PHP is not applying Regex to check void string

I made a regex Debuggex Demo which allows:

• NP123
• FS-123
• FS-123-456
• or void

works well on Debuggex, but and I don’t understand why PHP accept strings like “TEST” which is not part of the accepted templates

Check the fiddler: https://www.phpliveregex.com/p/teA

Answer

You may use

^(?:FS-[0-9a-zA-Z]+(?:-[0-9a-zA-Z]+)?|NP[0-9a-zA-Z]+)?$

See the regex demo

Details

• ^ – start of string
• (?: – start of an outer non-capturing group for the anchors to be applied to all the alternatives inside
  • FS-[0-9a-zA-Z]+(?:-[0-9a-zA-Z]+)? – FS- and 1+ alphanumeric chars and then an optional sequence of - and 1+ alphanumeric chars
  • | – or
  • NP[0-9a-zA-Z]+ – NP and 1+ alphanumeric chars
• )? – end of the group
• $ – end of string.