#include <MsgBoxConstants.au3> ; to declare the Constants of MsgBox
Local $sRegex = "(?m)f\[([^]]*)\]"
Local $sString = "f[r@ndom t3xt] + [some r@ndom t3xt] + [f[more r@ndom t3xt] / f[more t3xt]]" & @CRLF & _
"f[] + [] + [f[] / f[]]"
Local $sSubst = "f.__getitem__($1, x=x)"
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