Ruby gsub / regex修饰符？

Question

Where can I find the documentation on the modifiers for gsub ? \\a \\b \\c \\1 \\2 \\3 %a %b %c $1 $2 %3 etc.?

Specifically, I'm looking at this code... something.gsub(/%u/, unit) what's the %u ?

Answer 1

First off, %u is nothing special in ruby regex:

mixonic@pandora ~ $ irb
irb(main):001:0> '%u'.gsub(/%u/,'heyhey')
=> "heyhey"

The definitive documentation for Ruby 1.8 regex is in the Ruby Doc Bundle:

• http://ruby-doc.org/docs/ruby-doc-bundle/Manual/man-1.4/syntax.html#regexp

Strings delimited by slashes are regular expressions. The characters right after latter slash denotes the option to the regular expression. Option i means that regular expression is case insensitive. Option i means that regular expression does expression substitution only once at the first time it evaluated. Option x means extended regular expression, which means whitespaces and commens are allowd in the expression. Option p denotes POSIX mode, in which newlines are treated as normal character (matches with dots).

The %r/STRING/ is the another form of the regular expression.

 ^ beginning of a line or string $ end of a line or string . any character except newline \\w word character[0-9A-Za-z_] \\W non-word character \\s whitespace character[ \\t\\n\\r\\f] \\S non-whitespace character \\d digit, same as[0-9] \\D non-digit \\A beginning of a string \\Z end of a string, or before newline at the end \\z end of a string \\b word boundary(outside[]only) \\B non-word boundary \\b backspace(0x08)(inside[]only) [ ] any single character of set * 0 or more previous regular expression *? 0 or more previous regular expression(non greedy) + 1 or more previous regular expression +? 1 or more previous regular expression(non greedy) {m,n} at least m but most n previous regular expression {m,n}? at least m but most n previous regular expression(non greedy) ? 0 or 1 previous regular expression | alternation ( ) grouping regular expressions (?# ) comment (?: ) grouping without backreferences (?= ) zero-width positive look-ahead assertion (?! ) zero-width negative look-ahead assertion (?ix-ix) turns on (or off) `i' and `x' options within regular expression. 

These modifiers are localized inside an enclosing group (if any). (?ix-ix: ) turns on (or off) i' and x' options within this non-capturing group.

Backslash notation and expression substitution available in regular expressions.

Good luck!

Answer 2

Zenspider's Quickref contains a section explaining which escape sequences can be used in regexen and one listing the pseudo variables that get set by a regexp match. In the second argument to gsub you simply write the name of the variable with a backslash instead of a $ and it will be replaced with the value of that variable after applying the regexp. If you use a double quoted string, you need to use two backslashes.

When using the block-form of gsub you can simply use the variables directly. If you return a string containing eg \\1 from the block, that will not be replaced with $1. That only happens when using the two-argument form.

Answer 3

If you use block in sub/gsub you can access to the groups like that :

>> rx = /(ab(cd)ef)/
>> s = "-abcdef-abcdef"
>> s.gsub(rx) { $2 }
=> "cdgh-cdghi"

Answer 4

对于Ruby 1.9的Oniguruma有正则表达式的一个良好的文档在这里 。

Answer 5

gsub is also a string substitution function within the LUA language.

Within the LUA regex language %u represents the Upper Case character class. ie It will match all upper case letters. Similarly %l will match lower case.

LUA Regex Class Patterns