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Replace string between second set of [ and ]

I am learning regex, and I got a doubt. Let's consider
var s = "YYYN[1-20]N[]NYY";
Now, I want to replace/insert the '1-8' between [ and ] at its second occurrence.
Then output should be
YYYN[1-20]N[1-8]NYY
For that I had tried using replace and passing a function through it as shown below:
var nth = 0;
s = s.replace(/\[([^)]+)\]/g, function(match, i, original) {
nth++;
return (nth === 1) ? "1-8" : match;
});
alert(s); // But It wont work
I think that regex is not matchIing the string that I am using.
How can I fix it?

You regex \[([^)]+)\] will not match empty square brackets since + requires at least 1 character other than ). I guess you wanted to write \[[^\]]*\].
Here is a fix for your solution:
var s = "YYYN[1-20]N[]NYY";
var nth = 0;
s = s.replace(/\[[^\]]*\]/g, function (match, i, original) {
nth++;
return (nth !== 1) ? "[1-8]" : match;
});
alert(s);
Here is another way of doing it:
var s = "YYYN[1-20]N[]NYY";
var nth = 0;
s = s.replace(/(.*)\[\]/, "$1[1-8]");
alert(s);
The regex (.*)\[\] matches and captures into Group 1 greedily as much text as possible (thus we get the last set of empty []), and then matches empty square brackets. Then we restore the text before [] with $1 backreference and add out string 1-8.

If it’s only two occurences of square brackets, then this will work:
/(.*\[.*?\].*\[).*?(\].*)/
This RegEx has “YYYN[1-20]N[” as the first capturing group and “]NYY” as the second.

I suggest using simple split and join operations:
var s = "YYYN[1-20]N[]NYY";
var arr = s.split(/\[/)
arr[2] = '1-8' + arr[2]
var r = arr.join('[')
//=> YYYN[1-20]N[1-8]NYY

You can use following regex :
var s = "YYYN[1-20]N[]NYY";
var nth = 0;
s = s.replace(/([^[]+\[(?:[^[]+)\][^[]+)\[[^[]+\](.+)/, "$1[1-8]$2");
alert(s);
The first part ([^[]+\[([^[]+)\][^[]+) will match a string contain first sub-string between []. and \[[^[]+\] would be the second one which you want and the last part (.+?) match the rest of your string.

split string based on a symbol

I'm trying to split a string into an array based on the second occurrence of the symbol _
var string = "this_is_my_string";
I want to split the string after the second underscore. The string is not always the same but it always has 2 or more underscores in it. I always need it split on the second underscore.
In the example string above I would need it to be split like this.
var split = [this_is, _my_string];

var string = "this_is_my_string";
var firstUnderscore = string.indexOf('_');
var secondUnderscore = string.indexOf('_', firstUnderscore + 1);
var split = [string.substring(0, secondUnderscore),
string.substring(secondUnderscore)];
Paste it into your browser's console to try it out. No need for a jsFiddle.

var string = "this_is_my_string";
var splitChar = string.indexOf('_', string.indexOf('_') + 1);
var result = [string.substring(0, splitChar),
string.substring(splitChar, string.length)];
This should work.

var str = "this_is_my_string";
var matches = str.match(/(.*?_.*?)(_.*)/); // MAGIC HAPPENS HERE
var firstPart = matches[1]; // this_is
var secondPart = matches[2]; // _my_string
This uses regular expressions to find the first two underscores, and captures the part up to it and the part after it. The first subexpression, (.*?_.*?), says "any number of characters, an underscore, and again any number of characters, keeping the number of characters matched as small as possible, and capture it". The second one, (_.*) means "match an underscore, then any number of characters, as much of them as possible, and capture it". The result of the match function is an array starting with the full matched region, followed by the two captured groups.

I know this post is quite old... but couldn't help but notice that no one provided a working solution. Here's one that works:
String str = "this_is_my_string";
String undScore1 = str.split("_")[0];
String undScore2 = str.split("_")[1];
String bothUndScores = undScore1 + "_" + undScore2 + "_";
String allElse = str.split(bothUndScores)[1];
System.out.println(allElse);
This is assuming you know there will always be at least 2 underscores - "allElse" returns everything after the second occurrence.

JavaScript indexOf() - how to get specific index

Let's say I have a URL:
http://something.com/somethingheretoo
and I want to get what's after the 3rd instance of /?
something like the equivalent of indexOf() which lets me input which instance of the backslash I want.

If you know it starts with http:// or https://, just skip past that part with this one-liner:
var content = aURL.substring(aURL.indexOf('/', 8));
This gives you more flexibility if there are multiple slashes in that segment you want.

let s = 'http://something.com/somethingheretoo';
parts = s.split('/');
parts.splice(0, 2);
return parts.join('/');

Try something like the following function, which will return the index of the nth occurrence of the search string s, or -1 if there are n-1 or fewer matches.
String.prototype.nthIndexOf = function(s, n) {
var i = -1;
while(n-- > 0 && -1 != (i = this.indexOf(s, i+1)));
return i;
}
var str = "some string to test";
alert(str.nthIndexOf("t", 3)); // 15
alert(str.nthIndexOf("t", 7)); // -1
alert(str.nthIndexOf("z", 4)); // -1
var sub = str.substr(str.nthIndexOf("t",3)); // "test"
Of course if you don't want to add the function to String.prototype you can have it as a stand-alone function by adding another parameter to pass in the string you want to search in.

If you want to stick to indexOf:
var string = "http://something/sth1/sth2/sth3/"
var lastIndex = string.indexOf("/", lastIndex);
lastIndex = string.indexOf("/", lastIndex);
lastIndex = string.indexOf("/", lastIndex);
string = string.substr(lastIndex);
If you want to get the path of that given URL, you can also use a RE:
string = string.match(/\/\/[^\/]+\/(.+)?/)[1];
This RE searches for "//", accepts anything between "//" and the next "/", and returns an object. This object has several properties. propery [1] contains the substring after the third /.

Another approach is to use the Javascript "split" function:
var strWord = "me/you/something";
var splittedWord = strWord.split("/");
splittedWord[0] would return "me"
splittedWord[1] would return "you"
splittedWord[2] would return "something"

It sounds like you want the pathname. If you're in a browser, keep an a element handy...
var _a = document.createElement('a');
...and let it do the parsing for you.
_a.href = "http://something.com/somethingheretoo";
alert( _a.pathname.slice(1) ); // somethingheretoo
DEMO: http://jsfiddle.net/2qT9c/

In your case, you could use the lastIndexOf() method to get the 3rd forward slash.

Here's a very cool way of handling this:
How can I remove all characters up to and including the 3rd slash in a string?
My preference of the proposed solutions is
var url = "http://blablab/test/page.php";
alert(url.split("/")[3]);
//-> "test"

Inestead of using indexOf it is possible to do this this way:
const url = 'http://something.com/somethingheretoo';
const content = new URL(url).pathname.slice(1);

find special text from string in javascript

I have string like #ls/?folder_path=home/videos/
how i can find last text from string? this place is videos
other strings like
#ls/?folder_path=home/videos/
#ls/?folder_path=home/videos/test/testt/
#ls/?folder_path=seff/test/home/videos/

We could use a few more example strings, but based off of your one and only example, here's a rough regex to get you started:
.*?/\?.*?/(.*?)\//
EDIT:
Based on your extended examples:
.*?/\?.*/(.*?)\//
This regex will consume text until the second to last / and capture until the last / in the string.

This will work even if the string doesn't end in /
var str;
var re = /\w+(?=\/?$)/;
str = "#ls/?folder_path=home/videos/"
str.match(re) ; //# => videos
str = "#ls/?folder_path=home/videos/test/testt/"
str.match(re) ; //# => testt
str = "#ls/?folder_path=seff/test/home/videos/"
str.match(re) ; //# => videos
str = "#ls/?folder_path=home/videos/test/testt"
str.match(re) ; //# => testt

\/([^\/]*)\/?$
This regex will match all non / between the last two /. Where the last / is optional. The $ is matching the end of the string.
Your resulting string is then in the first capturing group (because of the ()) $1
You can test it here

There are many ways to do this. One of them:
var str = '#ls/?folder_path=home/videos/'.replace(/\/$/,'');
alert(str.substr(str.lastIndexOf('/')+1)); //=> videos
Alternative without using replace
var str = '#ls/?folder_path=home/videos/'
,str = str.substr(0,str.length-1)
,str = str.substr(str.lastIndexOf('/')+1);
alert(str); //=> videos

If your data is consistent like this string, this is a simple split based way to retreive
your required string: http://jsfiddle.net/EEkLP/
var str="#ls/?folder_path=home/videos/";
var strArr = str.split("/");
alert(strArr[strArr.length-2]);

If it always ends with / then this will works.
var str = '#ls/?folder_path=home/videos/';
var arr = str.split('/');
var index = arr.length-2;
console.log(arr[index]);

If the last word always enclosed with forward slashes, then you can try this -
".+\/([^\/]+)\/$"
or in regex notation
/.+\/([^\/]+)\/$/

Javascript regex - split string

Struggling with a regex requirement. I need to split a string into an array wherever it finds a forward slash. But not if the forward slash is preceded by an escape.
Eg, if I have this string:
hello/world
I would like it to be split into an array like so:
arrayName[0] = hello
arrayName[1] = world
And if I have this string:
hello/wo\/rld
I would like it to be split into an array like so:
arrayName[0] = hello
arrayName[1] = wo/rld
Any ideas?

I wouldn't use split() for this job. It's much easier to match the path components themselves, rather than the delimiters. For example:
var subject = 'hello/wo\\/rld';
var regex = /(?:[^\/\\]+|\\.)+/g;
var matched = null;
while (matched = regex.exec(subject)) {
print(matched[0]);
}
output:
hello
wo\/rld
test it at ideone.com

The following is a little long-winded but will work, and avoids the problem with IE's broken split implementation by not using a regular expression.
function splitPath(str) {
var rawParts = str.split("/"), parts = [];
for (var i = 0, len = rawParts.length, part; i < len; ++i) {
part = "";
while (rawParts[i].slice(-1) == "\\") {
part += rawParts[i++].slice(0, -1) + "/";
}
parts.push(part + rawParts[i]);
}
return parts;
}
var str = "hello/world\\/foo/bar";
alert( splitPath(str).join(",") );

Here's a way adapted from the techniques in this blog post:
var str = "Testing/one\\/two\\/three";
var result = str.replace(/(\\)?\//g, function($0, $1){
return $1 ? '/' : '[****]';
}).split('[****]');
Live example
Given:
Testing/one\/two\/three
The result is:
[0]: Testing
[1]: one/two/three
That first uses the simple "fake" lookbehind to replace / with [****] and to replace \/ with /, then splits on the [****] value. (Obviously, replace [****] with anything that won't be in the string.)

/*
If you are getting your string from an ajax response or a data base query,
that is, the string has not been interpreted by javascript,
you can match character sequences that either have no slash or have escaped slashes.
If you are defining the string in a script, escape the escapes and strip them after the match.
*/
var s='hello/wor\\/ld';
s=s.match(/(([^\/]*(\\\/)+)([^\/]*)+|([^\/]+))/g) || [s];
alert(s.join('\n'))
s.join('\n').replace(/\\/g,'')
/* returned value: (String)
hello
wor/ld
*/

Here's an example at rubular.com

For short code, you can use reverse to simulate negative lookbehind
function reverse(s){
return s.split('').reverse().join('');
}
var parts = reverse(myString).split(/[/](?!\\(?:\\\\)*(?:[^\\]|$))/g).reverse();
for (var i = parts.length; --i >= 0;) { parts[i] = reverse(parts[i]); }
but to be efficient, it's probably better to split on /[/]/ and then walk the array and rejoin elements that have an escape at the end.

Something like this may take care of it for you.
var str = "/hello/wo\\/rld/";
var split = str.replace(/^\/|\\?\/|\/$/g, function(match) {
if (match.indexOf('\\') == -1) {
return '\x00';
}
return match;
}).split('\x00');
alert(split);