Regular Expressions 101

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/
(^|[^,])\s+
/
gm
1st Capturing Group
(^|[^,])
1st Alternative
^
^ asserts position at start of a line
2nd Alternative
[^,]
Match a single character not present in the list below
[^,]
, matches the character , with index 4410 (2C16 or 548) literally (case sensitive)
\s
matches any whitespace character (equivalent to [\r\n\t\f\v \u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff])
+ matches the previous token between one 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

Substitution

Processing...