Scala 中的正则表达式

正则表达式解释了用于匹配一系列输入数据的常见模式，因此它有助于许多编程语言中的模式匹配。在 Scala 中，正则表达式通常被称为 Scala Regex 。
Regex是一个从scala.util.matching.Regex包中导入的类，广泛应用于搜索和文本解析。为了将字符串重铸成正则表达式，我们需要使用r()方法来指定字符串。

例子：

// Scala program for Regular 
// Expressions
  
// Creating object
object GfG 
{
  
    // Main method
    def main(args: Array[String]) 
    {
      
        // Applying r() method
        val portal = "GeeksforGeeks".r
        val CS = "GeeksforGeeks is a CS portal."
  
        // Displays the first match
        println(portal findFirstIn CS)
    }
}

输出：

Some(GeeksforGeeks)

在这里，我们在所述字符串上调用了方法r()以获取Regex class的实例，以创建模式。上面的代码中使用了findFirstIn()方法来查找正则表达式的第一个匹配项。为了找到表达式中的所有匹配词，请使用findAllIn()方法。

例子：

// Scala program for Regular 
// Expressions
import scala.util.matching.Regex
  
// Creating object
object GfG 
{
  
    // Main method
    def main(args: Array[String]) 
    {
      
        // Applying Regex class
        val x = new Regex("Nidhi")
        val myself = "My name is Nidhi Singh."
  
        // replaces first match with the
        // String given below
        println(x replaceFirstIn(myself, "Rahul"))
    }
}

输出：

My name is Rahul Singh.

我们甚至可以使用 Regex 的构造函数来代替r()方法。在这里， replaceFirstIn()方法用于替换指定字符串的第一个匹配项，我们甚至可以使用replaceAllIn()方法替换所有匹配项。

例子：

// Scala program for Regular 
// Expressions
import scala.util.matching.Regex
  
// Creating object
object GfG 
{
  
    // Main method
    def main(args: Array[String]) 
    {
      
        // Applying Regex class
        val Geeks = new Regex("(G|g)fG")
        val y = "GfG is a CS portal. I like gfG"
  
        // Displays all the matches separated
        // by a separator
        println((Geeks findAllIn y).mkString(", "))
    }
}

输出：

GfG, gfG

在这里，我们使用mkString方法连接所有匹配项，用分隔符分隔，并且在上面的代码中使用管道（ | ）在给定的字符串中搜索大小写。因此，此处返回所述字符串的大写和小写。

Scala 正则表达式的语法

Java继承了 Perl 的一些特性，Scala 继承了Java的 Scala 正则表达式的语法。下面是元字符语法列表：

Subexpression	Matches
^	It is used to match starting point of the line.
$	It is used to match terminating point of the line.
.	It is used to match any one character excluding the newline.
[…]	It is used to match any one character within the brackets.
[^…]	It is used to match any one character which is not in the brackets.
\\A	It is used to match starting point of the intact string.
\\z	It is used to match terminating point of the intact string.
\\Z	It is used to match end of the whole string excluding the new line, if it exists.
re*	It is utilized to match zero or more appearances of the foregoing expressions.
re+	It is used to match one or more of the foregoing expressions.
re?	It is used to match zero or one appearance of the foregoing expression.
re{ n}	It is used to matches precisely n number of appearances of the foregoing expression.
re{ n, }	It is used to match n or more appearances of the foregoing expression.
re{ n, m}	It is used to match at least n and at most m appearances of the foregoing expression.
q\|r	It is utilized to match either q or r.
(re)	It is utilized to group the Regular expressions and recollects the text that are matched.
(?: re)	It also groups the regular expressions but does not recollects the matched text.
(?> re)	It is utilized to match self-reliant pattern in absence of backtracking.
\\w	It is used to match characters of the word.
\\W	It is used to match characters of the non-word.
\\s	It is utilized to match white spaces which are analogous to [\t\n\r\f].
\\S	It is used to match non-white spaces.
\\d	It is used to match the digits i.e, [0-9].
\\D	It is used to match non-digits.
\\G	It is used to match the point where the endmost match overs.
\\n	It is used for back-reference to occupy group number n.
\\b	It is used to match the word frontiers when it is out of the brackets and matches the backspace when it is in the brackets.
\\B	It is used to match non-word frontiers.
\\n, \\t, etc.	It is used to match the newlines, tabs, etc.
\\Q	It is used to escape (quote) each of the characters till \\E.
\\E	It is used in ends quoting starting with \\Q.