SCRIPT1：

#!usr/bin/perl
#concatenation2.pl
use warnings;
use strict;
print"Four sevens are",4*7,"\n";
print"Four sevens are".4*7 ."\n";

SCRIPT2：

#!usr/bin/perl
#concatenation2.pl
use warnings;
use strict;
print"Four sevens are","\n";
print"Four sevens are".4*7."\n";

script1的输出是：

Four sevens are28
Four sevens are28

好的,所以我(了解到)在关闭双引号之前需要一个空格.
但是,script2的输出最终出现错误消息：

string found where operator expected at concatenate2.pl line 6,near "7."\n""
(Missing operator before "\n"?)
Syntax error at concatenate2.pl line 6,near "7."\n""

我无处可寻找解释为什么数字和数字之间需要有空格的原因.在script2中,数字之间不需要空格,
我目前依靠谷歌和免费的perl书来帮助我学习语言.任何帮助(这种细微差别的一般准则)将不胜感激.谢谢.