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 Regex
es 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 parameters:
- groupNames
A mapping from names to indices in capture groups
- pattern
The compiled pattern
- See also:
- Companion:
- object
- Source:
- Regex.scala
Value members
Constructors
Compile a regular expression, supplied as a string, into a pattern that can be matched against inputs.
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"
Inline group names are preferred over group names supplied to the constructor when retrieving matched groups by name. Group names supplied to the constructor should be considered deprecated.
This constructor does not support options as flags, which must be
supplied as inline flags in the pattern string: (?idmsuxU)
.
- Value parameters:
- 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.
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 parameters:
- 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.
Return all non-overlapping matches of this regexp in given character sequence as a scala.collection.Iterator of scala.util.matching.Regex.Match.
- Value parameters:
- 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.
Return an optional first matching string of this Regex
in the given character sequence,
or None if there is no match.
- Value parameters:
- 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.
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 parameters:
- 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.
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 parameters:
- 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.
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 parameters:
- 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.
Returns whether this Regex
matches the given character sequence.
Like the extractor, this method takes anchoring into account.
- Value parameters:
- source
The text to match against
- Returns:
true if and only if
source
matches thisRegex
.- See also:
- Example:
"""\d+""".r matches "123" // returns true
- Source:
- Regex.scala
Replaces all matches by a 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 parameters:
- replacement
The string that will replace each match
- target
The string to match
- Returns:
The resulting string
- Example:
"""\d+""".r replaceAllIn ("July 15", "<NUMBER>") // returns "July <NUMBER>"
- Source:
- Regex.scala
Replaces all matches using a replacer function.
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 parameters:
- replacer
The function which maps a match to another string.
- target
The string to match.
- Returns:
The target string after replacements.
- Source:
- Regex.scala
Replaces the first match by a 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 parameters:
- replacement
The string that will replace the match
- target
The string to match
- Returns:
The resulting string
- Source:
- Regex.scala
Replaces some of the matches using a replacer function that returns an scala.Option.
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 parameters:
- 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
Splits the provided character sequence around matches of this regexp.
Splits the provided character sequence around matches of this regexp.
- Value parameters:
- toSplit
The character sequence to split
- Returns:
The array of strings computed by splitting the input around matches of this regexp
- Source:
- Regex.scala
The string defining the regular expression
The string defining the regular expression
- Definition Classes
- 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.
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.
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 parameters:
- s
The string to match
- Returns:
The matches
- Source:
- Regex.scala
Tries to match the String representation of a scala.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
- Value parameters:
- c
The Char to match
- Returns:
The match
- Source:
- Regex.scala
Tries to match on a scala.util.matching.Regex.Match.
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.
- Source:
- Regex.scala