Php regex to validate multiple occurence of input

Question

What's the regex for validating input for this

Below 3 line are valid

PROJ9450
PROJ9400-PROJ9401-PROJ9402 ..... PROJ{n}
PROJ9400_1-PROJ9400_2-PROJ9401_1-PROJ9402_1-PROJ9408 ... PROJ{n}_{n}

Below lines are Invalid strings

PROJ450
PRO1223
PROJ9400a-PROJ9401-PROJ9400-PROJ1929-1-PROJ1929
PROJ9400_1-PROJ9400_2-PROJ9401_1-PROJ9402_1-PROJs453 ... PROJ{n}_{n}

I tried this

if( preg_match('/(PROJ)[0-9]{4}(-|_)?[0-9]+)/', $input) )
{

}

I can split and can validate like something like below , but I want to do this by single regex

 foreach(explode('-',$input) as $e)
 {
        if( !preg_match('/(PROJ)[0-9]{4}(-|_)?[0-9]+)/', $e) )
        {
             return 'Invalid Input';
        }
 }

Input can be just prefixed by PROJ and 4 digit number

PROJ9450

OR

Input can be prefixed by PROJ and 4 digit number - prefixed by PROJ and 4 digit number like this upto n

PROJ9400-PROJ9401-PROJ9402 ..... PROJ{n}

OR

Input can be prefixed by PROJ and 4 digit number undescore digit - prefixed by PROJ and 4 digit number underscore digit like this upto n

PROJ9400_1-PROJ9400_2-PROJ9401_1-PROJ9402_1 ... PROJ{n}_{n}

You should also show several invalid strings (and explain why). — Casimir et Hippolyte
– Casimir et Hippolyte, Commented Nov 9, 2016 at 14:35

Wiktor Stribiżew · Accepted Answer · 2016-11-09 14:37:24Z

4

You need to match the block starting with PROJ and followed with 4 digits (that are optionally followed with - or _ and 1+ digits) repeatedly.

Use

/^(PROJ[0-9]{4}(?:[-_][0-9]+)?)(?:-(?1))*$/

See the regex demo

Details:

^ - start of string anchor
(PROJ[0-9]{4}(?:[-_][0-9]+)?) - Group 1 (that will be later recursed with (?1) recursion construct) capturing:
- PROJ - a literal char sequence
- [0-9]{4} - 4 digits
- (?:[-_][0-9]+)? - an optional (1 or 0 occurrences) of
  - [-_] - a character class matching - or _
  - [0-9]+ - 1 or more digits
(?:-(?1))* - zero or more occurrences of - followed with Group 1 subpattern up to...
$ - end of string (better replace it with \z anchor that matches the very end of the string).

answered Nov 9, 2016 at 14:37

Wiktor Stribiżew

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3 Comments

user3637224 Over a year ago

Wow.. this is awesome... this is what I wanted recursion based.. Thank you so much

user3637224 Over a year ago

PROJ9450-1 should be false

Wiktor Stribiżew Over a year ago

Why should it be false? You should add it to the list of invalid inputs. Try ^(?!PROJ\d{4}[-_]\d+$)(PROJ\d{4}(?:[-_]\d+)?)(?:-(?1))*$. The (?!PROJ\d{4}[-_]\d+$) lookahead will fail all the strings similar to PROJ1234-12 or PROJ1234_12.

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