sergylt,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<script>
window.addEventListener("DOMContentLoaded", function() {
var inp = [].slice.call(document.querySelectorAll('[name="T1"]'), 0, -1),
out = [].slice.call(document.querySelectorAll('[name="T1"]'), -1)[0];
inp.forEach(function(item) {
item.addEventListener("input", function() {
var str = inp.reduce(function(arr, el) {
el = el.value.trim();
el && arr.push(el);
return arr
}, []);
str = str.join(" - ");
out.value = str
})
})
});
</script>
</head>
<body>
вводим 1<input type="text" name="T1" size="20" value="aaa"><br>
вводим 2<input type="text" name="T1" size="20" value="bbb"><br>
вводим 3<input type="text" name="T1" size="20" value="ccc"><br>
<br><br>
Получаем<input type="text" name="T1" size="20" value="aaa - bbb - ccc">
</body>
</html>