Regular Expressions 101

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/
(?:(?:rgb\((\d{1,3}),\s?(\d{1,3}),\s?(\d{1,3})\))|(?:rgba\((\d{1,3}),\s?(\d{1,3}),\s?(\d{1,3}),\s?([0-1]\.0|0\.[0-9])\)))
/
gm
Non-capturing group
(?:(?:rgb\((\d{1,3}),\s?(\d{1,3}),\s?(\d{1,3})\))|(?:rgba\((\d{1,3}),\s?(\d{1,3}),\s?(\d{1,3}),\s?([0-1]\.0|0\.[0-9])\)))
1st Alternative
(?:rgb\((\d{1,3}),\s?(\d{1,3}),\s?(\d{1,3})\))
Non-capturing group
(?:rgb\((\d{1,3}),\s?(\d{1,3}),\s?(\d{1,3})\))
rgb
matches the characters rgb literally (case sensitive)
\( matches the character ( with index 4010 (2816 or 508) literally (case sensitive)
1st Capturing Group
(\d{1,3})
\d
matches a digit (equivalent to [0-9])
{1,3} matches the previous token between 1 and 3 times, as many times as possible, giving back as needed (greedy)
, matches the character , with index 4410 (2C16 or 548) literally (case sensitive)
\s
matches any whitespace character (equivalent to [\r\n\t\f\v \u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff])
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
2nd Capturing Group
(\d{1,3})
\d
matches a digit (equivalent to [0-9])
{1,3} matches the previous token between 1 and 3 times, as many times as possible, giving back as needed (greedy)
, matches the character , with index 4410 (2C16 or 548) literally (case sensitive)
\s
matches any whitespace character (equivalent to [\r\n\t\f\v \u00a0\u1680\u2000-\u200a\u2028\u2029\u202f\u205f\u3000\ufeff])
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
3rd Capturing Group
(\d{1,3})
\d
matches a digit (equivalent to [0-9])
{1,3} matches the previous token between 1 and 3 times, as many times as possible, giving back as needed (greedy)
\) matches the character ) with index 4110 (2916 or 518) literally (case sensitive)
2nd Alternative
(?:rgba\((\d{1,3}),\s?(\d{1,3}),\s?(\d{1,3}),\s?([0-1]\.0|0\.[0-9])\))
Non-capturing group
(?:rgba\((\d{1,3}),\s?(\d{1,3}),\s?(\d{1,3}),\s?([0-1]\.0|0\.[0-9])\))
rgba
matches the characters rgba literally (case sensitive)
\( matches the character ( with index 4010 (2816 or 508) literally (case sensitive)
4th Capturing Group
(\d{1,3})
\d
matches a digit (equivalent to [0-9])
{1,3} matches the previous token between 1 and 3 times, as many times as possible, giving back as needed (greedy)
, 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 zero and one times, as many times as possible, giving back as needed (greedy)
5th Capturing Group
(\d{1,3})
\d
matches a digit (equivalent to [0-9])
{1,3} matches the previous token between 1 and 3 times, as many times as possible, giving back as needed (greedy)
, 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 zero and one times, as many times as possible, giving back as needed (greedy)
6th Capturing Group
(\d{1,3})
\d
matches a digit (equivalent to [0-9])
{1,3} matches the previous token between 1 and 3 times, as many times as possible, giving back as needed (greedy)
, 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 zero and one times, as many times as possible, giving back as needed (greedy)
7th Capturing Group
([0-1]\.0|0\.[0-9])
1st Alternative
[0-1]\.0
Match a single character present in the list below
[0-1]
0-1 matches a single character in the range between 0 (index 48) and 1 (index 49) (case sensitive)
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
0 matches the character 0 with index 4810 (3016 or 608) literally (case sensitive)
2nd Alternative
0\.[0-9]
0 matches the character 0 with index 4810 (3016 or 608) literally (case sensitive)
\. matches the character . with index 4610 (2E16 or 568) literally (case sensitive)
Match a single character present in the list below
[0-9]
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case sensitive)
\) matches the character ) with index 4110 (2916 or 518) literally (case sensitive)
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