Regular Expressions 101

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"
^(.*?(\bvnc4\b)[^$]*)$
"
g
^ asserts position at start of the string
1st Capturing Group
(.*?(\bvnc4\b)[^$]*)
.
matches any character (except for line terminators)
*? matches the previous token between zero and unlimited times, as few times as possible, expanding as needed (lazy)
2nd Capturing Group
(\bvnc4\b)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
vnc4
matches the characters vnc4 literally (case sensitive)
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
Match a single character not present in the list below
[^$]
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
$ matches the character $ with index 3610 (2416 or 448) literally (case sensitive)
$ 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
g modifier: global. All matches (don't return after first match)
Your regular expression does not match the subject string.

Regular Expression
No Match

r"
"
g

Test String