三、字符串
惯用C的程序员要注意，在PERL中，字符串的末尾并不含有隐含的NULL字符，NULL字符可以出现在串的任何位置。
. 双引号内的字符串中支持简单变量替换，例如：
$number = 11;
$text = "This text contains the number $number.";
则$text的内容为："This text contains the number 11."
.双引号内的字符串中支持转义字符
Table 3.1. Escape sequences in strings.
Escape Sequence Description
a Bell (beep)
b Backspace
cn The Ctrl+n character
e Escape
E Ends the effect of L, U or Q
f Form feed
l Forces the next letter into lowercase
L All following letters are lowercase
n Newline
r Carriage return
Q Do not look for special pattern characters
t Tab
u Force next letter into uppercase
U All following letters are uppercase
v Vertical tab
L、U、Q功能可以由E关闭掉，如：
$a = "TLHIS IS A ESTRING"; # same as "This is a STRING"
.要在字符串中包含双引号或反斜线，则在其前加一个反斜线，反斜线还可以取消变量替换，如：
$res = "A quote " and A backslash ";
$result = 14;
print ("The value of $result is $result.n")的结果为：
The value of $result is 14.
.可用nnn(8进制)或xnn(16进制)来表示ASCII字符，如：
$result = "377"; # this is the character 255,or EOF
$result = "xff"; # this is also 255
.单引号字符串
单引号字符串与双引号字符串有两个区别，一是没有变量替换功能，二是反斜线不支持转义字符，而只在包含单引号和反斜线时起作用。单引号另一个特性是可以跨多行，如：
$text = 'This is two
lines of text
';
与下句等效：
$text = "This is twonlines of textn";
.字符串和数值的互相转换
例1：
$string = "43";
$number = 28;
$result = $string + $number; # $result = 71
若字符串中含有非数字的字符，则从左起至第一个非数字的字符，如：
$result = "hello" * 5; # $result = 0
$result = "12a34" +1; # $result = 13
.变量初始值
在PERL中，所有的简单变量都有缺省初始值：""，即空字符。但是建议给所有变量赋初值，否则当程序变得大而复杂后，很容易出现不可预料且很难调试的错误。