From 63c7ca40d8320a5b4ecb373de69d65db49bc1122 Mon Sep 17 00:00:00 2001 From: naruse Date: Thu, 17 Sep 2009 00:40:49 +0000 Subject: * doc/re.rb: New document for Ruby's fork of Oniguruma. written by Run Paint Run Run [ruby-core:25420] * re.c: import document in doc/re.rb. * .document: add doc/re.rb. git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@24973 b2dd03c8-39d4-4d8f-98ff-823fe69b080e --- doc/re.rb | 584 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 584 insertions(+) create mode 100644 doc/re.rb (limited to 'doc') diff --git a/doc/re.rb b/doc/re.rb new file mode 100644 index 0000000000..6eabbb5c5a --- /dev/null +++ b/doc/re.rb @@ -0,0 +1,584 @@ +module Doc +# Regular expressions (regexps) are patterns which describe the +# contents of a string. They're used for testing whether a string contains a +# given pattern, or extracting the portions that match. They are created +# with the /pat/ and +# %r{pat} literals or the Regexp.new +# constructor. +# +# A regexp is usually delimited with forward slashes (/). For +# example: +# +# /hay/ =~ 'haystack' #=> 0 +# /y/.match('haystack') #=> # +# +# If a string contains the pattern it is said to match. A literal +# string matches itself. +# +# # 'haystack' does not contain the pattern 'needle', so doesn't match. +# /needle/.match('haystack') #=> nil +# # 'haystack' does contain the pattern 'hay', so it matches +# /hay/.match('haystack') #=> # +# +# Specifically, /st/ requires that the string contains the letter +# _s_ followed by the letter _t_, so it matches _haystack_, also. +# +# == Metacharacters and Escapes +# +# The following are metacharacters (, ), +# [, ], {, }, ., ?, +# +, *. They have a specific meaning when appearing in a +# pattern. To match them literally they must be backslash-escaped. To match +# a backslash literally backslash-escape that: \\\\\\. +# +# /1 \+ 2 = 3\?/.match('Does 1 + 2 = 3?') #=> # +# +# Patterns behave like double-quoted strings so can contain the same +# backslash escapes. +# +# /\s\u{6771 4eac 90fd}/.match("Go to 東京都") +# #=> # +# +# Arbitrary Ruby expressions can be embedded into patterns with the +# #{...} construct. +# +# place = "東京都" +# /#{place}/.match("Go to 東京都") +# #=> # +# +# == Character Classes +# +# A character class is delimited with square brackets ([, +# ]) and lists characters that may appear at that point in the +# match. /[ab]/ means _a_ or _b_, as opposed to /ab/ which +# means _a_ followed by _b_. +# +# /W[aeiou]rd/.match("Word") #=> # +# +# Within a character class the hyphen (-) is a metacharacter +# denoting an inclusive range of characters. [abcd] is equivalent +# to [a-d]. A range can be followed by another range, so +# [abcdwxyz] is equivalent to [a-dw-z]. The order in which +# ranges or individual characters appear inside a character class is +# irrelevant. +# +# /[0-9a-f]/.match('9f') #=> # +# /[9f]/.match('9f') #=> # +# +# If the first character of a character class is a caret (^) the +# class is inverted: it matches any character _except_ those named. +# +# /[^a-eg-z]/.match('f') #=> # +# +# A character class may contain another character class. By itself this +# isn't useful because [a-z[0-9]] describes the same set as +# [a-z0-9]. However, character classes also support the && +# operator which performs set intersection on its arguments. The two can be +# combined as follows: +# +# /[a-w&&[^c-g]z]/ # ([a-w] AND ([^c-g] OR z)) +# # This is equivalent to: +# /[abh-w]/ +# +# The following metacharacters also behave like character classes: +# +# * /./ - Any character except a newline. +# * /./m - Any character (the +m+ modifier enables multiline mode) +# * /\w/ - A word character ([a-zA-Z0-9_]) +# * /\W/ - A non-word character ([^a-zA-Z0-9_]) +# * /\d/ - A digit character ([0-9]) +# * /\D/ - A non-digit character ([^0-9]) +# * /\h/ - A hexdigit character ([0-9a-fA-F]) +# * /\H/ - A non-hexdigit character ([^0-9a-fA-F]) +# * /\s/ - A whitespace character: /[ \t\r\n\f]/ +# * /\S/ - A non-whitespace character: /[^ \t\r\n\f]/ +# +# POSIX bracket expressions are also similar to character classes. +# They provide a portable alternative to the above, with the added benefit +# that they encompass non-ASCII characters. For instance, /\d/ +# matches only the ASCII decimal digits (0-9); whereas /[[:digit:]]/ +# matches any character in the Unicode _Nd_ category. +# +# * /[[:alnum:]]/ - Alphabetic and numeric character +# * /[[:alpha:]]/ - Alphabetic character +# * /[[:blank:]]/ - Space or tab +# * /[[:cntrl:]]/ - Control character +# * /[[:digit:]]/ - Digit +# * /[[:graph:]]/ - Non-blank character (excludes spaces, control +# characters, and similar) +# * /[[:lower:]]/ - Lowercase alphabetical character +# * /[[:print:]]/ - Like [:graph:], but includes the space character +# * /[[:punct:]]/ - Punctuation character +# * /[[:space:]]/ - Whitespace character ([:blank:], newline, +# carriage return, etc.) +# * /[[:upper:]]/ - Uppercase alphabetical +# * /[[:xdigit:]]/ - Digit allowed in a hexadecimal number (i.e., +# 0-9a-fA-F) +# +# Ruby also supports the following non-POSIX character classes: +# +# * /[[:word:]]/ - A character in one of the following Unicode +# general categories _Letter_, _Mark_, _Number_, +# Connector_Punctuation +# * /[[:ascii:]]/ - A character in the ASCII character set +# +# # U+06F2 is "EXTENDED ARABIC-INDIC DIGIT TWO" +# /[[:digit:]]/.match("\u06F2") #=> # +# /[[:upper:]][[:lower:]]/.match("Hello") #=> # +# /[[:xdigit:]][[:xdigit:]]/.match("A6") #=> # +# +# == Repetition +# +# The constructs described so far match a single character. They can be +# followed by a repetition metacharacter to specify how many times they need +# to occur. Such metacharacters are called quantifiers. +# +# * * - Zero or more times +# * + - One or more times +# * ? - Zero or one times (optional) +# * {n} - Exactly n times +# * {n,} - n or more times +# * {,m} - m or less times +# * {n,m} - At least n and +# at most m times +# +# # At least one uppercase character ('H'), at least one lowercase +# # character ('e'), two 'l' characters, then one 'o' +# "Hello".match(/[[:upper:]]+[[:lower:]]+l{2}o/) #=> # +# +# Repetition is greedy by default: as many occurrences as possible +# are matched while still allowing the overall match to succeed. By +# contrast, lazy matching makes the minimal amount of matches +# necessary for overall success. A greedy metacharacter can be made lazy by +# following it with ?. +# +# # Both patterns below match the string. The fist uses a greedy +# # quantifier so '.+' matches ''; the second uses a lazy +# # quantifier so '.+?' matches ''. +# /<.+>/.match("") #=> #"> +# /<.+?>/.match("") #=> #"> +# +# A quantifier followed by + matches possessively: once it +# has matched it does not backtrack. They behave like greedy quantifiers, +# but having matched they refuse to "give up" their match even if this +# jeopardises the overall match. +# +# == Capturing +# +# Parentheses can be used for capturing. The text enclosed by the +# nth group of parentheses can be subsequently referred to +# with n. Within a pattern use the backreference +# \n; outside of the pattern use +# MatchData[n]. +# +# # 'at' is captured by the first group of parentheses, then referred to +# # later with \1 +# /[csh](..) [csh]\1 in/.match("The cat sat in the hat") +# #=> # +# # Regexp#match returns a MatchData object which makes the captured +# # text available with its #[] method. +# /[csh](..) [csh]\1 in/.match("The cat sat in the hat")[1] #=> 'at' +# +# Capture groups can be referred to by name when defined with the +# (?<name>) or (?'name') +# constructs. +# +# /\$(?\d+)\.(?\d+)/.match("$3.67") +# => # +# /\$(?\d+)\.(?\d+)/.match("$3.67")[:dollars] #=> "3" +# +# Named groups can be backreferenced with \k<name>, +# where _name_ is the group name. +# +# /(?[aeiou]).\k.\k/.match('ototomy') +# #=> # +# +# *Note*: A regexp can't use named backreferences and numbered +# backreferences simultaneously. +# +# When named capture groups are used with a literal regexp on the left-hand +# side of an expression and the =~ operator, the captured text is +# also assigned to local variables with corresponding names. +# +# /\$(?\d+)\.(?\d+)/ =~ "$3.67" #=> 0 +# dollars #=> "3" +# +# == Grouping +# +# Parentheses also group the terms they enclose, allowing them to be +# quantified as one atomic whole. +# +# # The pattern below matches a vowel followed by 2 word characters: +# # 'aen' +# /[aeiou]\w{2}/.match("Caenorhabditis elegans") #=> # +# # Whereas the following pattern matches a vowel followed by a word +# # character, twice, i.e. [aeiou]\w[aeiou]\w: 'enor'. +# /([aeiou]\w){2}/.match("Caenorhabditis elegans") +# #=> # +# +# The (?:...) construct provides grouping without +# capturing. That is, it combines the terms it contains into an atomic whole +# without creating a backreference. This benefits performance at the slight +# expense of readabilty. +# +# # The group of parentheses captures 'n' and the second 'ti'. The +# # second group is referred to later with the backreference \2 +# /I(n)ves(ti)ga\2ons/.match("Investigations") +# #=> # +# # The first group of parentheses is now made non-capturing with '?:', +# # so it still matches 'n', but doesn't create the backreference. Thus, +# # the backreference \1 now refers to 'ti'. +# /I(?:n)ves(ti)ga\1ons/.match("Investigations") +# #=> # +# +# === Atomic Grouping +# +# Grouping can be made atomic with +# (?>pat). This causes the subexpression pat +# to be matched independently of the rest of the expression such that what +# it matches becomes fixed for the remainder of the match, unless the entire +# subexpression must be abandoned and subsequently revisited. In this +# way pat is treated as a non-divisible whole. Atomic grouping is +# typically used to optimise patterns so as to prevent the regular +# expression engine from backtracking needlesly. +# +# # The " in the pattern below matches the first character of +# # the string, then .* matches Quote". This causes the +# # overall match to fail, so the text matched by .* is +# # backtracked by one position, which leaves the final character of the +# # string available to match " +# /".*"/.match('"Quote"') #=> # +# # If .* is grouped atomically, it refuses to backtrack +# # Quote", even though this means that the overall match fails +# /"(?>.*)"/.match('"Quote"') #=> nil +# +# == Subexpression Calls +# +# The \g<name> syntax matches the previous +# subexpression named _name_, which can be a group name or number, again. +# This differs from backreferences in that it re-executes the group rather +# than simply trying to re-match the same text. +# +# # Matches a ( character and assigns it to the paren +# # group, tries to call that the paren sub-expression again +# # but fails, then matches a literal ). +# /\A(?\(\g*\))*\z/ =~ '()' +# +# +# /\A(?\(\g*\))*\z/ =~ '(())' #=> 0 +# # ^1 +# # ^2 +# # ^3 +# # ^4 +# # ^5 +# # ^6 +# # ^7 +# # ^8 +# # ^9 +# # ^10 +# +# 1. Matches at the beginning of the string, i.e. before the first +# character. +# 2. Enters a named capture group called paren +# 3. Matches a literal (, the first character in the string +# 4. Calls the paren group again, i.e. recurses back to the +# second step +# 5. Re-enters the paren group +# 6. Matches a literal (, the second character in the +# string +# 7. Try to call paren a third time, but fail because +# doing so would prevent an overall successful match +# 8. Match a literal ), the third character in the string. +# Marks the end of the second recursive call +# 9. Match a literal ), the fourth character in the string +# 10. Match the end of the string +# +# == Alternation +# +# The vertical bar metacharacter (|) combines two expressions into +# a single one that matches either of the expressions. Each expression is an +# alternative. +# +# /\w(and|or)\w/.match("Feliformia") #=> # +# /\w(and|or)\w/.match("furandi") #=> # +# /\w(and|or)\w/.match("dissemblance") #=> nil +# +# == Character Properties +# +# The \p{} construct matches characters with the named property, +# much like POSIX bracket classes. +# +# * /\p{Alnum}/ - Alphabetic and numeric character +# * /\p{Alpha}/ - Alphabetic character +# * /\p{Blank}/ - Space or tab +# * /\p{Cntrl}/ - Control character +# * /\p{Digit}/ - Digit +# * /\p{Graph}/ - Non-blank character (excludes spaces, control +# characters, and similar) +# * /\p{Lower}/ - Lowercase alphabetical character +# * /\p{Print}/ - Like \p{Graph}, but includes the space character +# * /\p{Punct}/ - Punctuation character +# * /\p{Space}/ - Whitespace character ([:blank:], newline, +# carriage return, etc.) +# * /\p{Upper}/ - Uppercase alphabetical +# * /\p{XDigit}/ - Digit allowed in a hexadecimal number (i.e., 0-9a-fA-F) +# * /\p{Word}/ - A member of one of the following Unicode general +# category Letter, Mark, Number, +# Connector\_Punctuation +# * /\p{ASCII}/ - A character in the ASCII character set +# * /\p{Any}/ - Any Unicode character (including unassigned +# characters) +# * /\p{Assigned}/ - An assigned character +# +# A Unicode character's General Category value can also be matched +# with \p{Ab} where Ab is the category's +# abbreviation as described below: +# +# * /\p{L}/ - 'Letter' +# * /\p{Ll}/ - 'Letter: Lowercase' +# * /\p{Lm}/ - 'Letter: Mark' +# * /\p{Lo}/ - 'Letter: Other' +# * /\p{Lt}/ - 'Letter: Titlecase' +# * /\p{Lu}/ - 'Letter: Uppercase +# * /\p{Lo}/ - 'Letter: Other' +# * /\p{M}/ - 'Mark' +# * /\p{Mn}/ - 'Mark: Nonspacing' +# * /\p{Mc}/ - 'Mark: Spacing Combining' +# * /\p{Me}/ - 'Mark: Enclosing' +# * /\p{N}/ - 'Number' +# * /\p{Nd}/ - 'Number: Decimal Digit' +# * /\p{Nl}/ - 'Number: Letter' +# * /\p{No}/ - 'Number: Other' +# * /\p{P}/ - 'Punctuation' +# * /\p{Pc}/ - 'Punctuation: Connector' +# * /\p{Pd}/ - 'Punctuation: Dash' +# * /\p{Ps}/ - 'Punctuation: Open' +# * /\p{Pe}/ - 'Punctuation: Close' +# * /\p{Pi}/ - 'Punctuation: Initial Quote' +# * /\p{Pf}/ - 'Punctuation: Final Quote' +# * /\p{Po}/ - 'Punctuation: Other' +# * /\p{S}/ - 'Symbol' +# * /\p{Sm}/ - 'Symbol: Math' +# * /\p{Sc}/ - 'Symbol: Currency' +# * /\p{Sc}/ - 'Symbol: Currency' +# * /\p{Sk}/ - 'Symbol: Modifier' +# * /\p{So}/ - 'Symbol: Other' +# * /\p{Z}/ - 'Separator' +# * /\p{Zs}/ - 'Separator: Space' +# * /\p{Zl}/ - 'Separator: Line' +# * /\p{Zp}/ - 'Separator: Paragraph' +# * /\p{C}/ - 'Other' +# * /\p{Cc}/ - 'Other: Control' +# * /\p{Cf}/ - 'Other: Format' +# * /\p{Cn}/ - 'Other: Not Assigned' +# * /\p{Co}/ - 'Other: Private Use' +# * /\p{Cs}/ - 'Other: Surrogate' +# +# Lastly, \p{} matches a character's Unicode script. The +# following scripts are supported: Arabic, Armenian, +# Balinese, Bengali, Bopomofo, Braille, +# Buginese, Buhid, Canadian_Aboriginal, Carian, +# Cham, Cherokee, Common, Coptic, +# Cuneiform, Cypriot, Cyrillic, Deseret, +# Devanagari, Ethiopic, Georgian, Glagolitic, +# Gothic, Greek, Gujarati, Gurmukhi, Han, +# Hangul, Hanunoo, Hebrew, Hiragana, +# Inherited, Kannada, Katakana, Kayah_Li, +# Kharoshthi, Khmer, Lao, Latin, Lepcha, +# Limbu, Linear_B, Lycian, Lydian, +# Malayalam, Mongolian, Myanmar, New_Tai_Lue, +# Nko, Ogham, Ol_Chiki, Old_Italic, +# Old_Persian, Oriya, Osmanya, Phags_Pa, +# Phoenician, Rejang, Runic, Saurashtra, +# Shavian, Sinhala, Sundanese, Syloti_Nagri, +# Syriac, Tagalog, Tagbanwa, Tai_Le, +# Tamil, Telugu, Thaana, Thai, Tibetan, +# Tifinagh, Ugaritic, Vai, and Yi. +# +# # Unicode codepoint U+06E9 is named "ARABIC PLACE OF SAJDAH" and +# # belongs to the Arabic script. +# /\p{Arabic}/.match("\u06E9") #=> # +# +# All character properties can be inverted by prefixing their name with a +# caret (^). +# +# # Letter 'A' is not in the Unicode Ll (Letter; Lowercase) category, so +# # this match succeeds +# /\p{^Ll}/.match("A") #=> # +# +# == Anchors +# +# Anchors are metacharacter that match the zero-width positions between +# characters, anchoring the match to a specific position. +# +# * ^ - Matches beginning of line +# * $ - Matches end of line +# * \A - Matches beginning of string. +# * \Z - Matches end of string. If string ends with a newline, +# it matches just before newline +# * \z - Matches end of string +# * \G - Matches point where last match finished +# * \b - Matches word boundaries when outside brackets; backspace +# (0x08) inside brackets +# * \B - Matches non-word boundaries +# * (?=pat) - Positive lookahead assertion: +# ensures that the following characters match pat, but doesn't +# include those characters in the matched text +# * (?!pat) - Negative lookahead assertion: +# ensures that the following characters do not match pat, but +# doesn't include those characters in the matched text +# * (?<=pat) - Positive lookbehind +# assertion: ensures that the preceding characters match pat, but +# doesn't include those characters in the matched text +# * (?pat) - Negative lookbehind +# assertion: ensures that the preceding characters do not match +# pat, but doesn't include those characters in the matched text +# +# # If a pattern isn't anchored it can begin at any point in the string +# /real/.match("surrealist") #=> # +# # Anchoring the pattern to the beginning of the string forces the +# # match to start there. 'real' doesn't occur at the beginning of the +# # string, so now the match fails +# /\Areal/.match("surrealist") #=> nil +# # The match below fails because although 'Demand' contains 'and', the +# pattern does not occur at a word boundary. +# /\band/.match("Demand") +# # Whereas in the following example 'and' has been anchored to a +# # non-word boundary so instead of matching the first 'and' it matches +# # from the fourth letter of 'demand' instead +# /\Band.+/.match("Supply and demand curve") #=> # +# # The pattern below uses positive lookahead and positive lookbehind to +# # match text appearing in tags without including the tags in the +# # match +# /(?<=)\w+(?=<\/b>)/.match("Fortune favours the bold") +# #=> # +# +# == Options +# +# The end delimiter for a regexp can be followed by one or more single-letter +# options which control how the pattern can match. +# +# * /pat/i - Ignore case +# * /pat/m - Treat a newline as a character matched by . +# * /pat/x - Ignore whitespace and comments in the pattern +# * /pat/o - Perform #{} interpolation only once +# +# i, m, and x can also be applied on the +# subexpression level with the +# (?on-off) construct, which +# enables options on, and disables options off for the +# expression enclosed by the parentheses. +# +# /a(?i:b)c/.match('aBc') #=> # +# /a(?i:b)c/.match('abc') #=> # +# +# == Free-Spacing Mode and Comments +# +# As mentioned above, the x option enables free-spacing +# mode. Literal white space inside the pattern is ignored, and the +# octothorpe (#) character introduces a comment until the end of +# the line. This allows the components of the pattern to be organised in a +# potentially more readable fashion. +# +# # A contrived pattern to match a number with optional decimal places +# float_pat = /\A +# [[:digit:]]+ # 1 or more digits before the decimal point +# (\. # Decimal point +# [[:digit:]]+ # 1 or more digits after the decimal point +# )? # The decimal point and following digits are optional +# \Z/x +# float_pat.match('3.14') #=> # +# +# *Note*: To match whitespace in an x pattern use an escape such as +# \s or \p{Space}. +# +# Comments can be included in a non-x pattern with the +# (?#comment) construct, where comment is +# arbitrary text ignored by the regexp engine. +# +# == Encoding +# +# Regular expressions are assumed to use the source encoding. This can be +# overridden with one of the following modifiers. +# +# * /pat/u - UTF-8 +# * /pat/e - EUC-JP +# * /pat/s - Windows-31J +# * /pat/n - ASCII-8BIT +# +# A regexp can be matched against a string when they either share an +# encoding, or the regexp's encoding is _US-ASCII_ and the string's encoding +# is ASCII-compatible. +# +# If a match between incompatible encodings is attempted an +# Encoding::CompatibilityError exception is raised. +# +# The Regexp#fixed_encoding? predicate indicates whether the regexp +# has a fixed encoding, that is one incompatible with ASCII. A +# regexp's encoding can be explicitly fixed by supplying +# Regexp::FIXEDENCODING as the second argument of +# Regexp.new: +# +# r = Regexp.new("a".force_encoding("iso-8859-1"),Regexp::FIXEDENCODING) +# r =~"a\u3042" +# #=> Encoding::CompatibilityError: incompatible encoding regexp match +# (ISO-8859-1 regexp with UTF-8 string) +# +# == Performance +# +# Certain pathological combinations of constructs can lead to abysmally bad +# performance. +# +# Consider a string of 25 as, a d, 4 as, and a +# c. +# +# s = 'a' * 25 + 'd' 'a' * 4 + 'c' +# #=> "aaaaaaaaaaaaaaaaaaaaaaaaadadadadac" +# +# The following patterns match instantly as you would expect: +# +# /(b|a)/ =~ s #=> 0 +# /(b|a+)/ =~ s #=> 0 +# /(b|a+)*\/ =~ s #=> 0 +# +# However, the following pattern takes appreciably longer: +# +# /(b|a+)*c/ =~ s #=> 32 +# +# This happens because an atom in the regexp is quantified by both an +# immediate + and an enclosing * with nothing to +# differentiate which is in control of any particular character. The +# nondeterminism that results produces super-linear performance. (Consult +# Mastering Regular Expressions (3rd ed.), pp 222, by +# Jeffery Friedl, for an in-depth analysis). This particular case +# can be fixed by use of atomic grouping, which prevents the unnecessary +# backtracking: +# +# (start = Time.now) && /(b|a+)*c/ =~ s && (Time.now - start) +# #=> 24.702736882 +# (start = Time.now) && /(?>b|a+)*c/ =~ s && (Time.now - start) +# #=> 0.000166571 +# +# A similar case is typified by the following example, which takes +# approximately 60 seconds to execute for me: +# +# # Match a string of 29 as against a pattern of 29 optional +# # as followed by 29 mandatory as. +# Regexp.new('a?' * 29 + 'a' * 29) =~ 'a' * 29 +# +# The 29 optional as match the string, but this prevents the 29 +# mandatory as that follow from matching. Ruby must then backtrack +# repeatedly so as to satisfy as many of the optional matches as it can +# while still matching the mandatory 29. It is plain to us that none of the +# optional matches can succeed, but this fact unfortunately eludes Ruby. +# +# One approach for improving performance is to anchor the match to the +# beginning of the string, thus significantly reducing the amount of +# backtracking needed. +# +# Regexp.new('\A' 'a?' * 29 + 'a' * 29).match('a' * 29) +# #=> # +# +# + class Regexp; end +end -- cgit v1.2.3