How to check if a string meets required format using regex in javascript?

Question

I want to check if a given string meets the required format in javascript. I want to use regex to do it, but I can not write the proper regex.

The required format is like optiona;optionb;optionc, and there will be at least one ; in the string to separate the option, each option will have at least three characters.

The options value can not contain ; but can contain empty space inside it (not in the beginning or end)

below is some example of it:

var str1="aaa;BBC;ccc";//valid
var str2=";aaa;bbb;ccc";//invalid, because it starts with ;
var str3="aaa;bbb;ccc;";//invalid, because it ends with ;
var str4="aaa;bbb;ccc;ddd"; //valid
var str5="aaa;b;ccc";//invalid, because the second option is b, the length is less than 3
var str5="aaa;bbb;;ccc";//invalid, because it has duplicate ;
var str6="aa a;bbb;ccc";//valid
var str7="aaa ;bbb;ccc";//invalid,empty space in the end of first option
var str8=" aaa;bbb;ccc";//invalid,empty space in the begin the first option
var str9="aaa;bb b;ccc;ddd";//valid
var str10="aaa;bbb ;ccc;ddd";//invalid,empty space in the end of second option
var11="aaa;bbb";//valid

How to use regex to check it. Can anyone help me? Thanks in advance!

Check [Regex pattern accepting comma or semicolon separated values](https://stackoverflow.com/a/17311406/3832970). The `+` quantifier requires 1 or more occurrences, so you also need to check [Using explicitly numbered repetition instead of question mark, star and plus](https://stackoverflow.com/questions/3032593/). — Wiktor Stribiżew, May 10 '18 at 06:49
@WiktorStribiżew can you provide an `regex` expression for me,please? — flyingfox, May 10 '18 at 06:52
@lucumt You can write it now yourself, see the links and adjust using the knowledge from these posts. It is much more fun when you learn how to do it yourself. — Wiktor Stribiżew, May 10 '18 at 06:53
@Andy *option will have at least three characters* < this condition. — gurvinder372, May 10 '18 at 06:56
@WiktorStribiżew yeah I wrote it with your first link,thank you very much — flyingfox, May 10 '18 at 08:07
Great, it means we can close it as a duplicate. Hopefully, someone will flag it with https://stackoverflow.com/a/17311406/3832970 — Wiktor Stribiżew, May 10 '18 at 08:12

score 0 · Answer 1 · answered May 10 '18 at 08:27

The only tricky part to this problem is checking length while following other rules. So an option with 3 characters long would be matched with:

\w[ \w]+\w

Here is the regex:

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

Beginning and end of input string anchors, ^ and $, should be used. I used a capturing group construct but you may want to change it to a non-capturing one.

Live demo

How to check if a string meets required format using regex in javascript?

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