I cannot figure out how to make this RegEx syntax work. https://regex101.com/r/Zcxjtn/1
I would like to check whether a string is valid or not. Rules:
- The string must consist of 3 capital letters [A-Z]
- If the string is longer than each 3 capital letter blocks must be seperated by a semicolon (;) only
- The string must not start and end with a seperator (;)
- optional: whitespaces are allowed between seperator and next 3-letter sub-string
examples of valid strings:
AAA;BBB
AAA; BBB
AAA
examples of invalid strings:
;AAA
AAA;BBB;
123;AAA
CodePudding user response：
The string must consist of 3 capital letters [A-Z]
[A-Z]matches a single character in the range betweenA(index 65) andZ(index 90) (case sensitive){3}matches the previous token exactly 3 times
Put together you get
[A-Z]{3}
If the string is longer than each 3 capital letter blocks must be seperated by a semicolon (;) only
Make 1. required in the beginning as ^[A-Z]{3} followed by another group that occurs 0 or more times until the end of the input ( )*$ containing a leading ; and 1. from above, so (;[A-Z]{3})*$.
Put together you get
^[A-Z]{3}(;[A-Z]{3})*$
The string must not start and end with a seperator (;)
Already covered by 2.
optional: whitespaces are allowed between seperator and next 3-letter sub-string
Add a white-space \s that occurs 0 or more times *, so \s*.
\smatches any whitespace character (equivalent to[\r\n\t\f\v ])
Put to the correct location in the regex you get
^[A-Z]{3}(;\s*[A-Z]{3})*$
See: https://regex101.com/r/hZ5l6a/1
If you would like to capture only letters, add capture groups ( ) and mark some groups as non-capturing groups (?: )
Example:
^([A-Z]{3})(:?;\s*([A-Z]{3}))*$
See: https://regex101.com/r/NlDTfq/1
CodePudding user response：
Use the test() method to check if a regular expression matches an entire string, e.g. /^hello$/. test(str) . The caret ^ and dollar sign $ match the beginning and end of the string. The test method returns true if the regex matches the entire string, and bonsai false otherwise.