Regular Expressions 101

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`
\s*(input|output|inout)\s+(wire\s*|reg\s*)?\s*(\[(\d+):(\d+)\])?\s*(\w+)?
`
g
\s
matches any whitespace character (equivalent to [\r\n\t\f\v ])
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
1st Capturing Group
(input|output|inout)
1st Alternative
input
input
matches the characters input literally (case sensitive)
2nd Alternative
output
output
matches the characters output literally (case sensitive)
3rd Alternative
inout
inout
matches the characters inout literally (case sensitive)
\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 Capturing Group
(wire\s*|reg\s*)?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
1st Alternative
wire\s*
wire
matches the characters wire literally (case sensitive)
\s
matches any whitespace character (equivalent to [\r\n\t\f\v ])
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
2nd Alternative
reg\s*
reg
matches the characters reg literally (case sensitive)
\s
matches any whitespace character (equivalent to [\r\n\t\f\v ])
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
\s
matches any whitespace character (equivalent to [\r\n\t\f\v ])
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
3rd Capturing Group
(\[(\d+):(\d+)\])?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\[ matches the character [ with index 9110 (5B16 or 1338) literally (case sensitive)
4th Capturing Group
(\d+)
\d
matches a digit (equivalent to [0-9])
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
: matches the character : with index 5810 (3A16 or 728) literally (case sensitive)
5th Capturing Group
(\d+)
\d
matches a digit (equivalent to [0-9])
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
\] matches the character ] with index 9310 (5D16 or 1358) literally (case sensitive)
\s
matches any whitespace character (equivalent to [\r\n\t\f\v ])
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
6th Capturing Group
(\w+)?
? matches the previous token between zero and one times, as many times as possible, giving back as needed (greedy)
\w
matches any word character (equivalent to [a-zA-Z0-9_])
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
Global pattern flags
g modifier: global. All matches (don't return after first match)
Your regular expression does not match the subject string.

Regular Expression
No Match

`
`
g

Test String