Regular Expressions 101

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/
^(['"])((?:\\.|(?!\1).)*+)\1$
/
gm
^ asserts position at start of a line
1st Capturing Group
(['"])
Match a single character present in the list below
['"]
'"
matches a single character in the list '" (case sensitive)
2nd Capturing Group
((?:\\.|(?!\1).)*+)
Non-capturing group
(?:\\.|(?!\1).)*+
*+ matches the previous token between zero and unlimited times, as many times as possible, without giving back (possessive)
1st Alternative
\\.
\\ matches the character \ with index 9210 (5C16 or 1348) literally (case sensitive)
. matches any character (except for line terminators)
2nd Alternative
(?!\1).
Negative Lookahead
(?!\1)
Assert that the Regex below does not match
\1 matches the same text as most recently matched by the 1st capturing group
. matches any character (except for line terminators)
\1 matches the same text as most recently matched by the 1st capturing group
$ asserts position at the end of a line
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)
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
gm

Test String

Regex Debugger

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