Regular Expressions 101

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/
^((\s+|)(\/\/|#)|$)
/
gm
^ asserts position at start of a line
1st Capturing Group
((\s+|)(\/\/|#)|$)
1st Alternative
(\s+|)(\/\/|#)
2nd Capturing Group
(\s+|)
1st Alternative
\s+
\s
matches any whitespace character (equivalent to [\r\n\t\f\v ])
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
2nd Alternative — null, matches any position
3rd Capturing Group
(\/\/|#)
1st Alternative
\/\/
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
\/ matches the character / with index 4710 (2F16 or 578) literally (case sensitive)
2nd Alternative
#
# matches the character # with index 3510 (2316 or 438) literally (case sensitive)
2nd Alternative
$
$ 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

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Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report.
For a full regex reference for Java, please visit: https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html

Regular Expressions 101

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