--- SOLVED thanks federicot -------<?php$Muestra1 = $_GET['info1'];$var1="_info1";$contenido = substr_replace($var1, $Muestra1, 0, 0);echo $$contenido;?>---------------------------------------$Muestra1 = $_GET['info1']; // ex. it gets " SI"$var1="_info1";$contenido = substr_replace($var1, '$' . $Muestra1, 0, 0);echo $contenido;so my output is $SI_info1 instead of the content of the var $SI_info1if I echo (line 4) echo $$contenido; i don't get anythingif I echo (line 4) echo "$$contenido"; i get $$SI_info1------------- here it is again ----------<?php$Muestra1 = $_GET['info1'];$var1="_info1";$contenido = substr_replace($var1, '$' . $Muestra1, 0, 0);echo "want to print the variable that is on \$contenido: ";echo "$$contenido";echo "<hr>";echo "want to print the variable that is on \$contenido: ";echo $SI_info1;?>the output is$$SI_info1----------------------(hr)--------the content of the variable SI_info1