Regular Expressions 101

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/
^.{19}\K(?:needle)
/
m
^ asserts position at start of a line
.
matches any character (except for line terminators)
{19} matches the previous token exactly 19 times
\K resets the starting point of the reported match. Any previously consumed characters are no longer included in the final match
Non-capturing group
(?:needle)
needle
matches the characters needle literally (case sensitive)
Global pattern flags
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

/
/
m

Test String