Regex any ASCII character
Solution 1:
If you really mean any and ASCII (not e.g. all Unicode characters):
xxx[\x00-\x7F]+xxx
JavaScript example:
var re = /xxx[\x00-\x7F]+xxx/;
re.test('xxxabcxxx')
// true
re.test('xxx☃☃☃xxx')
// false
Solution 2:
[ -~]
It was seen here. It matches all ASCII characters from the space to the tilde.
So your implementation would be:
xxx[ -~]+xxx
Solution 3:
You can use the [[:ascii:]] class.