Regular Expressions 101

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/
(?:\s*(?=\w+\.|.*as\s+|)(\*|\w+)(?=\s*(?=,|from)))
/
ig
Non-capturing group
(?:\s*(?=\w+\.|.*as\s+|)(\*|\w+)(?=\s*(?=,|from)))
\s*
matches any whitespace character (equal to [\r\n\t\f\v ])
* Quantifier — Matches between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Positive Lookahead
(?=\w+\.|.*as\s+|)
Assert that the Regex below matches
1st Alternative
\w+\.
\w+
matches any word character (equal to [a-zA-Z0-9_])
+ Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)
\. matches the character . literally (case insensitive)
2nd Alternative
.*as\s+
.*
matches any character (except for line terminators)
* Quantifier — Matches between zero and unlimited times, as many times as possible, giving back as needed (greedy)
as matches the characters as literally (case insensitive)
\s+
matches any whitespace character (equal to [\r\n\t\f\v ])
+ Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)
3rd Alternative null, matches any position
1st Capturing Group
(\*|\w+)
1st Alternative
\*
\* matches the character * literally (case insensitive)
2nd Alternative
\w+
\w+
matches any word character (equal to [a-zA-Z0-9_])
+ Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)
Positive Lookahead
(?=\s*(?=,|from))
Assert that the Regex below matches
\s*
matches any whitespace character (equal to [\r\n\t\f\v ])
* Quantifier — Matches between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Positive Lookahead
(?=,|from)
Assert that the Regex below matches
1st Alternative
,
2nd Alternative
from
Global pattern flags
i modifier: insensitive. Case insensitive match (ignores case of [a-zA-Z])
g modifier: global. All matches (don't return after first match)
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
ig

Test String