Regex

@SerialVersionUID(-2094783597747625537L) 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" })
Value Params
groupNames

A mapping from names to indices in capture groups

pattern

The compiled pattern

See also
Companion
object
Source
Regex.scala
class Object
trait Matchable
class Any

Value members

Constructors

def this(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).

Value Params
groupNames

Names of capturing groups.

regex

The regular expression to compile.

Source
Regex.scala

Concrete methods

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.

Value Params
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
Source
Regex.scala

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

Value Params
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
Source
Regex.scala

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

Value Params
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"
Source
Regex.scala

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.

Value Params
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
Source
Regex.scala

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.

Value Params
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.")
Source
Regex.scala

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.

Value Params
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
Source
Regex.scala

Returns whether this Regex matches the given character sequence.

Like the extractor, this method takes anchoring into account.

Value Params
source

The text to match against

Returns

true if and only if source matches this Regex.

See also
Example

"""\d+""".r matches "123" // returns true
Source
Regex.scala
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.

Value Params
replacement

The string that will replace each match

target

The string to match

Returns

The resulting string

Example

"""\d+""".r replaceAllIn ("July 15", "") // returns "July "
Source
Regex.scala
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.

Value Params
replacer

The function which maps a match to another string.

target

The string to match.

Returns

The target string after replacements.

Source
Regex.scala
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.

Value Params
replacement

The string that will replace the match

target

The string to match

Returns

The resulting string

Source
Regex.scala
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.

Value Params
replacer

The function which optionally maps a match to another string.

target

The string to match.

Returns

The target string after replacements.

Source
Regex.scala
def split(toSplit: CharSequence): Array[String]

Splits the provided character sequence around matches of this regexp.

Value Params
toSplit

The character sequence to split

Returns

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

Source
Regex.scala
override def toString: String

The string defining the regular expression

Definition Classes
Any
Source
Regex.scala

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

Source
Regex.scala

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 _ => "" }
Value Params
s

The string to match

Returns

The matches

Source
Regex.scala

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
Value Params
c

The Char to match

Returns

The match

Source
Regex.scala

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.

Concrete fields