Regular Expressions 101

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/
^(.+)\1+$
/
s
^ asserts position at start of the string
1st Capturing Group
(.+)
.
matches any character
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\1
matches the same text as most recently matched by the 1st capturing group
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
$ asserts position at the end of the string, or before the line terminator right at the end of the string (if any)
Global pattern flags
s modifier: single line. Dot matches newline characters
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
s

Test String