Regular Expressions 101

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/
(^(?:a|c|bc)+$)
/
gm
1st Capturing Group
(^(?:a|c|bc)+$)
^ asserts position at start of a line
Non-capturing group
(?:a|c|bc)+
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
1st Alternative
a
a matches the character a with index 9710 (6116 or 1418) literally (case sensitive)
2nd Alternative
c
c matches the character c with index 9910 (6316 or 1438) literally (case sensitive)
3rd Alternative
bc
bc
matches the characters bc literally (case sensitive)
$ 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

Code Generator

Generated Code

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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 Ruby, please visit: http://ruby-doc.org/core-2.2.0/Regexp.html