正则表达式：将一个单词与指定字符的刚出现一次匹配

Question

I want to detect words starting with $ but ignore words starting with $$ because I want to give the user a way to escape that character.

I have tried many things, but the nearer I got was this: [^\\$]\\$\\w+

It matches occurrences like The side bar $$includes a| $Cheatsheet|, full The side bar $$includes a| $Cheatsheet|, full with the white space at the beginning of the word $Cheatsheet included. It should match the word $Cheatsheet only, without the space.

How can I do it? Any ideas?

Answer 1

The regex you tried [^\\$]\\$\\w+ will match not a dollar sign followed by a dollar sign and one or more times a word character. That would match for example a$Cheatsheet or $Cheatsheet with a leading space. Note that you don't have to escape the dollar sign in the character class.

If negative lookbehinds are supported, to match a word that does not start with a dollar sign you could use:

(?<!\\$)\\$\\w+

Regex demo

Without a lookbehind you could match what you don't want and capture what you do want in a capturing group.

\\${2}\\w+|(\\$\\w+)

Regex demo

If the dollar sign can also not be in the middle of the word you could use:

\\S(?:\\$+\\w+)+\\$?|(\\$\\w+)

Regex demo

Answer 2

Since negative lookbehinds are NOT yet supported in all JavaScript engines ( https://github.com/tc39/proposal-regexp-lookbehind ), you can start with your regex and introduce a match group:

[^\$](\$\w+)

then, to exclude aaa$bbb , it is possible to use:

\s(\$\w+)

edit : and to match at the beginning or after punctuation:

(?:^|[^$\w])(\$\w+)

https://regex101.com/r/3cW5oY/2

Answer 3

You want to escape a $ with $ . That means, you need

/(?:^|[^$])(?:\${2})*\B(\$\w+)/g

See the regex demo .

Details

• (?:^|[^$]) - start of string or any char but $
• (?:\\${2})* - 0 or more repetitions of double dollar (this is required to avoid matching literal dollars)
• \\B - requires start of string or non-word char before the next $
• (\\$\\w+) - Group 1: a $ and then 1+ word chars.

JS demo:

 var s = "The $side bar $$includes a| $Cheatsheet|, $$$$full aaa$side"; var res = [], m; var rx = /(?:^|[^$])(?:\\${2})*\\B(\\$\\w+)/g; while(m=rx.exec(s)) { res.push(m[1]); } console.log(res);