连接需要Perl中的"空间"吗？

Question

没有从谷歌的问题上找到任何解释,虽然我可能没有使用正确的搜索词.

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",4*7,"\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,虽然数字之间不需要空间,但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.

Answer 1

7.是perl词法分析器的数字,就像3.1415926535.为避免混淆,请使用空格将点与前一个数字分开:"the answer is " . 4*7 . " times more complicated".