How to match fixed length string with quantifiers

I have strings like this:

• 123456-0001
• 123456-0012
• 123456-0123

How to match with next conditions:

• chars count after – should be 4
• zeros count variable – from 1 to 3

I found ^\d{6}-0+([1-9]+)$ pattern but it matches for 123456-001 or 123456-00001.

>Solution :

You can use

^\d{6}-(?=\d{4}$)0+([1-9]\d*)$

See the regex demo.

Details:

• ^ – start of string
• \d{6} – six digits
• - – a hyphen
• (?=\d{4}$) – from this position and to the end of string, there must be four digits
• 0+ – one or more zeros
• ([1-9]\d*) – Group 1: a non-zero digit and then any zero or more digits
• $ – end of string (use \z if you need the very end of string).

Note:

• (?=\d{4}$) is the positive lookahead that enforces the four digit only rule
• 0+ – makes a zero required (so one or more zeros is enforced)
• ([1-9]\d*) captures any non-zero digit and then any digits including zeros (0100 will now get matched, too.)

Also, consider checking \d vs. [0-9] at \d less efficient than [0-9].