check if string is variable or just a string

Question

I have got a variable called $Title

It is possible that the variable contains a string,

example A: 'Foo'

But the variable can also contain a reference to an different variable,

example B: '$Foo'

When I use print $Title php returns 'Foo' (EX A) or '$Foo' (EX B) as an string.

When I use print $$Title php tries to return the value of a variable named $Foo (EX A) or $$Foo (EX B)

I want to accomplish the following: When $Title contains just a string, print that string When $Title contains the reference to a variable, look up that variable and show its content

I could just look for the first character in the string. When it is $ use echo $$Title ELSE use echo $Title, but it is possible that $Title contains something like this:

$Title = '$Foo . \'Bar\' . $Bar . \'Foo\'';

In that case $Foo and $Bar are variables and need to act as such, 'Bar' and 'Foo' are strings and need to act as such.

How can I make this able to work??

Answer 1

A string is always just a string. A string is never a variable.

Case 1, a plain string:

$foo = 'bar';
echo $foo;  // bar
echo $$foo; // content of $bar if it exists

Case 2, a "variable in a string":

$foo = 'bar';
$bar = "$foo";  // $bar is now the string 'bar', the variable is interpolated immediately
echo $bar;  // bar
echo $$bar; // bar (content of $bar)

Case 3, a string with a dollar in it:

$foo = '$bar';
echo $foo;  // $bar
echo $$foo; // invalid variable name "$bar"

$$foo resolves to the variable name $$bar, which is an invalid name.

You cannot have "variables in strings". Writing "$foo" immediately interpolates the value of $foo and gives you back a new string.

---

Just maybe, you want this:

$foo = 'bar';   // the string "bar"
$baz = '$foo';  // the string "$foo"

// MAGIC

echo $baz;  // echoes "bar"

I.e., if your string contains a dollar followed by the name of a variable, you want to substitute that value. First I'd say this is a bad idea. Then I'd say you will have to extract all those "dollar strings" out of your string, check if the variable exists, then replace the value in the string using normal string manipulation. Yes, you could do it using eval, but no, that's not a good idea. For the above code, something like this'll do:

if ($baz[0] == '$') {
    $varName = substr($baz, 1);
    if (isset($$varName)) {
        $baz = $$varName;
    }
}

Answer 2

The is_string PHP function is used to check if a value is a string. This could be used within an if () statement to treat strings in one way and non-strings in another. It will return true or false.

 <?php 
 if (is_string(23)) 
 {
 echo "Yes";
 } else {
 echo "No";
 }
 ?>

The code above should output "No" because 23 is not a string. Let's try this again:

 <?php 
 if (is_string("Hello World")) 
 {
 echo "Yes";
 } else {
 echo "No";
 }
 ?>

Since "Hello World" is a string, this would echo "Yes".