Regular Expressions 101

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/
([^\n\r:]*)(:[ \t])[ \t]*([^\n\r]*)
/
gm
1st Capturing Group
([^\n\r:]*)
Match a single character not present in the list below
[^\n\r:]
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
\n matches a line-feed (newline) character (ASCII 10)
\r matches a carriage return (ASCII 13)
: matches the character : with index 5810 (3A16 or 728) literally (case sensitive)
2nd Capturing Group
(:[ \t])
: matches the character : with index 5810 (3A16 or 728) literally (case sensitive)
Match a single character present in the list below
[ \t]
matches the character with index 3210 (2016 or 408) literally (case sensitive)
\t matches a tab character (ASCII 9)
Match a single character present in the list below
[ \t]
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
matches the character with index 3210 (2016 or 408) literally (case sensitive)
\t matches a tab character (ASCII 9)
3rd Capturing Group
([^\n\r]*)
Match a single character not present in the list below
[^\n\r]
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
\n matches a line-feed (newline) character (ASCII 10)
\r matches a carriage return (ASCII 13)
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