搜索子字符串 Searching for Substrings

问题 Problem

你想搜索一个字符串，获取该子字符串匹配的起始位置或匹配值。

You need to search for a substring, and return either the starting position of the match or the matching value itself.

方法 Solution

使用正则表达式有好几种方法来实现，有些是调用RegExp字面量或者对象的方法，有的是调用String对象上的。

There are several ways to accomplish this using regular expressions. Some methods are called on a RegExp pattern or object and some are called on String objects.

RegExp对象 RegExp objects

第一种方法是调用RegExp字面量或者对象上的test方法，这个test方法会返回一个布尔值： The first way is to call the test method on a RegExp pattern or object. The test method returns a boolean value:

match = /sample/.test("Sample text")
# => false

match = /sample/i.test("Sample text")
# => true

下一种方法是调用RegExp字面量或者对象的exec方法，这个方法会返回一个数组（包含了匹配信息）或者null；

The next way to is to call the exec method on a RegExp pattern or object. The exec method returns an array an array with the match information or null:

match = /s(amp)le/i.exec "Sample text"
# => [ 'Sample', 'amp', index: 0, input: 'Sample text' ]

match = /s(amp)le/.exec "Sample text"
# => null

String对象 String objects

match方法对一个给定的字符串与RegExp匹配。如果带有g标志，则返回一个包含了所有匹配的数组，否则只返回第一个匹配值，或者返回null，如果没有匹配的话。

The match method matches a given string with the RegExp. With ‘g’ flag returns an array containing the matches, without ‘g’ flag returns just the first match or if no match is found returns null.

"Watch out for the rock!".match(/r?or?/g)
# => [ 'o', 'or', 'ro' ]

"Watch out for the rock!".match(/r?or?/)
# => [ 'o', index: 6, input: 'Watch out for the rock!' ]

"Watch out for the rock!".match(/ror/)
# => null

search用来做RegExp和字符串的匹配，如果匹配到就返回匹配的起始位置，否则返回-1。

The search method matches RegExp with string and returns the index of the beginning of the match if found, -1 if not.

"Watch out for the rock!".search /for/
# => 10

"Watch out for the rock!".search /rof/
# => -1

讨论 Discussion

正则表达式是一种测试或者匹配字串的强大的方式。

Regular Expressions are a powerful way to test and match substrings.