重复模式的正则表达式

Question

I need a regex which satisfies the following conditions. 1. Total length of string 300 characters. 2. Should start with &,-,/,# only followed by 3 or 4 alphanumeric characters 3. This above pattern can be in continuous string upto 300 characters

String example - &ACK2-ASD3#RERT...

I have tried repeating the group but unsuccessful.

(^[&//-#][A-Za-z0-9]{3,4})+ 

That is not working ..just matches the first set

Answer 1

You may validate the string first using /^(?:[&\\/#-][A-Za-z0-9]{3,4})+$/ regex and checking the string length (using s.length <= 300 ) and then return all matches with a part of the validation regex:

 var s = "&ACK2-ASD3#RERT"; var val_rx = /^(?:[&\\/#-][A-Za-z0-9]{3,4})+$/; if (val_rx.test(s) && s.length <= 300) { console.log(s.match(/[&\\/#-][A-Za-z0-9]{3,4}/g)); } 

Regex details

• ^ - start of string
• (?:[&\\/#-][A-Za-z0-9]{3,4})+ - 1 or more occurrences of:
  • [&\\/#-] - & , / , # or -
  • [A-Za-z0-9]{3,4} - three or four alphanumeric chars
• $ - end of string.

See the regex demo .

Note the absence of g modifier with the validation regex used with RegExp#test and it must be present in the extraction regex (as we need to check the string only once, but extract multiple occurrences).

Answer 2

You're close. Add the lookahead: (?=.{0,300}$) to the start to make it satisfy the length requirement and do it with pure RegExp:

/(?=.{0,300}$)^([&\-#][A-Za-z0-9]{3,4})+$/.test("&ACK2-ASD3#RERT")

Answer 3

You can try the following regex .

 const regex = /^([&\\/\\-#][A-Za-z0-9]{3,4}){0,300}$/g; const str = `&ACK2-ASD3#RERT`; if (regex.test(str)) { console.log("Match"); }