如何在正则表达式中使用前瞻以匹配无字符？

Question

I've got a set of regex's within a function that are working rather well for me, but I've encountered a new pattern where they fail. This function fails when there are no more characters in the string. For example my function matches and replaces text in the following: " 1 m is equivalent to... " becomes " 1 meter is equivalent to... " However, it fails on: " There are 100 cm in 1 m "

I'm using AS3, which I believe has a regex engine nearly equivalent to JavaScript's. The current pattern is:

[0-9]+ m(?= )|[0-9]+m(?= )

I loop through a list of patterns and replacement strings, so it was easy to add another pattern to the list. I tried:

[0-9]+ m(?=)|[0-9]+m(?=)

And:

[0-9]+ m(?='')|[0-9]+m(?='')

And both failed. I'm missing a fundamental tidbit of knowledge. I believe I need to know how to say, "look-ahead and match when there are no other characters in the line"

Answer 1

You could simplify your expression by looking for a word boundary ( \\b ); something like this:

var regex = /(\d+)\s*m\b/;
regex.exec('1 m is equivalent to...'); // => ["1 m", "1"]
regex.exec('There are 100 cm in 1 m'); // => ["1 m", "1"]

Answer 2

'行中没有其他字符'相当于'在行尾'，所以只需使用$元字符

Answer 3

You're looking for a word boundry which is represented by the sequence \\b . You could use the expression /\\d+\\s*m\\b/

\d+  - one or more digits
\s*  - any number of spaces
m    - a literal 'm'
\b   - a word boundry