Develop Reference

Find a string surrounded by square brackets and *not* prefaced with a specific character

I would like to have a match with
[testing]
but not
![testing]
This is my query to grab a string surrounded by square brackets:
\[([^\]]+)\]
var match = /^[^!]*\[([^\]]+)\]/.exec(issueBody);
if (match)
{
$ISSUE_BODY.selectRange(match.index, match.index+match[0].length);
}
and it works marvelously.
However, I have spent a good half hour on http://regexr.com/ trying to skip strings with a "!" in front, and couldn't.
EDIT: I'm sorry guys I didn't realize that there were operations that could not be supported by specific interpreters. I am writing in Javascript and apparently lookbehind is not supported, I get this error:
Uncaught SyntaxError: Invalid regular expression:
/(?
Sorry for wasting time :\

You can use alternation:
(?:^|[^!])(\[[^\]]+\])
RegEx Demo
Here (?:^|[^!]) will match start of input OR any character that is NOT !
Code:
var re = /(?:^|[^!])(\[[^\]]+\])/gm;
var str = '![foobar123]\n[xyz789]';
while ((m = re.exec(str)) !== null)
console.log(m[1]);
Output:
[xyz789]

In Javascript, where lookbehinds are not supported, you can use:
^[^!]*\[([^\]]+)\]
(with the multiline flag to match every start of a line)
See it on regexr.com.
And here's a visualization from debuggex.com:

You can just use capturing:
var re = /(?:^|[^!])(\[[^[\]]*])/g;
var str = '[goodtesting] ![badtesting] ';
var m;
while ((m = re.exec(str)) !== null) {
document.getElementById("r").innerHTML += m[1] + "<br/>";
}
<div id="r"/>
The (?:^|[^!])(\[[^[\]]*]) regex matches the start of string or any character other than a ! (with a non-capturing group (?:^|[^!])) and matches and captures the substring enclosed with [ and ] that has no [ and ] inside (with (\[[^[\]]*])). When we need to get multiple matches, we need to use RegExp#exec() and access the captured groups using the indices (here, index 1).
Also, in JS, when you do not need to check what is after the match, just a lookbehind without a lookahead, you can use a reverse string technique (use a lookahead with the reversed string):
function revStr(s) {
return s.split('').reverse().join('');
}
var re = /][^[\]]*\[(?!!)/g; // Here, the regex pattern is reverse, too
var str = '![badtesting] [goodtesting]';
var m;
while ((m = re.exec(revStr(str))) !== null) { // We reverse a string here
document.getElementById("res").innerHTML += revStr(m[0]); // and the matched value here
}
<div id="res"/>
This is not possible with longer patterns but this one seems simple enough to go for it.

regular expressions- not including a character

I want to capture the value for name from query string with regular expression; I have done the folowing:
/name=(.*)/g
example: ?name=foo&bar=baz
But this grabs all string to the end; I know ^ is used for not; but I could not figure out the right syntax.
Thanks

If you want to use regex you can use a non greedy operator like this:
name=(.*?)&
Btw, you can also you another regex like this to cover more cases:
name=(.*?)(?:&|$)
Working demo
Javascript code:
var re = /name=(.*?)(?:&|$)/gm;
var str = 'example: ?name=foo&bar=baz\nexample: ?name=foo\nexample: ?bar=baz&name=foo';
var m;
while ((m = re.exec(str)) !== null) {
if (m.index === re.lastIndex) {
re.lastIndex++;
}
// View your result using the m-variable.
// eg m[0] etc.
}

You can try /name=([^&]+)/ if you only have one or use global modifier for more

regex look-behind: Invalid regular expression: /(?<=\.)\S+$/: Invalid group

I have the following regexp
(?<=\.)\S+$
used to extract the extension (whatever comes after the last dot) of a string. regex101.com seems to accept my regexp: the string extension is correctly matched. As soon as I move it into a javascript script and try to test it against a string I get this error:
Invalid regular expression: /(?<=\.)\S+$/: Invalid group
I get the same error also with regex101 auto generated code:
var re = /(?<=\.)\S+$/;
var str = 'test.txt';
var m;
if ((m = re.exec(str)) !== null) {
if (m.index === re.lastIndex) {
re.lastIndex++;
}
// View your result using the m-variable.
// eg m[0] etc.
}
see fiddle HERE
Any hint?

You cannot use look-behinds in JavaScript regex. There are some JavaScript look-behind workarounds, but they all have their own handicaps. To play it safe, use capturing groups. Here, the contents you need will be in the 2nd group:
(\.)([^.]+)$
Or, with just 1 capturing group (to increase performance):
\.([^.]+)$
Code:
var re = /\.([^.]+)$/;
var str = 'test.txt';
var m;
if ((m = re.exec(str)) !== null) {
if (m.index === re.lastIndex) {
re.lastIndex++;
}
alert(m[1]);
}

Due to babel-loader error
Replace var re = /(?<=\.)\S+$/; with var re = new RegExp("(?<=\\.)\\S+$");

How can i extract only the words end with number?

i am getting a info from back-end. i need to convert that in to multiple word, and to require to store in array. using regexp how to get that?
here is the word:
Enter Room/Area^_^Area 100#_#Enter Grid^_^Grid2#_#Enter Level / Building^_^Building1#_#Enter Drawing^_^Drawing1#_#Enter Spec section^_^Spec2#_#Enter BOQ^_^BOQ1#_#
the result should be :
["Area 100", "Grid2","Building1", "Drawing1", "Spec2", "BOQ1" ]
So simply i would like to pick the words which end with number. upto the special char ^.

\b[a-zA-Z0-9 ]+\d+\b
Try this.See demo.
https://regex101.com/r/wZ0iA3/6
var re = /\b[a-zA-Z0-9 ]+\d+\b/gi;
var str = 'Enter Room/Area^_^Area 100#_#Enter Grid^_^Grid2#_#Enter Level / Building^_^Building1#_#Enter Drawing^_^Drawing1#_#Enter Spec section^_^Spec2#_#Enter BOQ^_^BOQ1#_#';
var m;
while ((m = re.exec(str)) != null) {
if (m.index === re.lastIndex) {
re.lastIndex++;
}
// View your result using the m-variable.
// eg m[0] etc.
}

JavaScript return only regex from string

This might be pretty simple, but I am having a hard time with it. Consider the following code:
var string = 'testingT#$^%#$ESTING__--232'
string = string.match(/^\w*$/)
if (string != null)
{
string = string.join('')
string = string.toUpperCase()
}
$('#my-input').val(string)
What I want to do, is to strip all characters that aren't alphanumeric or underscore from string, and then transform that string to uppercase.
So far I did that, it works perfectly if I don't add any special characters, but when I add - or ^ to it, for example, it deletes everything from #my-input

You can do this in one step:
string = string.replace(/[^\w]/g, '').toUpperCase();
console.log(string); //=> "TESTINGTESTING__232"

var string = string.replace(/[^a-zA-Z_0-9]/g,'').toUpperCase()
Also, do you need unicode? My regex will only match a-z, and not åÉø for example.

You need use 'global' flag in regex and remove match restriction.
var str = 'testingT#$^%#$ESTING__--232';
str = str.match(/\w+/g);
if (str !== null)
{
str = str.join('');
str = str.toUpperCase();
}
$('#my-input').val(str);