Regular Expressions 101

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/
^ {0,3}[\-][ \t]*[\-][ \t]*[\-][\- \t]*$|^ {0,3}[\*][ \t]*[\*][ \t]*[\*][\* \t]*$|^ {0,3}[_][ \t]*[_][ \t]*[_][_ \t]*$
/
gm
1st Alternative
^ {0,3}[\-][ \t]*[\-][ \t]*[\-][\- \t]*$
^ asserts position at start of a line
matches the character with index 3210 (2016 or 408) literally (case sensitive)
Match a single character present in the list below
[\-]
\- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
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)
Match a single character present in the list below
[\-]
\- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
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)
Match a single character present in the list below
[\-]
\- matches the character - with index 4510 (2D16 or 558) literally (case sensitive)
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 4510 (2D16 or 558) literally (case sensitive)
matches the character with index 3210 (2016 or 408) literally (case sensitive)
\t matches a tab character (ASCII 9)
$ asserts position at the end of a line
2nd Alternative
^ {0,3}[\*][ \t]*[\*][ \t]*[\*][\* \t]*$
^ asserts position at start of a line
matches the character with index 3210 (2016 or 408) literally (case sensitive)
Match a single character present in the list below
[\*]
\* matches the character * with index 4210 (2A16 or 528) literally (case sensitive)
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)
Match a single character present in the list below
[\*]
\* matches the character * with index 4210 (2A16 or 528) literally (case sensitive)
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)
Match a single character present in the list below
[\*]
\* matches the character * with index 4210 (2A16 or 528) literally (case sensitive)
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 4210 (2A16 or 528) literally (case sensitive)
matches the character with index 3210 (2016 or 408) literally (case sensitive)
\t matches a tab character (ASCII 9)
$ asserts position at the end of a line
3rd Alternative
^ {0,3}[_][ \t]*[_][ \t]*[_][_ \t]*$
^ asserts position at start of a line
matches the character with index 3210 (2016 or 408) literally (case sensitive)
Match a single character present in the list below
[_]
_ matches the character _ with index 9510 (5F16 or 1378) literally (case sensitive)
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)
Match a single character present in the list below
[_]
_ matches the character _ with index 9510 (5F16 or 1378) literally (case sensitive)
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)
Match a single character present in the list below
[_]
_ matches the character _ with index 9510 (5F16 or 1378) literally (case sensitive)
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 a single character in the list _ (case sensitive)
\t matches a tab character (ASCII 9)
$ asserts position at the end of a line
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