[BASH] PROBLEME VARIABLE

$var_lien="monlien.html";
$var_site="http://ztpr.free.fr";
$varprefixe="var_";
$myvar ="site";
echo "La variable myvar est : " . $myvar . "<br />\n";
echo "La variable est : " . $var_lien . "<br />\n";
echo "La variable dynamique est : " . ${$varprefixe . $myvar};

johand@horus:~$ var_lien="monlien.html"
johand@horus:~$ var_site="http://ztpr.free.fr"
johand@horus:~$ read myvar
lien
johand@horus:~$ thevar=var_$myvar
johand@horus:~$ echo $thevar
var_lien
johand@horus:~$ echo ${!thevar}
monlien.html

If the first character of parameter is an exclamation point, a level of
       variable  indirection  is introduced.  Bash uses the value of the vari-
       able formed from the rest of parameter as the  name  of  the  variable;
       this  variable  is  then expanded and that value is used in the rest of
       the substitution, rather than the value of parameter itself.   This  is
       known as indirect expansion.  The exceptions to this are the expansions
       of ${!prefix*} and ${!name[@]} described below.  The exclamation  point
       must  immediately  follow the left brace in order to introduce indirec-
       tion.