Namespace: go.std.regexp

v1.0

Contents

• Summary
• Index
• Constants
• Variables
• Functions, Macros, and Special Forms
• Types

Summary

Provides a low-level interface to the regexp package.

Package regexp implements regular expression search.

The syntax of the regular expressions accepted is the same
general syntax used by Perl, Python, and other languages.
More precisely, it is the syntax accepted by RE2 and described at
https://golang.org/s/re2syntax, except for \C.
For an overview of the syntax, run
go doc regexp/syntax

The regexp implementation provided by this package is
guaranteed to run in time linear in the size of the input.
(This is a property not guaranteed by most open source
implementations of regular expressions.) For more information
about this property, see
https://swtch.com/~rsc/regexp/regexp1.html
or any book about automata theory.

All characters are UTF-8-encoded code points.
Following utf8.DecodeRune, each byte of an invalid UTF-8 sequence
is treated as if it encoded utf8.RuneError (U+FFFD).

There are 16 methods of Regexp that match a regular expression and identify
the matched text. Their names are matched by this regular expression:

Find(All)?(String)?(Submatch)?(Index)?

If 'All' is present, the routine matches successive non-overlapping
matches of the entire expression. Empty matches abutting a preceding
match are ignored. The return value is a slice containing the successive
return values of the corresponding non-'All' routine. These routines take
an extra integer argument, n. If n >= 0, the function returns at most n
matches/submatches; otherwise, it returns all of them.

If 'String' is present, the argument is a string; otherwise it is a slice
of bytes; return values are adjusted as appropriate.

If 'Submatch' is present, the return value is a slice identifying the
successive submatches of the expression. Submatches are matches of
parenthesized subexpressions (also known as capturing groups) within the
regular expression, numbered from left to right in order of opening
parenthesis. Submatch 0 is the match of the entire expression, submatch 1 is
the match of the first parenthesized subexpression, and so on.

If 'Index' is present, matches and submatches are identified by byte index
pairs within the input string: result[2*n:2*n+1] identifies the indexes of
the nth submatch. The pair for n==0 identifies the match of the entire
expression. If 'Index' is not present, the match is identified by the text
of the match/submatch. If an index is negative or text is nil, it means that
subexpression did not match any string in the input. For 'String' versions
an empty string means either no match or an empty match.

There is also a subset of the methods that can be applied to text read
from a RuneReader:

MatchReader, FindReaderIndex, FindReaderSubmatchIndex

This set may grow. Note that regular expression matches may need to
examine text beyond the text returned by a match, so the methods that
match text from a RuneReader may read arbitrarily far into the input
before returning.

(There are a few other methods that do not match this pattern.)

Index

• *Regexp
• Compile
• CompilePOSIX
• Match
• MatchReader
• MatchString
• MustCompile
• MustCompilePOSIX
• QuoteMeta
• Regexp
• arrayOfRegexp

Legend

Constant Variable Function Macro Special form Type GoVar Receiver/Method

Constants

Constants are variables with :const true in their metadata. Joker currently does not recognize them as special; as such, it allows redefining them or their values.

(None.)

Variables

(None.)

Functions, Macros, and Special Forms

• Compile

  Function v1.0

  (Compile expr)
  

  Compile parses a regular expression and returns, if successful,
  a Regexp object that can be used to match against text.
  
  When matching against text, the regexp returns a match that
  begins as early as possible in the input (leftmost), and among those
  it chooses the one that a backtracking search would have found first.
  This so-called leftmost-first matching is the same semantics
  that Perl, Python, and other implementations use, although this
  package implements it without the expense of backtracking.
  For POSIX leftmost-longest matching, see CompilePOSIX.
  
  Go input arguments: (expr string)
  
  Go returns: (*Regexp, error)
  
  Joker input arguments: [^String expr]
  
  Joker returns: [^*Regexp, ^Error]

• CompilePOSIX

  Function v1.0

  (CompilePOSIX expr)
  

  CompilePOSIX is like Compile but restricts the regular expression
  to POSIX ERE (egrep) syntax and changes the match semantics to
  leftmost-longest.
  
  That is, when matching against text, the regexp returns a match that
  begins as early as possible in the input (leftmost), and among those
  it chooses a match that is as long as possible.
  This so-called leftmost-longest matching is the same semantics
  that early regular expression implementations used and that POSIX
  specifies.
  
  However, there can be multiple leftmost-longest matches, with different
  submatch choices, and here this package diverges from POSIX.
  Among the possible leftmost-longest matches, this package chooses
  the one that a backtracking search would have found first, while POSIX
  specifies that the match be chosen to maximize the length of the first
  subexpression, then the second, and so on from left to right.
  The POSIX rule is computationally prohibitive and not even well-defined.
  See https://swtch.com/~rsc/regexp/regexp2.html#posix for details.
  
  Go input arguments: (expr string)
  
  Go returns: (*Regexp, error)
  
  Joker input arguments: [^String expr]
  
  Joker returns: [^*Regexp, ^Error]

• Match

  Function v1.0

  (Match pattern b)
  

  Match reports whether the byte slice b
  contains any match of the regular expression pattern.
  More complicated queries need to use Compile and the full Regexp interface.
  
  Go input arguments: (pattern string, b []byte)
  
  Go returns: (matched bool, err error)
  
  Joker input arguments: [^String pattern, ^arrayOfByte b]
  
  Joker returns: [^Boolean matched, ^Error err]

• MatchReader

  Function v1.0

  (MatchReader pattern r)
  

  MatchReader reports whether the text returned by the RuneReader
  contains any match of the regular expression pattern.
  More complicated queries need to use Compile and the full Regexp interface.
  
  Go input arguments: (pattern string, r io.RuneReader)
  
  Go returns: (matched bool, err error)
  
  Joker input arguments: [^String pattern, ^go.std.io/RuneReader r]
  
  Joker returns: [^Boolean matched, ^Error err]

• MatchString

  Function v1.0

  (MatchString pattern s)
  

  MatchString reports whether the string s
  contains any match of the regular expression pattern.
  More complicated queries need to use Compile and the full Regexp interface.
  
  Go input arguments: (pattern string, s string)
  
  Go returns: (matched bool, err error)
  
  Joker input arguments: [^String pattern, ^String s]
  
  Joker returns: [^Boolean matched, ^Error err]

• MustCompile

  Function v1.0

  (MustCompile str)
  

  MustCompile is like Compile but panics if the expression cannot be parsed.
  It simplifies safe initialization of global variables holding compiled regular
  expressions.
  
  Go input arguments: (str string)
  
  Go returns: *Regexp
  
  Joker input arguments: [^String str]
  
  Joker returns: ^*Regexp

• MustCompilePOSIX

  Function v1.0

  (MustCompilePOSIX str)
  

  MustCompilePOSIX is like CompilePOSIX but panics if the expression cannot be parsed.
  It simplifies safe initialization of global variables holding compiled regular
  expressions.
  
  Go input arguments: (str string)
  
  Go returns: *Regexp
  
  Joker input arguments: [^String str]
  
  Joker returns: ^*Regexp

• QuoteMeta

  Function v1.0

  (QuoteMeta s)
  

  QuoteMeta returns a string that escapes all regular expression metacharacters
  inside the argument text; the returned string is a regular expression matching
  the literal text.
  
  Go input arguments: (s string)
  
  Go returns: string
  
  Joker input arguments: [^String s]
  
  Joker returns: ^String

Types

• *Regexp

  Concrete Type v1.0

  Regexp is the representation of a compiled regular expression.
  A Regexp is safe for concurrent use by multiple goroutines,
  except for configuration methods, such as Longest.
  

• Copy

  Receiver for *Regexp v1.0

  ([])
  

  Copy returns a new Regexp object copied from re.
  Calling Longest on one copy does not affect another.
  
  Deprecated: In earlier releases, when using a Regexp in multiple goroutines,
  giving each goroutine its own copy helped to avoid lock contention.
  As of Go 1.12, using Copy is no longer necessary to avoid lock contention.
  Copy may still be appropriate if the reason for its use is to make
  two copies with different Longest settings.
  

• Expand

  Receiver for *Regexp v1.0

  ([dst template src match])
  

  Expand appends template to dst and returns the result; during the
  append, Expand replaces variables in the template with corresponding
  matches drawn from src. The match slice should have been returned by
  FindSubmatchIndex.
  
  In the template, a variable is denoted by a substring of the form
  $name or ${name}, where name is a non-empty sequence of letters,
  digits, and underscores. A purely numeric name like $1 refers to
  the submatch with the corresponding index; other names refer to
  capturing parentheses named with the (?P<name>...) syntax. A
  reference to an out of range or unmatched index or a name that is not
  present in the regular expression is replaced with an empty slice.
  
  In the $name form, name is taken to be as long as possible: $1x is
  equivalent to ${1x}, not ${1}x, and, $10 is equivalent to ${10}, not ${1}0.
  
  To insert a literal $ in the output, use $$ in the template.
  

• ExpandString

  Receiver for *Regexp v1.0

  ([dst template src match])
  

  ExpandString is like Expand but the template and source are strings.
  It appends to and returns a byte slice in order to give the calling
  code control over allocation.
  

• Find

  Receiver for *Regexp v1.0

  ([b])
  

  Find returns a slice holding the text of the leftmost match in b of the regular expression.
  A return value of nil indicates no match.
  

• FindAll

  Receiver for *Regexp v1.0

  ([b n])
  

  FindAll is the 'All' version of Find; it returns a slice of all successive
  matches of the expression, as defined by the 'All' description in the
  package comment.
  A return value of nil indicates no match.
  

• FindAllIndex

  Receiver for *Regexp v1.0

  ([b n])
  

  FindAllIndex is the 'All' version of FindIndex; it returns a slice of all
  successive matches of the expression, as defined by the 'All' description
  in the package comment.
  A return value of nil indicates no match.
  

• FindAllString

  Receiver for *Regexp v1.0

  ([s n])
  

  FindAllString is the 'All' version of FindString; it returns a slice of all
  successive matches of the expression, as defined by the 'All' description
  in the package comment.
  A return value of nil indicates no match.
  

• FindAllStringIndex

  Receiver for *Regexp v1.0

  ([s n])
  

  FindAllStringIndex is the 'All' version of FindStringIndex; it returns a
  slice of all successive matches of the expression, as defined by the 'All'
  description in the package comment.
  A return value of nil indicates no match.
  

• FindAllStringSubmatch

  Receiver for *Regexp v1.0

  ([s n])
  

  FindAllStringSubmatch is the 'All' version of FindStringSubmatch; it
  returns a slice of all successive matches of the expression, as defined by
  the 'All' description in the package comment.
  A return value of nil indicates no match.
  

• FindAllStringSubmatchIndex

  Receiver for *Regexp v1.0

  ([s n])
  

  FindAllStringSubmatchIndex is the 'All' version of
  FindStringSubmatchIndex; it returns a slice of all successive matches of
  the expression, as defined by the 'All' description in the package
  comment.
  A return value of nil indicates no match.
  

• FindAllSubmatch

  Receiver for *Regexp v1.0

  ([b n])
  

  FindAllSubmatch is the 'All' version of FindSubmatch; it returns a slice
  of all successive matches of the expression, as defined by the 'All'
  description in the package comment.
  A return value of nil indicates no match.
  

• FindAllSubmatchIndex

  Receiver for *Regexp v1.0

  ([b n])
  

  FindAllSubmatchIndex is the 'All' version of FindSubmatchIndex; it returns
  a slice of all successive matches of the expression, as defined by the
  'All' description in the package comment.
  A return value of nil indicates no match.
  

• FindIndex

  Receiver for *Regexp v1.0

  ([b])
  

  FindIndex returns a two-element slice of integers defining the location of
  the leftmost match in b of the regular expression. The match itself is at
  b[loc[0]:loc[1]].
  A return value of nil indicates no match.
  

• FindReaderIndex

  Receiver for *Regexp v1.0

  ([r])
  

  FindReaderIndex returns a two-element slice of integers defining the
  location of the leftmost match of the regular expression in text read from
  the RuneReader. The match text was found in the input stream at
  byte offset loc[0] through loc[1]-1.
  A return value of nil indicates no match.
  

• FindReaderSubmatchIndex

  Receiver for *Regexp v1.0

  ([r])
  

  FindReaderSubmatchIndex returns a slice holding the index pairs
  identifying the leftmost match of the regular expression of text read by
  the RuneReader, and the matches, if any, of its subexpressions, as defined
  by the 'Submatch' and 'Index' descriptions in the package comment. A
  return value of nil indicates no match.
  

• FindString

  Receiver for *Regexp v1.0

  ([s])
  

  FindString returns a string holding the text of the leftmost match in s of the regular
  expression. If there is no match, the return value is an empty string,
  but it will also be empty if the regular expression successfully matches
  an empty string. Use FindStringIndex or FindStringSubmatch if it is
  necessary to distinguish these cases.
  

• FindStringIndex

  Receiver for *Regexp v1.0

  ([s])
  

  FindStringIndex returns a two-element slice of integers defining the
  location of the leftmost match in s of the regular expression. The match
  itself is at s[loc[0]:loc[1]].
  A return value of nil indicates no match.
  

• FindStringSubmatch

  Receiver for *Regexp v1.0

  ([s])
  

  FindStringSubmatch returns a slice of strings holding the text of the
  leftmost match of the regular expression in s and the matches, if any, of
  its subexpressions, as defined by the 'Submatch' description in the
  package comment.
  A return value of nil indicates no match.
  

• FindStringSubmatchIndex

  Receiver for *Regexp v1.0

  ([s])
  

  FindStringSubmatchIndex returns a slice holding the index pairs
  identifying the leftmost match of the regular expression in s and the
  matches, if any, of its subexpressions, as defined by the 'Submatch' and
  'Index' descriptions in the package comment.
  A return value of nil indicates no match.
  

• FindSubmatch

  Receiver for *Regexp v1.0

  ([b])
  

  FindSubmatch returns a slice of slices holding the text of the leftmost
  match of the regular expression in b and the matches, if any, of its
  subexpressions, as defined by the 'Submatch' descriptions in the package
  comment.
  A return value of nil indicates no match.
  

• FindSubmatchIndex

  Receiver for *Regexp v1.0

  ([b])
  

  FindSubmatchIndex returns a slice holding the index pairs identifying the
  leftmost match of the regular expression in b and the matches, if any, of
  its subexpressions, as defined by the 'Submatch' and 'Index' descriptions
  in the package comment.
  A return value of nil indicates no match.
  

• LiteralPrefix

  Receiver for *Regexp v1.0

  ([])
  

  LiteralPrefix returns a literal string that must begin any match
  of the regular expression re. It returns the boolean true if the
  literal string comprises the entire regular expression.
  

• Longest

  Receiver for *Regexp v1.0

  ([])
  

  Longest makes future searches prefer the leftmost-longest match.
  That is, when matching against text, the regexp returns a match that
  begins as early as possible in the input (leftmost), and among those
  it chooses a match that is as long as possible.
  This method modifies the Regexp and may not be called concurrently
  with any other methods.
  

• Match

  Receiver for *Regexp v1.0

  ([b])
  

  Match reports whether the byte slice b
  contains any match of the regular expression re.
  

• MatchReader

  Receiver for *Regexp v1.0

  ([r])
  

  MatchReader reports whether the text returned by the RuneReader
  contains any match of the regular expression re.
  

• MatchString

  Receiver for *Regexp v1.0

  ([s])
  

  MatchString reports whether the string s
  contains any match of the regular expression re.
  

• NumSubexp

  Receiver for *Regexp v1.0

  ([])
  

  NumSubexp returns the number of parenthesized subexpressions in this Regexp.
  

• ReplaceAll

  Receiver for *Regexp v1.0

  ([src repl])
  

  ReplaceAll returns a copy of src, replacing matches of the Regexp
  with the replacement text repl. Inside repl, $ signs are interpreted as
  in Expand, so for instance $1 represents the text of the first submatch.
  

• ReplaceAllLiteral

  Receiver for *Regexp v1.0

  ([src repl])
  

  ReplaceAllLiteral returns a copy of src, replacing matches of the Regexp
  with the replacement bytes repl. The replacement repl is substituted directly,
  without using Expand.
  

• ReplaceAllLiteralString

  Receiver for *Regexp v1.0

  ([src repl])
  

  ReplaceAllLiteralString returns a copy of src, replacing matches of the Regexp
  with the replacement string repl. The replacement repl is substituted directly,
  without using Expand.
  

• ReplaceAllString

  Receiver for *Regexp v1.0

  ([src repl])
  

  ReplaceAllString returns a copy of src, replacing matches of the Regexp
  with the replacement string repl. Inside repl, $ signs are interpreted as
  in Expand, so for instance $1 represents the text of the first submatch.
  

• Split

  Receiver for *Regexp v1.0

  ([s n])
  

  Split slices s into substrings separated by the expression and returns a slice of
  the substrings between those expression matches.
  
  The slice returned by this method consists of all the substrings of s
  not contained in the slice returned by FindAllString. When called on an expression
  that contains no metacharacters, it is equivalent to strings.SplitN.
  
  Example:
  s := regexp.MustCompile("a*").Split("abaabaccadaaae", 5)
  // s: ["", "b", "b", "c", "cadaaae"]
  
  The count determines the number of substrings to return:
  n > 0: at most n substrings; the last substring will be the unsplit remainder.
  n == 0: the result is nil (zero substrings)
  n < 0: all substrings
  

• String

  Receiver for *Regexp v1.0

  ([])
  

  String returns the source text used to compile the regular expression.
  

• SubexpIndex

  Receiver for *Regexp v1.0

  ([name])
  

  SubexpIndex returns the index of the first subexpression with the given name,
  or -1 if there is no subexpression with that name.
  
  Note that multiple subexpressions can be written using the same name, as in
  (?P<bob>a+)(?P<bob>b+), which declares two subexpressions named "bob".
  In this case, SubexpIndex returns the index of the leftmost such subexpression
  in the regular expression.
  

• SubexpNames

  Receiver for *Regexp v1.0

  ([])
  

  SubexpNames returns the names of the parenthesized subexpressions
  in this Regexp. The name for the first sub-expression is names[1],
  so that if m is a match slice, the name for m[i] is SubexpNames()[i].
  Since the Regexp as a whole cannot be named, names[0] is always
  the empty string. The slice should not be modified.
  

• Regexp

  Concrete Type v1.0

  Regexp is the representation of a compiled regular expression.
  A Regexp is safe for concurrent use by multiple goroutines,
  except for configuration methods, such as Longest.
  

• arrayOfRegexp

  Concrete Type v1.0

  Regexp is the representation of a compiled regular expression.
  A Regexp is safe for concurrent use by multiple goroutines,
  except for configuration methods, such as Longest.