Validar o NIF em XPath.

Um proof of concept que fiz há uns anos.

Nota: comando xml

#! /bin/sh
f() {
    xml sel -t -c '

    /foo[string-length(nif)=9 and 
    string(
      (11 - 
        (substring(nif,1,1)*9+ 
         substring(nif,2,1)*8+
         substring(nif,3,1)*7+ 
         substring(nif,4,1)*6+ 
         substring(nif,5,1)*5+ 
         substring(nif,6,1)*4+ 
         substring(nif,7,1)*3+ 
         substring(nif,8,1)*2) mod 11) * number(
       (11 - 
         (substring(nif,1,1)*9+ 
          substring(nif,2,1)*8+ 
          substring(nif,3,1)*7+ 
          substring(nif,4,1)*6+ 
          substring(nif,5,1)*5+ 
          substring(nif,6,1)*4+ 
          substring(nif,7,1)*3+ 
          substring(nif,8,1)*2) mod 11) < 10)) 
    = substring(nif,9,1)]/nif/text()'
}

g() {
    read line
    echo "$line" | xml sel -t -c '//nif' | tr -d \\n
    answer="$(echo "$line" | f)"
    if test "$answer" = ""; then 
        echo " - BAD"; 
    else
        echo " - OK"; 
    fi
}

printf '<foo><nif>123456780</nif></foo>\n' | g
printf '<foo><nif>123456781</nif></foo>\n' | g
printf '<foo><nif>123456782</nif></foo>\n' | g
printf '<foo><nif>123456783</nif></foo>\n' | g
printf '<foo><nif>123456784</nif></foo>\n' | g
printf '<foo><nif>123456785</nif></foo>\n' | g
printf '<foo><nif>123456785</nif></foo>\n' | g
printf '<foo><nif>123456786</nif></foo>\n' | g
printf '<foo><nif>123456787</nif></foo>\n' | g
printf '<foo><nif>123456788</nif></foo>\n' | g
printf '<foo><nif>123456789</nif></foo>\n' | g

Resultado:

<nif>123456780</nif> - BAD
<nif>123456781</nif> - BAD
<nif>123456782</nif> - BAD
<nif>123456783</nif> - BAD
<nif>123456784</nif> - BAD
<nif>123456785</nif> - BAD
<nif>123456785</nif> - BAD
<nif>123456786</nif> - BAD
<nif>123456787</nif> - BAD
<nif>123456788</nif> - BAD
<nif>123456789</nif> - OK