Javascript String to Regex without Escaping

Question

I have a question regarding regular expressions in nodejs/javascript.

What I am trying to achieve is to convert a regex (loaded from a database as a string) without any escaping to a RegExp object in js.

var regex       = /Apache\/([0-9\.]+) \(([a-zA-Z ]+)\) (.+)/;
var regexString = '/Apache\/([0-9\.]+) \(([a-zA-Z ]+)\) (.+)/';

var str = 'Apache/2.2.9 (Debian) PHP/5.2.6-1+lenny18';

var match = str.match(regex);
var match2 = str.match(new RegExp(regexString));
console.log(match);
console.log(match2);

That's what I tried so far. But as you can see it won't match if the string gets escaped... My output:

[ 'Apache/2.2.9 (Debian) PHP/5.2.6-1+lenny18',
  '2.2.9',
  'Debian',
  'PHP/5.2.6-1+lenny18',
  index: 0,
  input: 'Apache/2.2.9 (Debian) PHP/5.2.6-1+lenny18' ]
null

Am I missing something simple? If not any suggestions for me? Thanks

trincot · Accepted Answer · 2017-04-01 23:04:44Z

2

The two bounding / are not supposed to be present when used in the string argument of new RegExp().

Also, when you would write the string as a literal (which I understand is not really your case, since you get the string from the DB), you need to escape any backslashes in that literal to \\:

var regex       = /Apache\/([0-9\.]+) \(([a-zA-Z ]+)\) (.+)/;
var regexString = 'Apache\/([0-9\.]+) \\(([a-zA-Z ]+)\\) (.+)';

var str = 'Apache/2.2.9 (Debian) PHP/5.2.6-1+lenny18';

var match = str.match(regex);
var match2 = str.match(new RegExp(regexString));
console.log(match);
console.log(match2);

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Apr 1, 2017 at 23:04

trincot

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