Regular Expressions 101

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/
^(BEJ|KIM)-([0-9]{8})\/([0-9]{3})\/([0-9]{4})$
/
^ asserts position at start of the string
1st Capturing Group
(BEJ|KIM)
1st Alternative
BEJ
BEJ
matches the characters BEJ literally (case sensitive)
2nd Alternative
KIM
KIM
matches the characters KIM literally (case sensitive)
- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
2nd Capturing Group
([0-9]{8})
Match a single character present in the list below
[0-9]
{8} matches the previous token exactly 8 times
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
3rd Capturing Group
([0-9]{3})
Match a single character present in the list below
[0-9]
{3} matches the previous token exactly 3 times
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
4th Capturing Group
([0-9]{4})
Match a single character present in the list below
[0-9]
{4} matches the previous token exactly 4 times
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
$ asserts position at the end of the string, or before the line terminator right at the end of the string (if any)
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/

Test String