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* doc/regexp.rdoc: [DOC] Replace paragraphs in verbatim sections with
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@ -1,3 +1,8 @@
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Tue Sep 17 12:55:58 2013 Eric Hodel <drbrain@segment7.net>
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* doc/regexp.rdoc: [DOC] Replace paragraphs in verbatim sections with
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plain paragraphs to improve readability as ri and HTML.
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Mon Sep 16 07:32:35 2013 Tadayoshi Funaba <tadf@dotrb.org>
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* complex.c: removed meaningless lines.
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132
doc/regexp.rdoc
132
doc/regexp.rdoc
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@ -16,9 +16,12 @@ example:
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If a string contains the pattern it is said to <i>match</i>. A literal
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string matches itself.
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# 'haystack' does not contain the pattern 'needle', so doesn't match.
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Here 'haystack' does not contain the pattern 'needle', so it doesn't match:
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/needle/.match('haystack') #=> nil
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# 'haystack' does contain the pattern 'hay', so it matches
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Here 'haystack' contains the pattern 'hay', so it matches:
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/hay/.match('haystack') #=> #<MatchData "hay">
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Specifically, <tt>/st/</tt> requires that the string contains the letter
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@ -50,7 +53,7 @@ object. Regexp.last_match is equivalent to <tt>$~</tt>.
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=== Regexp#match method
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#match method return a MatchData object :
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The #match method returns a MatchData object:
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/st/.match('haystack') #=> #<MatchData "st">
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@ -108,7 +111,9 @@ operator which performs set intersection on its arguments. The two can be
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combined as follows:
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/[a-w&&[^c-g]z]/ # ([a-w] AND ([^c-g] OR z))
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# This is equivalent to:
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This is equivalent to:
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/[abh-w]/
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The following metacharacters also behave like character classes:
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@ -173,8 +178,9 @@ to occur. Such metacharacters are called <i>quantifiers</i>.
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* <tt>{</tt><i>n</i><tt>,</tt><i>m</i><tt>}</tt> - At least <i>n</i> and
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at most <i>m</i> times
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# At least one uppercase character ('H'), at least one lowercase
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# character ('e'), two 'l' characters, then one 'o'
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At least one uppercase character ('H'), at least one lowercase character
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('e'), two 'l' characters, then one 'o':
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"Hello".match(/[[:upper:]]+[[:lower:]]+l{2}o/) #=> #<MatchData "Hello">
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Repetition is <i>greedy</i> by default: as many occurrences as possible
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@ -183,9 +189,10 @@ contrast, <i>lazy</i> matching makes the minimal amount of matches
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necessary for overall success. A greedy metacharacter can be made lazy by
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following it with <tt>?</tt>.
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# Both patterns below match the string. The first uses a greedy
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# quantifier so '.+' matches '<a><b>'; the second uses a lazy
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# quantifier so '.+?' matches '<a>'.
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Both patterns below match the string. The first uses a greedy quantifier so
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'.+' matches '<a><b>'; the second uses a lazy quantifier so '.+?' matches
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'<a>':
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/<.+>/.match("<a><b>") #=> #<MatchData "<a><b>">
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/<.+?>/.match("<a><b>") #=> #<MatchData "<a>">
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@ -202,12 +209,15 @@ with <i>n</i>. Within a pattern use the <i>backreference</i>
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<tt>\n</tt>; outside of the pattern use
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<tt>MatchData[</tt><i>n</i><tt>]</tt>.
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# 'at' is captured by the first group of parentheses, then referred to
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# later with \1
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'at' is captured by the first group of parentheses, then referred to later
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with <tt>\1</tt>:
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/[csh](..) [csh]\1 in/.match("The cat sat in the hat")
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#=> #<MatchData "cat sat in" 1:"at">
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# Regexp#match returns a MatchData object which makes the captured
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# text available with its #[] method.
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Regexp#match returns a MatchData object which makes the captured text
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available with its #[] method:
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/[csh](..) [csh]\1 in/.match("The cat sat in the hat")[1] #=> 'at'
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Capture groups can be referred to by name when defined with the
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@ -239,11 +249,13 @@ also assigned to local variables with corresponding names.
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Parentheses also <i>group</i> the terms they enclose, allowing them to be
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quantified as one <i>atomic</i> whole.
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# The pattern below matches a vowel followed by 2 word characters:
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# 'aen'
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The pattern below matches a vowel followed by 2 word characters:
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/[aeiou]\w{2}/.match("Caenorhabditis elegans") #=> #<MatchData "aen">
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# Whereas the following pattern matches a vowel followed by a word
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# character, twice, i.e. <tt>[aeiou]\w[aeiou]\w</tt>: 'enor'.
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Whereas the following pattern matches a vowel followed by a word character,
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twice, i.e. <tt>[aeiou]\w[aeiou]\w</tt>: 'enor'.
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/([aeiou]\w){2}/.match("Caenorhabditis elegans")
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#=> #<MatchData "enor" 1:"or">
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@ -252,13 +264,16 @@ capturing. That is, it combines the terms it contains into an atomic whole
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without creating a backreference. This benefits performance at the slight
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expense of readability.
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# The group of parentheses captures 'n' and the second 'ti'. The
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# second group is referred to later with the backreference \2
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The first group of parentheses captures 'n' and the second 'ti'. The second
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group is referred to later with the backreference <tt>\2</tt>:
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/I(n)ves(ti)ga\2ons/.match("Investigations")
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#=> #<MatchData "Investigations" 1:"n" 2:"ti">
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# The first group of parentheses is now made non-capturing with '?:',
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# so it still matches 'n', but doesn't create the backreference. Thus,
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# the backreference \1 now refers to 'ti'.
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The first group of parentheses is now made non-capturing with '?:', so it
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still matches 'n', but doesn't create the backreference. Thus, the
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backreference <tt>\1</tt> now refers to 'ti'.
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/I(?:n)ves(ti)ga\1ons/.match("Investigations")
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#=> #<MatchData "Investigations" 1:"ti">
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@ -273,14 +288,16 @@ way <i>pat</i> is treated as a non-divisible whole. Atomic grouping is
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typically used to optimise patterns so as to prevent the regular
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expression engine from backtracking needlessly.
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# The <tt>"</tt> in the pattern below matches the first character of
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# the string, then <tt>.*</tt> matches <i>Quote"</i>. This causes the
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# overall match to fail, so the text matched by <tt>.*</tt> is
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# backtracked by one position, which leaves the final character of the
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# string available to match <tt>"</tt>
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The <tt>"</tt> in the pattern below matches the first character of the string,
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then <tt>.*</tt> matches <i>Quote"</i>. This causes the overall match to fail,
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so the text matched by <tt>.*</tt> is backtracked by one position, which
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leaves the final character of the string available to match <tt>"</tt>
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/".*"/.match('"Quote"') #=> #<MatchData "\"Quote\"">
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# If <tt>.*</tt> is grouped atomically, it refuses to backtrack
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# <i>Quote"</i>, even though this means that the overall match fails
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If <tt>.*</tt> is grouped atomically, it refuses to backtrack <i>Quote"</i>,
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even though this means that the overall match fails
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/"(?>.*)"/.match('"Quote"') #=> nil
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== Subexpression Calls
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@ -290,9 +307,10 @@ subexpression named _name_, which can be a group name or number, again.
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This differs from backreferences in that it re-executes the group rather
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than simply trying to re-match the same text.
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# Matches a <i>(</i> character and assigns it to the <tt>paren</tt>
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# group, tries to call that the <tt>paren</tt> sub-expression again
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# but fails, then matches a literal <i>)</i>.
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This pattern matches a <i>(</i> character and assigns it to the <tt>paren</tt>
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group, tries to call that the <tt>paren</tt> sub-expression again but fails,
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then matches a literal <i>)</i>:
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/\A(?<paren>\(\g<paren>*\))*\z/ =~ '()'
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@ -426,15 +444,17 @@ following scripts are supported: <i>Arabic</i>, <i>Armenian</i>,
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<i>Tamil</i>, <i>Telugu</i>, <i>Thaana</i>, <i>Thai</i>, <i>Tibetan</i>,
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<i>Tifinagh</i>, <i>Ugaritic</i>, <i>Vai</i>, and <i>Yi</i>.
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# Unicode codepoint U+06E9 is named "ARABIC PLACE OF SAJDAH" and
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# belongs to the Arabic script.
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Unicode codepoint U+06E9 is named "ARABIC PLACE OF SAJDAH" and belongs to the
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Arabic script:
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/\p{Arabic}/.match("\u06E9") #=> #<MatchData "\u06E9">
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All character properties can be inverted by prefixing their name with a
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caret (<tt>^</tt>).
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# Letter 'A' is not in the Unicode Ll (Letter; Lowercase) category, so
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# this match succeeds
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Letter 'A' is not in the Unicode Ll (Letter; Lowercase) category, so this
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match succeeds:
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/\p{^Ll}/.match("A") #=> #<MatchData "A">
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== Anchors
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@ -465,22 +485,30 @@ characters, <i>anchoring</i> the match to a specific position.
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assertion: ensures that the preceding characters do not match
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<i>pat</i>, but doesn't include those characters in the matched text
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# If a pattern isn't anchored it can begin at any point in the string
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If a pattern isn't anchored it can begin at any point in the string:
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/real/.match("surrealist") #=> #<MatchData "real">
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# Anchoring the pattern to the beginning of the string forces the
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# match to start there. 'real' doesn't occur at the beginning of the
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# string, so now the match fails
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Anchoring the pattern to the beginning of the string forces the match to start
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there. 'real' doesn't occur at the beginning of the string, so now the match
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fails:
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/\Areal/.match("surrealist") #=> nil
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# The match below fails because although 'Demand' contains 'and', the
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pattern does not occur at a word boundary.
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The match below fails because although 'Demand' contains 'and', the pattern
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does not occur at a word boundary.
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/\band/.match("Demand")
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# Whereas in the following example 'and' has been anchored to a
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# non-word boundary so instead of matching the first 'and' it matches
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# from the fourth letter of 'demand' instead
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Whereas in the following example 'and' has been anchored to a non-word
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boundary so instead of matching the first 'and' it matches from the fourth
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letter of 'demand' instead:
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/\Band.+/.match("Supply and demand curve") #=> #<MatchData "and curve">
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# The pattern below uses positive lookahead and positive lookbehind to
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# match text appearing in <b></b> tags without including the tags in the
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# match
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The pattern below uses positive lookahead and positive lookbehind to match
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text appearing in <b></b> tags without including the tags in the match:
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/(?<=<b>)\w+(?=<\/b>)/.match("Fortune favours the <b>bold</b>")
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#=> #<MatchData "bold">
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@ -518,7 +546,8 @@ octothorpe (<tt>#</tt>) character introduces a comment until the end of
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the line. This allows the components of the pattern to be organised in a
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potentially more readable fashion.
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# A contrived pattern to match a number with optional decimal places
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A contrived pattern to match a number with optional decimal places:
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float_pat = /\A
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[[:digit:]]+ # 1 or more digits before the decimal point
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(\. # Decimal point
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@ -634,8 +663,9 @@ backtracking:
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A similar case is typified by the following example, which takes
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approximately 60 seconds to execute for me:
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# Match a string of 29 <i>a</i>s against a pattern of 29 optional
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# <i>a</i>s followed by 29 mandatory <i>a</i>s.
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Match a string of 29 <i>a</i>s against a pattern of 29 optional <i>a</i>s
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followed by 29 mandatory <i>a</i>s:
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Regexp.new('a?' * 29 + 'a' * 29) =~ 'a' * 29
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The 29 optional <i>a</i>s match the string, but this prevents the 29
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