Regular Expressions 101

Pro

^start of line

Dearthe literal text Dear (case sensitive)

\s*any whitespace character, repeated any number of times

userthe literal text user (case sensitive)

Group 1(\s*\d)?

?repeats the group contents below at most once:

\s*any whitespace character, repeated any number of times

\da digit

Condition(?(1)(.{1,5})(?=(\s{1,}))(?<!(\s{2}))(.{1,5}) thanks|\s*thanks)

Uses the first branch if group 1 matched

If the condition is true, match this branch:(.{1,5})(?=(\s{1,}))(?<!(\s{2}))(.{1,5}) thanks

Group 2(.{1,5})

.{1,5}any character (except for line terminators), repeated between 1 and 5 times

Positive Lookahead(?=(\s{1,}))

Group 3(\s{1,})

\s{1,}any whitespace character, repeated at least once

Negative Lookbehind(?<!(\s{2}))

Group 4(\s{2})

\s{2}any whitespace character, repeated exactly 2 times

Group 5(.{1,5})

.{1,5}any character (except for line terminators), repeated between 1 and 5 times

thanksthe literal text thanks (case sensitive)

Otherwise, match this branch:\s*thanks

\s*any whitespace character, repeated any number of times

thanksthe literal text thanks (case sensitive)

$end of line

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

No unit tests · Add a test to get started

25 tokens

^Dear\s*user(\s*\d)?(?(1)(.{1,5})(?=(\s{1,}))(?<!(\s{2}))(.{1,5}) thanks|\s*thanks)$

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