全局符號「@str」需要明確的包名

Question

我是新用Perl，我已經面臨這個問題：

Global symbol "@str" requires explicit package name (did you forget to declare "my @str"?) at F:\Distrib\LingUtils9\Scripts\CompareLists\CompareLists.pl line 167 

一段代碼，導致此消息，可以作爲一個PROGRAMM，但不起作用。這是它：

my $containsSub = 0; 
my $str = "This is a string!"; 
my $substr = "string"; 
my $indexOfSub = index($str, $substr); 
if ($indexOfSub != -1) 
{ 
    if (length($substr)==length($str)) 
    { 
      $containsSub = 1; 
    } 
    elsif (($indexOfSub == 0)&&(($str[$indexOfSub + length($substr)]=='?')||($str[$indexOfSub + length($substr)]=='!')||($str[$indexOfSub + length($substr)]=='.')||($str[$indexOfSub + length($substr)]==' ')||($str[$indexOfSub + length($substr)]=='\t'))) 
    { 
      $containsSub = 1; 
    } 
    elsif ((length($str) == $indexOfSub + length($substr))&&(($str[$indexOfSub-1]=='.')||($str[$indexOfSub-1]==' ')||($str[$indexOfSub-1]=='\t')||($str[$indexOfSub-1]=='?')||($str[$indexOfSub-1]=='.')||($str[$indexOfSub-1]=='!'))) 
    { 
      $containsSub = 1; 
    } 
    elsif ((($str[$indexOfSub-1]=='?')||($str[$indexOfSub-1]=='!')||($str[$indexOfSub-1]=='.')||($str[$indexOfSub-1]==' ')||($str[$indexOfSub-1]=='\t'))||(($str[$indexOfSub+length($substr)]=='?')||($str[$indexOfSub+length($substr)]=='!')||($str[$indexOfSub+length($substr)]=='.')||($str[$indexOfSub+length($substr)]==' ')||($str[$indexOfSub+length($substr)]=='\t'))) 
    { 
      $containsSub = 1; 
    } 
} 
print $containsSub; 

這是非常原始的行中的子行內容驗證，並且它工作正常。但是，這（只是copypaste）：

sub containsKey 
{ 
    my $containsSub = 0; 
    my $str = "This is a string!"; 
    my $substr = "string"; 
    my $indexOfSub = index($str, $substr); 
    if ($indexOfSub != -1) 
    { 
     if (length($substr)==length($str)) 
     { 
      $containsSub = 1; 
     } 
     elsif (($indexOfSub == 0)&&(($str[$indexOfSub + length($substr)]=='?')||($str[$indexOfSub + length($substr)]=='!')||($str[$indexOfSub + length($substr)]=='.')||($str[$indexOfSub + length($substr)]==' ')||($str[$indexOfSub + length($substr)]=='\t'))) 
     { 
      $containsSub = 1; 
     } 
     elsif ((length($str) == $indexOfSub + length($substr))&&(($str[$indexOfSub-1]=='.')||($str[$indexOfSub-1]==' ')||($str[$indexOfSub-1]=='\t')||($str[$indexOfSub-1]=='?')||($str[$indexOfSub-1]=='.')||($str[$indexOfSub-1]=='!'))) 
     { 
      $containsSub = 1; 
     } 
     elsif ((($str[$indexOfSub-1]=='?')||($str[$indexOfSub-1]=='!')||($str[$indexOfSub-1]=='.')||($str[$indexOfSub-1]==' ')||($str[$indexOfSub-1]=='\t'))||(($str[$indexOfSub+length($substr)]=='?')||($str[$indexOfSub+length($substr)]=='!')||($str[$indexOfSub+length($substr)]=='.')||($str[$indexOfSub+length($substr)]==' ')||($str[$indexOfSub+length($substr)]=='\t'))) 
     { 
      $containsSub = 1; 
     } 
    } 
    return $containsSub; 
} 
my $keyContains = containsKey(); 

print $keyContains; 

使得在命令行

Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 16 
3. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 16 
3. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 16 
3. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 16 
3. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 16 
3. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 16 
7. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 16 
7. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 16 
7. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 16 
7. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 16 
7. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 16 
7. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 17 
1. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 17 
1. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 17 
1. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 17 
1. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 17 
1. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 17 
1. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 17 
1. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 17 
1. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 17 
1. 
Global symbol "@str" requires explicit package name (did you forget to declare " 
my @str"?) at \Compare.pl line 17 
1. 
Execution of \Compare.pl aborted 
due to compilation errors. 

這個輸出，我只是不明白那是什麼。

Answer 1

這是因爲perl字符串不是像某些語言中的字符數組。因此$str[3]不是訪問$str的有效方式。但是，它會訪問@str的第三個元素，該元素不存在並且尚未聲明，因此是警告。

如果您希望使用偏移量處理字符串，則需要substr。或my @chars_in_str = split //, $str;

更廣泛地說，雖然這看起來像一個相當骯髒的方式來嘗試和正則表達式匹配。

我建議你實際上想要做的是：

if ($str =~ m/\b$substr\b/) { 
    $containsSub = 1; 
} 

\b是「字邊界」 Perl的正則表達式，因此將匹配標點符號或空格的東西，雖然它不是嚴格的相當於你在做什麼（有一大堆更多的標點符號可以工作）。

您還應該注意 - 如果$substr包含元字符，它們將像正則表達式修飾符一樣工作。爲了避免這種情況，你需要\b\Q$substr\E\b關閉metachar處理。