当我在Perl中执行system()调用时,我通常会根据
perldocs检查返回代码.大部分时间$rc！= 0对我来说已经足够了.最近我帮了两个人,在apache下运行.cgi脚本时遇到了系统()调用问题.我指示他们检查$rc
my $rc = system(...);
并将它们链接到system()文档.然后我看得更近了,注意到文档并不是真的在谈论$rc,而是关于$？我感到有点尴尬,出现了以下问题：
是否有区别：
system(...);
if ($? == -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;
}
和
my $rc = system(...);
if ($rc == -1) {
print "Failed to execute: $!\n";
}
elsif ($rc & 127) {
printf "child died with signal %d,($rc & 127),($rc & 128) ? 'with' : 'without';
}
else {
printf "child exited with value %d\n",$rc >> 8;
}
或者,简而言之,$rc等于$？对于system()？
解决方法
是的,
system的回报值应等于$？
但是从$？不仅适用于系统调用和$？是一个全局变量,它可能被其他动作所覆盖.从perldoc -v’$？’这些包括：
$CHILD_ERROR
$?
The status returned by the last pipe close,backtick (““”) command,successful call to “wait()” or “waitpid()”,or from the “system()” operator.
保存值立即比较更安全：
my $rc = system('ls myfile.txt');
if ( $rc >> 8 != 0 ) {
# do something because ls exited with an error
}