Perl |比较标量
先决条件:Perl 中的标量
Perl 有两种类型的比较运算符集。就像其他数学运算符一样，这些运算符不是执行运算，而是比较标量。有两种类型的 Perl 比较运算符集。 一个是数值标量值，一个是字符串标量值。下表说明了这两种类型:
| 数字的 | 线 | 描述 |
|---|---|---|
| == | 情商 | 等于 |
| ！= | -不知道 | 不等于 |
| < | 它 | 小于 |
| > | 大型旅行车的 | 大于 |
| <= | 务实贸易(Labor Exchange)ˌ低爆速炸药(Low Explosive)ˌ职业介绍所(Labour Exchange) | 小于或等于 |
| >= | 通用电气公司 | 大于或等于 |
以上数值和字符串标量比较运算符的说明:
-
== and eq : This operator is used to check the equality. In the following code, outputs of codes after using == and eq is compared and showing how it work for numeric and string scalars differently.
例 1:
```perl
Perl program to illustrate
== operator
taking two numeric scalars
$x = 5; $y = 5;
using "==" operator
if($x == $y) { print "== works with numeric value!"; } ```
输出:
```perl == works with numeric value!
```
例 2:
```perl
Perl program to illustrate
== and eq operator
string scalar
$str = "geekforgeeks";
if($str == "GEEKSFORGEEKS") { print "== doesn't work with string values!";
}
comparing with capital string
if($str eq "GEEKSFORGEEKS") { print "eq works with string values!"; } ```
输出:
```perl == doesn't work with string values!
```
说明:在示例 2 的输出中，因为$str 和 GEEKSFORGEEKS 不相等，所以不会执行 Last print 语句。另外，“G”和“G”的 ASCII 码是不同的。因此，==适用于数值，但不适用于字符串值，eq 仅适用于字符串标量。
-
!= and ne
在下面的代码中，比较了使用后的输出！=和 ne，并显示了哪一个适合字符串，哪一个适合数值标量值。
例 1:
```perl
Perl program to demonstrate the
!= operator
numeric scalars
$x = 5; $y = 10;
using != operator
if($x != $y) { print "!= works with numeric value!"; } ```
输出:
```perl != works with numeric value!
```
例 2:
```perl
Perl program to demonstrate the
!= and ne operator
string scalar
$str = "geekforgeeks";
using != operator
if($str != "GEEKSFORGEEKS") { print "\n!= doesn't work with string values!";
}
comparing with capital string
if($str ne "GEEKSFORGEEKS") { print"ne works with string values!"; } ```
输出:
```perl ne works with string values!
```
说明:在第二个例子中，不会执行第一个 print 语句，因为！=将两个字符串都转换为 0。因此！=适用于数值，但不适用于字符串值，ne 适用于字符串标量。
-
(> or gt) And (< or lt)
在下面的代码中，我们将比较使用(>或 gt)和(
例 1:
```perl
Perl program to demonstrate the
(> or gt) And (< or lt)
operator
numeric scalars
$x = 4; $y = 5;
using (> or gt) And (< or lt)
if(($x < \(y) and (\)x lt $y) ) { print "< and lt works with numeric value!"; }
if(($y > \(x) and (\)y gt $x) ) { print "\n> and gt works with numeric value!"; } ```
输出:
```perl < and lt works with numeric value!
and gt works with numeric value!
```
例 2:
```perl
Perl program to demonstrate the
(> or gt) And (< or lt)
operator
string scalar
$str = "geekforgeeks";
if($str < "GEEKSFORGEEKS") { print "< doesn't work with string values!"; }
comparing with capital string
if($str lt "GEEKSFORGEEKSZZZ") { print"lt works with string values!"; }
comparing with capital string
if($str gt "GEEKSFORGEEKSZZZ") { print"gt works with string values!"; }
comparing with capital string
if($str lt "kEEKSFORGEEKS") { print"\nlt works with string values!"; } ```
输出:
```perl gt works with string values! lt works with string values!
```
解释:上面的代码告诉我们一些关于 Perl 如何处理字符串的有趣的事情。第一个例子的输出非常明显，因为字符串和数值运算符都以同样的方式对待数值标量。 但是在第二个输出中，“lt”并没有像我们预期的那样表现。假设 Perl 的“lt”运算符不区分大小写，但我们甚至在后面加上了“ZZZ”，即使在这种情况下,$str 也不小于引号中的字符串，下一个输出显示它更大。从第二个例子输出的第二行 可以清楚地看到这一点，Perl 的字符串运算符只需首先检查字符串的第一个字符，然后比较 ASCII 码。因为在 ASCII 表中，大写字母排在第一位。Perl 编译器匹配第一个字母，然后匹配其余字母。
-
(>= or ge) And (<= or le)
这些操作符也处理 ASCII 值，在字符串操作符的情况下进行检查。如果是数值运算符，则检查该值。
示例:
```perl
Perl program to demonstrate the
(>= or ge) And (<= or le)
operator
numeric scalars
$x = 5; $y = 10;
if(($x <= \(y) and (\)y >= $x)) { print "<= and>= works"; }
string scalar
$str= "geeksforgeeks";
if ((\(str le "keeksforgeeks") and (\)str ge "feeksforgeeks")) { print "\nle and ge works!"; }
```
输出:
```perl <= and>= works le and ge works!
```
需要记住的要点:
-
Numeric operator will always convert String values to 0. When we compare two string scalars with Numeric operators like ==, >= or <= then it will always convert the scalars to 0 or 0.0. Since they are not a string. And hence it will be true in case of ==, >= or <= as shown in the below example:
```perl
Perl program to illustrate
above point
numeric scalars
$x = "BBB"; $y = "aaa";
if (($x == \(y and (\)x <= \(y) and (\)x >= $y))) { print "True"; } ```
输出:
```perl True
```
解释:在上面的代码中，“aaa”在各个方面都小于 BBB(小写，也是 ASCII 的 a 大于 B)，但是两个字符串仍然是相等的，因为数值比较运算符将字符串转换为 0。
-
String operator doesn’t compare numeric values, instead it compares there ASCII values. String operators compare ASCII values for numeric values. In the following example “9 gt 17” is true but “17 gt 9” will give the result as false.
```perl
Perl program to illustrate
above point
numeric scalar
$x = 9; $y = 17;
if ($x gt $y) { print "True"; } ```
输出:
```perl True
```
-
