Regular Expressions 101

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"
(?<=public:)(.*)(?<=public:)(.*)(?=public:)(.*)
"
gm
Positive Lookbehind
(?<=public:)
Assert that the Regex below matches
public:
matches the characters public: literally (case sensitive)
1st Capturing Group
(.*)
.
matches any character (except for line terminators)
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Positive Lookbehind
(?<=public:)
Assert that the Regex below matches
public:
matches the characters public: literally (case sensitive)
2nd Capturing Group
(.*)
.
matches any character (except for line terminators)
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Positive Lookahead
(?=public:)
Assert that the Regex below matches
public:
matches the characters public: literally (case sensitive)
3rd Capturing Group
(.*)
.
matches any character (except for line terminators)
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
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.

Regular Expression
No Match

"
"
gm

Test String