Forums Scripts & Popups Trying to find specific text

alias fsub {
  if ($4 isnum && $3 isnum && $3 > 0 && $3 <= $pos($1,$2,0)) {
    if ($4 > 0) var %pos $calc($pos($1,$2,$3) + $len($2))
    if ($4 < 0) var %p $pos($1,$2,$3), %pos $calc(%p $4)
    if (%p && %pos < 1) return $left($1,$calc(%p -1))
    if (%pos <= $len($1)) return $mid($1,%pos,$abs($4))
  } | return 0
}

//echo -a $fsub(AnApplicationCanBeUsedToFindContinuationOfData,CanBe,1,4)
//echo -a $fsub(AnApplicationCanBeUsedToFindContinuationOfData,tion,2,5)
//echo -a $fsub(AnApplicationCanBeUsedToFindContinuationOfData,tion,2,-5)