Class scala.util.matching.Regex

Companion object Regex

class Regex extends Serializable

A regular expression is used to determine whether a string matches a pattern and, if it does, to extract or transform the parts that match.

Usage

This class delegates to the java.util.regex package of the Java Platform. See the documentation for java.util.regex.Pattern for details about the regular expression syntax for pattern strings.

An instance of Regex represents a compiled regular expression pattern. Since compilation is expensive, frequently used Regexes should be constructed once, outside of loops and perhaps in a companion object.

The canonical way to create a Regex is by using the method r, provided implicitly for strings:

val date = raw"(\d{4})-(\d{2})-(\d{2})".r

Since escapes are not processed in multi-line string literals, using triple quotes avoids having to escape the backslash character, so that "\\d" can be written """\d""". The same result is achieved with certain interpolators, such as raw"\d".r or a custom interpolator r"\d" that also compiles the Regex.

Extraction

To extract the capturing groups when a Regex is matched, use it as an extractor in a pattern match:

"2004-01-20" match {
  case date(year, month, day) => s"$year was a good year for PLs."
}

To check only whether the Regex matches, ignoring any groups, use a sequence wildcard:

"2004-01-20" match {
  case date(_*) => "It's a date!"
}

That works because a Regex extractor produces a sequence of strings. Extracting only the year from a date could also be expressed with a sequence wildcard:

"2004-01-20" match {
  case date(year, _*) => s"$year was a good year for PLs."
}

In a pattern match, Regex normally matches the entire input. However, an unanchored Regex finds the pattern anywhere in the input.

val embeddedDate = date.unanchored
"Date: 2004-01-20 17:25:18 GMT (10 years, 28 weeks, 5 days, 17 hours and 51 minutes ago)" match {
  case embeddedDate("2004", "01", "20") => "A Scala is born."
}
Find Matches

To find or replace matches of the pattern, use the various find and replace methods. For each method, there is a version for working with matched strings and another for working with Match objects.

For example, pattern matching with an unanchored Regex, as in the previous example, can also be accomplished using findFirstMatchIn. The findFirst methods return an Option which is non-empty if a match is found, or None for no match:

val dates = "Important dates in history: 2004-01-20, 1958-09-05, 2010-10-06, 2011-07-15"
val firstDate = date.findFirstIn(dates).getOrElse("No date found.")
val firstYear = for (m <- date.findFirstMatchIn(dates)) yield m.group(1)

To find all matches:

val allYears = for (m <- date.findAllMatchIn(dates)) yield m.group(1)

To check whether input is matched by the regex:

date.matches("2018-03-01")                     // true
date.matches("Today is 2018-03-01")            // false
date.unanchored.matches("Today is 2018-03-01") // true

To iterate over the matched strings, use findAllIn, which returns a special iterator that can be queried for the MatchData of the last match:

val mi = date.findAllIn(dates)
while (mi.hasNext) {
  val d = mi.next
  if (mi.group(1).toInt < 1960) println(s"$d: An oldie but goodie.")
}

Although the MatchIterator returned by findAllIn is used like any Iterator, with alternating calls to hasNext and next, hasNext has the additional side effect of advancing the underlying matcher to the next unconsumed match. This effect is visible in the MatchData representing the "current match".

val r = "(ab+c)".r
val s = "xxxabcyyyabbczzz"
r.findAllIn(s).start    // 3
val mi = r.findAllIn(s)
mi.hasNext              // true
mi.start                // 3
mi.next()               // "abc"
mi.start                // 3
mi.hasNext              // true
mi.start                // 9
mi.next()               // "abbc"

The example shows that methods on MatchData such as start will advance to the first match, if necessary. It also shows that hasNext will advance to the next unconsumed match, if next has already returned the current match.

The current MatchData can be captured using the matchData method. Alternatively, findAllMatchIn returns an Iterator[Match], where there is no interaction between the iterator and Match objects it has already produced.

Note that findAllIn finds matches that don't overlap. (See findAllIn for more examples.)

val num = raw"(\d+)".r
val all = num.findAllIn("123").toList  // List("123"), not List("123", "23", "3")
Replace Text

Text replacement can be performed unconditionally or as a function of the current match:

val redacted    = date.replaceAllIn(dates, "XXXX-XX-XX")
val yearsOnly   = date.replaceAllIn(dates, m => m.group(1))
val months      = (0 to 11).map { i => val c = Calendar.getInstance; c.set(2014, i, 1); f"$c%tb" }
val reformatted = date.replaceAllIn(dates, _ match { case date(y,m,d) => f"${months(m.toInt - 1)} $d, $y" })

Pattern matching the Match against the Regex that created it does not reapply the Regex. In the expression for reformatted, each date match is computed once. But it is possible to apply a Regex to a Match resulting from a different pattern:

val docSpree = """2011(?:-\d{2}){2}""".r
val docView  = date.replaceAllIn(dates, _ match {
  case docSpree() => "Historic doc spree!"
  case _          => "Something else happened"
})
Self Type
Regex
Annotations
@SerialVersionUID()
Source
Regex.scala
See also

java.util.regex.Pattern

Linear Supertypes
java.io.Serializable, AnyRef, Any
Known Subclasses
UnanchoredRegex

Instance Constructors

new Regex(regex: String, groupNames: String*)

Compile a regular expression, supplied as a string, into a pattern that can be matched against inputs.

If group names are supplied, they can be used this way:

val namedDate  = new Regex("""(\d\d\d\d)-(\d\d)-(\d\d)""", "year", "month", "day")
val namedYears = for (m <- namedDate findAllMatchIn dates) yield m group "year"

Group names supplied to the constructor are preferred to inline group names when retrieving matched groups by name. Not all platforms support inline names.

This constructor does not support options as flags, which must be supplied as inline flags in the pattern string: (?idmsux-idmsux).

regex

The regular expression to compile.

groupNames

Names of capturing groups.

Value Members

final def !=(arg0: Any): Boolean

Test two objects for inequality.

returns

true if !(this == that), false otherwise.

Definition Classes
AnyRef → Any

final def ##(): Int

Equivalent to x.hashCode except for boxed numeric types and null. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For null returns a hashcode where null.hashCode throws a NullPointerException.

returns

a hash value consistent with ==

Definition Classes
AnyRef → Any

def +(other: String): String

Implicit
This member is added by an implicit conversion from Regex toany2stringadd[Regex] performed by method any2stringadd in scala.Predef.
Definition Classes
any2stringadd

def ->[B](y: B): (Regex, B)

Implicit
This member is added by an implicit conversion from Regex toArrowAssoc[Regex] performed by method ArrowAssoc in scala.Predef.
Definition Classes
ArrowAssoc
Annotations
@inline()

final def ==(arg0: Any): Boolean

The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

returns

true if the receiver object is equivalent to the argument; false otherwise.

Definition Classes
AnyRef → Any

def anchored: Regex

final def asInstanceOf[T0]: T0

Cast the receiver object to be of type T0.

Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.

returns

the receiver object.

Definition Classes
Any
Exceptions thrown

ClassCastException if the receiver object is not an instance of the erasure of type T0.

def clone(): AnyRef

Create a copy of the receiver object.

The default implementation of the clone method is platform dependent.

returns

a copy of the receiver object.

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.CloneNotSupportedException]) @native()
Note

not specified by SLS as a member of AnyRef

def ensuring(cond: (Regex) => Boolean, msg: => Any): Regex

Implicit
This member is added by an implicit conversion from Regex toEnsuring[Regex] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring

def ensuring(cond: (Regex) => Boolean): Regex

Implicit
This member is added by an implicit conversion from Regex toEnsuring[Regex] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring

def ensuring(cond: Boolean, msg: => Any): Regex

Implicit
This member is added by an implicit conversion from Regex toEnsuring[Regex] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring

def ensuring(cond: Boolean): Regex

Implicit
This member is added by an implicit conversion from Regex toEnsuring[Regex] performed by method Ensuring in scala.Predef.
Definition Classes
Ensuring

final def eq(arg0: AnyRef): Boolean

Tests whether the argument (that) is a reference to the receiver object (this).

The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:

    It is consistent: for any non-null instances x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false. null.eq(null) returns true.

When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).

returns

true if the argument is a reference to the receiver object; false otherwise.

Definition Classes
AnyRef

def equals(arg0: AnyRef): Boolean

The equality method for reference types. Default implementation delegates to eq.

See also equals in scala.Any.

returns

true if the receiver object is equivalent to the argument; false otherwise.

Definition Classes
AnyRef → Any

def finalize(): Unit

Called by the garbage collector on the receiver object when there are no more references to the object.

The details of when and if the finalize method is invoked, as well as the interaction between finalize and non-local returns and exceptions, are all platform dependent.

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.Throwable])
Note

not specified by SLS as a member of AnyRef

def findAllIn(source: CharSequence): MatchIterator

Return all non-overlapping matches of this Regex in the given character sequence as a scala.util.matching.Regex.MatchIterator, which is a special scala.collection.Iterator that returns the matched strings but can also be queried for more data about the last match, such as capturing groups and start position.

A MatchIterator can also be converted into an iterator that returns objects of type scala.util.matching.Regex.Match, such as is normally returned by findAllMatchIn.

Where potential matches overlap, the first possible match is returned, followed by the next match that follows the input consumed by the first match:

val hat  = "hat[^a]+".r
val hathaway = "hathatthattthatttt"
val hats = hat.findAllIn(hathaway).toList                     // List(hath, hattth)
val pos  = hat.findAllMatchIn(hathaway).map(_.start).toList   // List(0, 7)

To return overlapping matches, it is possible to formulate a regular expression with lookahead (?=) that does not consume the overlapping region.

val madhatter = "(h)(?=(at[^a]+))".r
val madhats   = madhatter.findAllMatchIn(hathaway).map {
  case madhatter(x,y) => s"$x$y"
}.toList                                       // List(hath, hatth, hattth, hatttt)

Attempting to retrieve match information after exhausting the iterator results in java.lang.IllegalStateException. See scala.util.matching.Regex.MatchIterator for details.

source

The text to match against.

returns

A scala.util.matching.Regex.MatchIterator of matched substrings.

Example:
    for (words <- """\w+""".r findAllIn "A simple example.") yield words

def findAllMatchIn(source: CharSequence): Iterator[Match]

Return all non-overlapping matches of this regexp in given character sequence as a scala.collection.Iterator of scala.util.matching.Regex.Match.

source

The text to match against.

returns

A scala.collection.Iterator of scala.util.matching.Regex.Match for all matches.

Example:
    for (words <- """\w+""".r findAllMatchIn "A simple example.") yield words.start

def findFirstIn(source: CharSequence): Option[String]

Return an optional first matching string of this Regex in the given character sequence, or None if there is no match.

source

The text to match against.

returns

An scala.Option of the first matching string in the text.

Example:
    """\w+""".r findFirstIn "A simple example." foreach println // prints "A"

def findFirstMatchIn(source: CharSequence): Option[Match]

Return an optional first match of this Regex in the given character sequence, or None if it does not exist.

If the match is successful, the scala.util.matching.Regex.Match can be queried for more data.

source

The text to match against.

returns

A scala.Option of scala.util.matching.Regex.Match of the first matching string in the text.

Example:
    ("""[a-z]""".r findFirstMatchIn "A simple example.") map (_.start) // returns Some(2), the index of the first match in the text

def findPrefixMatchOf(source: CharSequence): Option[Match]

Return an optional match of this Regex at the beginning of the given character sequence, or None if it matches no prefix of the character sequence.

Unlike findFirstMatchIn, this method will only return a match at the beginning of the input.

source

The text to match against.

returns

A scala.Option of the scala.util.matching.Regex.Match of the matched string.

Example:
    """\w+""".r findPrefixMatchOf "A simple example." map (_.after) // returns Some(" simple example.")

def findPrefixOf(source: CharSequence): Option[String]

Return an optional match of this Regex at the beginning of the given character sequence, or None if it matches no prefix of the character sequence.

Unlike findFirstIn, this method will only return a match at the beginning of the input.

source

The text to match against.

returns

A scala.Option of the matched prefix.

Example:
    """\p{Lower}""".r findPrefixOf "A simple example." // returns None, since the text does not begin with a lowercase letter

def formatted(fmtstr: String): String

Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).

Implicit
This member is added by an implicit conversion from Regex toStringFormat[Regex] performed by method StringFormat in scala.Predef.
Definition Classes
StringFormat
Annotations
@inline()

final def getClass(): Class[_ <: AnyRef]

Returns the runtime class representation of the object.

returns

a class object corresponding to the runtime type of the receiver.

Definition Classes
AnyRef → Any
Annotations
@native()

def hashCode(): Int

The hashCode method for reference types. See hashCode in scala.Any.

returns

the hash code value for this object.

Definition Classes
AnyRef → Any
Annotations
@native()

final def isInstanceOf[T0]: Boolean

Test whether the dynamic type of the receiver object is T0.

Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression 1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.

returns

true if the receiver object is an instance of erasure of type T0; false otherwise.

Definition Classes
Any

def matches(source: CharSequence): Boolean

Returns whether this Regex matches the given character sequence.

Like the extractor, this method takes anchoring into account.

source

The text to match against

returns

true if and only if source matches this Regex.

Example:
    """\d+""".r matches "123" // returns true
See also

Regex#unanchored

final def ne(arg0: AnyRef): Boolean

Equivalent to !(this eq that).

returns

true if the argument is not a reference to the receiver object; false otherwise.

Definition Classes
AnyRef

final def notify(): Unit

Wakes up a single thread that is waiting on the receiver object's monitor.

Definition Classes
AnyRef
Annotations
@native()
Note

not specified by SLS as a member of AnyRef

final def notifyAll(): Unit

Wakes up all threads that are waiting on the receiver object's monitor.

Definition Classes
AnyRef
Annotations
@native()
Note

not specified by SLS as a member of AnyRef

val pattern: Pattern

def regex: String

def replaceAllIn(target: CharSequence, replacer: (Match) => String): String

Replaces all matches using a replacer function. The replacer function takes a scala.util.matching.Regex.Match so that extra information can be obtained from the match. For example:

import scala.util.matching.Regex
val datePattern = new Regex("""(\d\d\d\d)-(\d\d)-(\d\d)""", "year", "month", "day")
val text = "From 2011-07-15 to 2011-07-17"
val repl = datePattern replaceAllIn (text, m => s"${m group "month"}/${m group "day"}")

In the replacement String, a dollar sign ($) followed by a number will be interpreted as a reference to a group in the matched pattern, with numbers 1 through 9 corresponding to the first nine groups, and 0 standing for the whole match. Any other character is an error. The backslash (\) character will be interpreted as an escape character and can be used to escape the dollar sign. Use Regex.quoteReplacement to escape these characters.

target

The string to match.

replacer

The function which maps a match to another string.

returns

The target string after replacements.

def replaceAllIn(target: CharSequence, replacement: String): String

Replaces all matches by a string.

In the replacement String, a dollar sign ($) followed by a number will be interpreted as a reference to a group in the matched pattern, with numbers 1 through 9 corresponding to the first nine groups, and 0 standing for the whole match. Any other character is an error. The backslash (\) character will be interpreted as an escape character and can be used to escape the dollar sign. Use Regex.quoteReplacement to escape these characters.

target

The string to match

replacement

The string that will replace each match

returns

The resulting string

Example:
    """\d+""".r replaceAllIn ("July 15", "<NUMBER>") // returns "July <NUMBER>"

def replaceFirstIn(target: CharSequence, replacement: String): String

Replaces the first match by a string.

In the replacement String, a dollar sign ($) followed by a number will be interpreted as a reference to a group in the matched pattern, with numbers 1 through 9 corresponding to the first nine groups, and 0 standing for the whole match. Any other character is an error. The backslash (\) character will be interpreted as an escape character and can be used to escape the dollar sign. Use Regex.quoteReplacement to escape these characters.

target

The string to match

replacement

The string that will replace the match

returns

The resulting string

def replaceSomeIn(target: CharSequence, replacer: (Match) => Option[String]): String

Replaces some of the matches using a replacer function that returns an scala.Option. The replacer function takes a scala.util.matching.Regex.Match so that extra information can be obtained from the match. For example:

import scala.util.matching.Regex._

val vars = Map("x" -> "a var", "y" -> """some $ and \ signs""")
val text = "A text with variables %x, %y and %z."
val varPattern = """%(\w+)""".r
val mapper = (m: Match) => vars get (m group 1) map (quoteReplacement(_))
val repl = varPattern replaceSomeIn (text, mapper)

In the replacement String, a dollar sign ($) followed by a number will be interpreted as a reference to a group in the matched pattern, with numbers 1 through 9 corresponding to the first nine groups, and 0 standing for the whole match. Any other character is an error. The backslash (\) character will be interpreted as an escape character and can be used to escape the dollar sign. Use Regex.quoteReplacement to escape these characters.

target

The string to match.

replacer

The function which optionally maps a match to another string.

returns

The target string after replacements.

def runMatcher(m: Matcher): Boolean

Attributes
protected

def split(toSplit: CharSequence): Array[String]

Splits the provided character sequence around matches of this regexp.

toSplit

The character sequence to split

returns

The array of strings computed by splitting the input around matches of this regexp

final def synchronized[T0](arg0: => T0): T0

Definition Classes
AnyRef

def toString(): String

The string defining the regular expression

returns

a String representation of the object.

Definition Classes
Regex → AnyRef → Any

def unanchored: UnanchoredRegex

Create a new Regex with the same pattern, but no requirement that the entire String matches in extractor patterns and Regex#matches.

Normally, matching on date behaves as though the pattern were enclosed in anchors, "^pattern$".

The unanchored Regex behaves as though those anchors were removed.

Note that this method does not actually strip any matchers from the pattern.

Calling anchored returns the original Regex.

val date = """(\d\d\d\d)-(\d\d)-(\d\d)""".r.unanchored

val date(year, month, day) = "Date 2011-07-15"                       // OK

val copyright: String = "Date of this document: 2011-07-15" match {
  case date(year, month, day) => s"Copyright $year"                  // OK
  case _                      => "No copyright"
}
returns

The new unanchored regex

def unapplySeq(m: Match): Option[List[String]]

Tries to match on a scala.util.matching.Regex.Match.

A previously failed match results in None.

If a successful match was made against the current pattern, then that result is used.

Otherwise, this Regex is applied to the previously matched input, and the result of that match is used.

def unapplySeq(c: Char): Option[List[Char]]

Tries to match the String representation of a scala.Char.

If the match succeeds, the result is the first matching group if any groups are defined, or an empty Sequence otherwise.

For example:

val cat = "cat"
// the case must consume the group to match
val r = """(\p{Lower})""".r
cat(0) match { case r(x) => true }
cat(0) match { case r(_) => true }
cat(0) match { case r(_*) => true }
cat(0) match { case r() => true }     // no match

// there is no group to extract
val r = """\p{Lower}""".r
cat(0) match { case r(x) => true }    // no match
cat(0) match { case r(_) => true }    // no match
cat(0) match { case r(_*) => true }   // matches
cat(0) match { case r() => true }     // matches

// even if there are multiple groups, only one is returned
val r = """((.))""".r
cat(0) match { case r(_) => true }    // matches
cat(0) match { case r(_,_) => true }  // no match
c

The Char to match

returns

The match

def unapplySeq(s: CharSequence): Option[List[String]]

Tries to match a java.lang.CharSequence.

If the match succeeds, the result is a list of the matching groups (or a null element if a group did not match any input). If the pattern specifies no groups, then the result will be an empty list on a successful match.

This method attempts to match the entire input by default; to find the next matching subsequence, use an unanchored Regex.

For example:

val p1 = "ab*c".r
val p1Matches = "abbbc" match {
  case p1() => true               // no groups
  case _    => false
}
val p2 = "a(b*)c".r
val p2Matches = "abbbc" match {
  case p2(_*) => true             // any groups
  case _      => false
}
val numberOfB = "abbbc" match {
  case p2(b) => Some(b.length)    // one group
  case _     => None
}
val p3 = "b*".r.unanchored
val p3Matches = "abbbc" match {
  case p3() => true               // find the b's
  case _    => false
}
val p4 = "a(b*)(c+)".r
val p4Matches = "abbbcc" match {
  case p4(_*) => true             // multiple groups
  case _      => false
}
val allGroups = "abbbcc" match {
  case p4(all @ _*) => all mkString "/" // "bbb/cc"
  case _            => ""
}
val cGroup = "abbbcc" match {
  case p4(_, c) => c
  case _        => ""
}
s

The string to match

returns

The matches

final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

final def wait(arg0: Long, arg1: Int): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException]) @native()

© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.13.0/scala/util/matching/Regex.html