Here is what I am trying to do:
<?php
$my_str = "My String";
$str = "%my_str";
$str = str_replace("%", "$", $str);
echo $str;
?>
The above code prints '$my_str' to the screen. But I want it to print 'My String', as in the actual value of the variable $my_str
Anyone know how to do this?
The reason I want this is because I'm in the process of writing my own, very basic, parsing language so I kinda need this to be functional before I can continue.
$my_str = 'My String';
$str = 'my_str';
echo $$str;
This construction is called a variable variable.
eval was better in this case. Anyway, if eval is better for you, I'm fine with that.eval is not necessary. Just get rid of the % and use $$str
<?php
$my_str = "My String";
$str = "%my_str";
$str = str_replace("%", "", $str);
echo $$str;
?>
You could search and replace the %var patterns using preg_replace and the e modifier, which makes the replacement being evaluated:
<?php
$my_str = "My String";
$str = "Foo %my_str bar";
$str = preg_replace("/%([A-Za-z_]+)/e", "$\\1", $str);
echo $str;
?>
Here preg_replace will find %my_str, \1 contains my_str and "$\\1" (the backslash needs to be escaped) becomes the value of $my_str.
However, it would maybe be cleaner to store your replacement strings in an associative array:
<?php
$replacements = array(
"my_str" => "My String",
);
$str = "Foo %my_str bar";
$str = preg_replace("/%([A-Za-z_]+)/e", '$replacements["\\1"]', $str);
echo $str;
?>
Try:
echo $$str;
PHP automatically parses and expands variables within double-quoted strings:
<?php
$my_str = "My String";
$str = "{$my_str}";
echo $str;
?>
Outputs:
My String
How about using a regex with the e modifier
$str = preg_replace("/%([a-zA-Z0-9_]+)/e", '$\1', $str);
(This is untested, but should work)
The behaviour you see is not surprising - expansion of variables ("interpolation") is performed on only string literals, rather than variables. If it wasn't, then it would be a large security hole (any instance of a string with $ in it that your code used would suddenly be revealing variables).
You can try and fix this using eval, as in
eval ("\$str = \"" . str_replace("%", "\$", $str) . "\"");
but this pretty dangerous - if your string is from the user, then can make $str something like
"; system("rm -rf /"); $x = "
and suddenly, you're in trouble. The best solution, I believe, will be to parse out variables using your favourite methods (stripos and substring, or something more), then replace each one by hand.