以下是注定要崩溃的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(RH4机器与gcc 4.5.2)时,它可预测地给出了一个分段错误：
% ./a.out Segmentation fault % echo $status 139
如果我使用Perl v5.8.5运行它,会发生这种情况：
% perl -e 'system("./a.out") and die "Status: $?"'
Status: 11 at -e line 1.
perlvar文件的价格是多少？说
Thus,the exit value of the subprocess is really
($?>> 8 ),and$? &gives which signal,if any,the process died from,and
127$? & 128
reports whether there was a core dump.
11>> 8是0,11& 127是11.
为什么不同的退出状态？如果我们不能依赖退出状态,那么在外部命令中检测分段错误的方法应该是什么？
解决方法
阅读系统文档可能会回答您的问题：
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.