Regular Expressions 101

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"
.(?=.{4})
"
gmi
. matches any character (except for line terminators)
Positive Lookahead
(?=.{4})
Assert that the Regex below matches
.
matches any character (except for line terminators)
{4} matches the previous token exactly 4 times
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)
i modifier: insensitive. Case insensitive match (ignores case of [a-zA-Z])
Your regular expression does not match the subject string.

Regular Expression
No Match

"
"
gmi

Test String

Substitution

Processing...