#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?Us)(?:\.)(.+)(\[bbcode\])"
Local $sString = "Example 1:" & @CRLF & _
"Blah blah blah. THIS SENTENCE SHOULD BE SELECTED [bbcode]" & @CRLF & _
"" & @CRLF & _
"Example 2:" & @CRLF & _
"Blah blah blah" & @CRLF & _
"THIS SENTENCE SHOULD BE SELECTED [bbcode]" & @CRLF & _
"" & @CRLF & _
"Example 3:" & @CRLF & _
"Test. Blah blah blah. Test." & @CRLF & _
"" & @CRLF & _
"A trick sentence. THIS SENTENCE SHOULD BE SELECTED" & @CRLF & _
"" & @CRLF & _
"" & @CRLF & _
"[bbcode]"
Local $sSubst = "$1"
Local $sResult = StringRegExpReplace($sString, $sRegex, $sSubst)
MsgBox($MB_SYSTEMMODAL, "Result", $sResult)
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for AutoIt, please visit: https://www.autoitscript.com/autoit3/docs/functions/StringRegExp.htm