状态中的信号进行编码:139 - 128 = 11。例如， man bash说:

The return value of a simple command is its exit status, or 128+n if the command is terminated by signal n.