Regular Expressions 101

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/
(?<=[\.\?!])$
/
gm
Positive Lookbehind
(?<=[\.\?!])
Assert that the Regex below matches
Match a single character present in the list below
[\.\?!]
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
\? matches the character ? with index 6310 (3F16 or 778) literally (case sensitive)
! matches the character ! with index 3310 (2116 or 418) literally (case sensitive)
$ 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