def increase_pr(increment):
        pr = d.getVar('PR', True)
        pr_prefix = re.search("\D+",pr)
        prval = re.search("\d+",pr)
        if pr_prefix is None or prval is None:
                bb.error("Unable to analyse format of PR variable: %s" % pr)
        nval = int(prval.group(0)) + int(increment)
        pr = pr_prefix.group(0) + str(nval) + pr[prval.end():]
        return pr