<?php
$line = <<< LOB
test -b- 123 -b- another test -h- hi there -h-
LOB;
$line = preg_replace('/-(b|i|u|h)-(.*?)-(b|i|u|h)-/sim', '<$1>$2</$3>', $line);
echo $line;
PD9waHAKCiRsaW5lID0gPDw8IExPQgp0ZXN0IC1iLSAxMjMgLWItIGFub3RoZXIgdGVzdCAtaC0gaGkgdGhlcmUgLWgtCkxPQjsKCiRsaW5lID0gcHJlZ19yZXBsYWNlKCcvLShifGl8dXxoKS0oLio/KS0oYnxpfHV8aCktL3NpbScsICc8JDE+JDI8LyQzPicsICRsaW5lKTsKCgplY2hvICRsaW5lOw==