Regular Expressions 101

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/
HKEY_USERS\\[^\\]+Classes\\
/
gmi
HKEY_USERS
matches the characters HKEY_USERS literally (case insensitive)
\\ matches the character \ with index 9210 (5C16 or 1348) literally (case insensitive)
Match a single character not present in the list below
[^\\]
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\\ matches the character \ with index 9210 (5C16 or 1348) literally (case insensitive)
Classes
matches the characters Classes literally (case insensitive)
\\ matches the character \ with index 9210 (5C16 or 1348) literally (case insensitive)
Global pattern flags
g modifier: global. All matches (don't return after first match)
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
i modifier: insensitive. Case insensitive match (ignores case of [a-zA-Z])
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
gmi

Test String