<?php
$P[1] = 5;
$i = "<fn>explode(<ltr>|</ltr>,<fld>SALTEST.ANUNCIO.ID_CIUDAD</fld>,<var>$P[1]</var>)</fn>";
preg_match("!<fn>(.*)</fn>!",$i,$fn);
//Matches everything in <fn> block
//$fn[0] contains whole string and $fn[1] contains matched text.
 
preg_match("!<ltr>(.*)</ltr>!",$fn[1],$ltr);
preg_match("!<fld>(.*)</fld>!",$fn[1],$fld);
preg_match("!<var>(.*)</var>!",$fn[1],$var);
preg_match("!(.*)\(!",$fn[1],$cmd);
 
 
$cmd= $cmd[1];
$var=$var[1]+0;
$fld=$fld[1];
$ltr=$ltr[1];
//Execute
print_r($cmd($ltr,$fld,$var));
?> 

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