How to get a variable name as a string in PHP?

Say i have this PHP code:

$FooBar = "a string";

i then need a function like this:

print_var_name($FooBar);

which prints:

FooBar

Any Ideas how to achieve this? Is this even possible in PHP?

I couldn't think of a way to do this efficiently either but I came up with this. It works, for the limited uses below.

shrug

<?php

function varName( $v ) {
    $trace = debug_backtrace();
    $vLine = file( __FILE__ );
    $fLine = $vLine[ $trace[0]['line'] - 1 ];
    preg_match( "#\\$(\w+)#", $fLine, $match );
    print_r( $match );
}

$foo = "knight";
$bar = array( 1, 2, 3 );
$baz = 12345;

varName( $foo );
varName( $bar );
varName( $baz );

?>

// Returns
Array
(
    [0] => $foo
    [1] => foo
)
Array
(
    [0] => $bar
    [1] => bar
)
Array
(
    [0] => $baz
    [1] => baz
)

It works based on the line that called the function, where it finds the argument you passed in. I suppose it could be expanded to work with multiple arguments but, like others have said, if you could explain the situation better, another solution would probably work better.

You could use get_defined_vars() to find the name of a variable that has the same value as the one you're trying to find the name of. Obviously this will not always work, since different variables often have the same values, but it's the only way I can think of to do this.

Edit: get_defined_vars() doesn't seem to be working correctly, it returns 'var' because $var is used in the function itself. $GLOBALS seems to work so I've changed it to that.

function print_var_name($var) {
    foreach($GLOBALS as $var_name => $value) {
        if ($value === $var) {
            return $var_name;
        }
    }

    return false;
}

Edit: to be clear, there is no good way to do this in PHP, which is probably because you shouldn't have to do it. There are probably better ways of doing what you're trying to do.

You might consider changing your approach and using a variable variable name?

$var_name = "FooBar";
$$var_name = "a string";

then you could just

print($var_name);

to get

FooBar

Here's the link to the PHP manual on Variable variables

No-one seems to have mentioned the fundamental reasons why this is a) hard and b) unwise:

• A "variable" is just a symbol pointing at something else. In PHP, it internally points to something called a "zval", which can actually be used for multiple variables simultaneously, either because they have the same value (PHP implements something called "copy-on-write" so that $foo = $bar doesn't need to allocate extra memory straight away) or because they have been assigned (or passed to a function) by reference (e.g. $foo =& $bar). So a zval has no name.
• When you pass a parameter to a function you are creating a new variable (even if it's a reference). You could pass something anonymous, like "hello", but once inside your function, it's whatever variable you name it as. This is fairly fundamental to code separation: if a function relied on what a variable used to be called, it would be more like a goto than a properly separate function.
• Global variables are generally considered a bad idea. A lot of the examples here assume that the variable you want to "reflect" can be found in $GLOBALS, but this will only be true if you've structured your code badly and variables aren't scoped to some function or object.
• Variable names are there to help programmers read their code. Renaming variables to better suit their purpose is a very common refactoring practice, and the whole point is that it doesn't make any difference.

Now, I understand the desire for this for debugging (although some of the proposed usages go far beyond that), but as a generalised solution it's not actually as helpful as you might think: if your debug function says your variable is called "$file", that could still be any one of dozens of "$file" variables in your code, or a variable which you have called "$filename" but are passing to a function whose parameter is called "$file".

A far more useful piece of information is where in your code the debug function was called from. Since you can quickly find this in your editor, you can see which variable you were outputting for yourself, and can even pass whole expressions into it in one go (e.g. debug('$foo + $bar = ' . ($foo + $bar))).

For that, you can use this snippet at the top of your debug function:

$backtrace = debug_backtrace();
echo '# Debug function called from ' . $backtrace[0]['file'] . ' at line ' . $backtrace[0]['line'];

This is exactly what you want - its a ready to use "copy and drop in" function that echo the name of a given var:

function print_var_name(){
	// read backtrace
	$bt   = debug_backtrace();
	// read file
	$file = file($bt[0]['file']);
	// select exact print_var_name($varname) line
	$src  = $file[$bt[0]['line']-1];
	// search pattern
    $pat = '#(.*)'.__FUNCTION__.' *?\( *?(.*) *?\)(.*)#i';
	// extract $varname from match no 2
	$var  = preg_replace($pat, '$2', $src);
	// print to browser
	echo '<pre>' . trim($var) . ' = ' . print_r(current(func_get_args()), true) . '</pre>';
}

USAGE: print_var_name($FooBar)

PRINT: FooBar

> HINT
> Now you can rename the function and it will still work and also use the function several times in one line! Thanks to @Cliffordlife
> And I add a nicer output! Thanks to @Blue-Water

I made an inspection function for debugging reasons. It's like print_r() on steroids, much like Krumo but a little more effective on objects. I wanted to add the var name detection and came out with this, inspired by Nick Presta's post on this page. It detects any expression passed as an argument, not only variable names.

This is only the wrapper function that detects the passed expression. Works on most of the cases. It will not work if you call the function more than once in the same line of code.

This works fine: die(inspect($this->getUser()->hasCredential("delete")));

inspect() is the function that will detect the passed expression.

We get: $this->getUser()->hasCredential("delete")

function inspect($label, $value = "__undefin_e_d__")
{
    if($value == "__undefin_e_d__") {

        /* The first argument is not the label but the 
           variable to inspect itself, so we need a label.
           Let's try to find out it's name by peeking at 
           the source code. 
        */

        /* The reason for using an exotic string like 
           "__undefin_e_d__" instead of NULL here is that 
           inspected variables can also be NULL and I want 
           to inspect them anyway.
        */

        $value = $label;

        $bt = debug_backtrace();
        $src = file($bt[0]["file"]);
        $line = $src[ $bt[0]['line'] - 1 ];
        
        // let's match the function call and the last closing bracket
        preg_match( "#inspect\((.+)\)#", $line, $match );
        
        /* let's count brackets to see how many of them actually belongs 
           to the var name
           Eg:   die(inspect($this->getUser()->hasCredential("delete")));
                  We want:   $this->getUser()->hasCredential("delete")
        */
        $max = strlen($match[1]);
        $varname = "";
        $c = 0;
        for($i = 0; $i < $max; $i++){
            if(     $match[1]{$i} == "(" ) $c++;
            elseif( $match[1]{$i} == ")" ) $c--;
            if($c < 0) break;
            $varname .=  $match[1]{$i};
        }
        $label = $varname;
    }

    // $label now holds the name of the passed variable ($ included)
    // Eg:   inspect($hello) 
    //             => $label = "$hello"
    // or the whole expression evaluated
    // Eg:   inspect($this->getUser()->hasCredential("delete"))
    //             => $label = "$this->getUser()->hasCredential(\"delete\")"
    
    // now the actual function call to the inspector method, 
    // passing the var name as the label:

      // return dInspect::dump($label, $val);
         // UPDATE: I commented this line because people got confused about 
         // the dInspect class, wich has nothing to do with the issue here.

    echo("The label is: ".$label);
    echo("The value is: ".$value);

}

Here's an example of the inspector function (and my dInspect class) in action:

http://inspect.ip1.cc

Texts are in spanish in that page, but code is concise and really easy to understand.

Lucas on PHP.net provided a reliable way to check if a variable exists. In his example, he iterates through a copy of the global variable array (or a scoped array) of variables, changes the value to a randomly generated value, and checks for the generated value in the copied array.

function variable_name( &$var, $scope=false, $prefix='UNIQUE', $suffix='VARIABLE' ){
    if($scope) {
    	$vals = $scope;
    } else {
    	$vals = $GLOBALS;
    }
    $old = $var;
    $var = $new = $prefix.rand().$suffix;
    $vname = FALSE;
    foreach($vals as $key => $val) {
	    if($val === $new) $vname = $key;
    }
    $var = $old;
    return $vname;
}

Then try:

$a = 'asdf';
$b = 'asdf';
$c = FALSE;
$d = FALSE;

echo variable_name($a); // a
echo variable_name($b); // b
echo variable_name($c); // c
echo variable_name($d); // d

Be sure to check his post on PHP.net: http://php.net/manual/en/language.variables.php

From [php.net][1]

@Alexandre - short solution

<?php
function vname(&$var, $scope=0)
{
    $old = $var;
    if (($key = array_search($var = 'unique'.rand().'value', !$scope ? $GLOBALS : $scope)) && $var = $old) return $key;  
}
?>

@Lucas - usage

<?php
//1.  Use of a variable contained in the global scope (default):
  $my_global_variable = "My global string.";
  echo vname($my_global_variable); // Outputs:  my_global_variable

//2.  Use of a local variable:
  function my_local_func()
  {
    $my_local_variable = "My local string.";
    return vname($my_local_variable, get_defined_vars());
  }
  echo my_local_func(); // Outputs: my_local_variable

//3.  Use of an object property:
  class myclass
  {
    public function __constructor()
    {
      $this->my_object_property = "My object property  string.";
    }
  }
  $obj = new myclass;
  echo vname($obj->my_object_property, $obj); // Outputs: my_object_property
?>

[1]: http://www.php.net/manual/en/language.variables.php#49997 "php.net"

Many replies question the usefulness of this. However, getting a reference for a variable can be very useful. Especially in cases with objects and $this. My solution works with objects, and as property defined objects as well:

function getReference(&$var)
{
    if(is_object($var))
        $var->___uniqid = uniqid();
    else
        $var = serialize($var);
    $name = getReference_traverse($var,$GLOBALS);
    if(is_object($var))
        unset($var->___uniqid);
    else
        $var = unserialize($var);
    return "\${$name}";    
}
    
function getReference_traverse(&$var,$arr)
{
    if($name = array_search($var,$arr,true))
        return "{$name}";
    foreach($arr as $key=>$value)
        if(is_object($value))
            if($name = getReference_traverse($var,get_object_vars($value)))
                return "{$key}->{$name}";
}

Example for the above:

class A
{
    public function whatIs()
    {
        echo getReference($this);
    }
}

$B = 12;
$C = 12;
$D = new A;

echo getReference($B)."<br/>"; //$B
echo getReference($C)."<br/>"; //$C
$D->whatIs(); //$D

Adapted from answers above for many variables, with good performance, just one $GLOBALS scan for many

function compact_assoc(&$v1='__undefined__', &$v2='__undefined__',&$v3='__undefined__',&$v4='__undefined__',&$v5='__undefined__',&$v6='__undefined__',&$v7='__undefined__',&$v8='__undefined__',&$v9='__undefined__',&$v10='__undefined__',&$v11='__undefined__',&$v12='__undefined__',&$v13='__undefined__',&$v14='__undefined__',&$v15='__undefined__',&$v16='__undefined__',&$v17='__undefined__',&$v18='__undefined__',&$v19='__undefined__'
) {
	$defined_vars=get_defined_vars();
	
	$result=Array();
	$reverse_key=Array();
	$original_value=Array();
	foreach( $defined_vars as $source_key => $source_value){
		if($source_value==='__undefined__') break;
		$original_value[$source_key]=$$source_key;
		$new_test_value="PREFIX".rand()."SUFIX";
		$reverse_key[$new_test_value]=$source_key;
		$$source_key=$new_test_value;

	}
	foreach($GLOBALS as $key => &$value){
		if( is_string($value) && isset($reverse_key[$value])  ) {
			$result[$key]=&$value;
		}
	}
	foreach( $original_value as $source_key => $original_value){
		$$source_key=$original_value;
	}
	return $result;
}


$a = 'A';
$b = 'B';
$c = '999';
$myArray=Array ('id'=>'id123','name'=>'Foo');
print_r(compact_assoc($a,$b,$c,$myArray) );

//print
Array
(
    [a] => A
    [b] => B
    [c] => 999
    [myArray] => Array
        (
            [id] => id123
            [name] => Foo
        )

)

You could use compact() to achieve this.

$FooBar = "a string";

$newArray = compact('FooBar');

This would create an associative array with the variable name as the key. You could then loop through the array using the key name where you needed it.

foreach($newarray as $key => $value) {
    echo $key;
}

If the variable is interchangable, you must have logic somewhere that's determining which variable gets used. All you need to do is put the variable name in $variable within that logic while you're doing everything else.

I think we're all having a hard time understanding what you're needing this for. Sample code or an explanation of what you're actually trying to do might help, but I suspect you're way, way overthinking this.

I actually have a valid use case for this.

I have a function cacheVariable($var) (ok, I have a function cache($key, $value), but I'd like to have a function as mentioned).

The purpose is to do:

$colour = 'blue';
cacheVariable($colour);

...

// another session

...

$myColour = getCachedVariable('colour');

I have tried with

function cacheVariable($variable) {
   $key = ${$variable}; // This doesn't help! It only gives 'variable'.
   // do some caching using suitable backend such as apc, memcache or ramdisk
}

I have also tried with

function varName(&$var) {
   $definedVariables = get_defined_vars();
   $copyOfDefinedVariables = array();
   foreach ($definedVariables as $variable=>$value) {
      $copyOfDefinedVariables[$variable] = $value;
   }
   $oldVar = $var;
   $var = !$var;
   $difference = array_diff_assoc($definedVariables, $copyOfDefinedVariables);
   $var = $oldVar;
   return key(array_slice($difference, 0, 1, true));
}

But this fails as well... :(

Sure, I could continue to do cache('colour', $colour), but I'm lazy, you know... ;)

So, what I want is a function that gets the ORIGINAL name of a variable, as it was passed to a function. Inside the function there is no way I'm able to know that, as it seems. Passing get_defined_vars() by reference in the second example above helped me (Thanks to Jean-Jacques Guegan for that idea) somewhat. The latter function started working, but it still only kept returning the local variable ('variable', not 'colour').

I haven't tried yet to use get_func_args() and get_func_arg(), ${}-constructs and key() combined, but I presume it will fail as well.

I have this:

  debug_echo(array('$query'=>$query, '$nrUsers'=>$nrUsers, '$hdr'=>$hdr));

I would prefer this:

  debug_echo($query, $nrUsers, $hdr);

The existing function displays a yellow box with a red outline and shows each variable by name and value. The array solution works but is a little convoluted to type when it is needed.

That's my use case and yes, it does have to do with debugging. I agree with those who question its use otherwise.

Here's my solution based on Jeremy Ruten

class DebugHelper {
    
    function printVarNames($systemDefinedVars, $varNames) {
        foreach ($systemDefinedVars as $var=>$value) {
            if (in_array($var, $varNames )) {
                var_dump($var);
                var_dump($value);
            }
        }
    }
}

using it

DebugHelper::printVarNames(
	$systemDefinedVars = get_defined_vars(),
	$varNames=array('yourVar00', 'yourVar01')
);

I think you want to know variable name with it's value. You can use an associative array to achieve this.

use variable names for array keys:

$vars = array('FooBar' => 'a string');

When you want to get variable names, use array_keys($vars), it will return an array of those variable names that used in your $vars array as it's keys.

This is the way I did it

function getVar(&$var) {
    $tmp = $var; // store the variable value
    $var = '_$_%&33xc$%^*7_r4'; // give the variable a new unique value
    $name = array_search($var, $GLOBALS); // search $GLOBALS for that unique value and return the key(variable)
    $var = $tmp; // restore the variable old value
    return $name;
}

Usage

$city  = "San Francisco";
echo getVar($city); // city

Note: some PHP 7 versions will not work properly due to a bug in array_search with $GLOBALS, however all other versions will work.

See this https://3v4l.org/UMW7V

There is no predefined function in PHP that can output the name of a variable. However, you can use the result of get_defined_vars(), which returns all the variables defined in the scope, including name and value. Here is an example:

<?php
    // Function for determining the name of a variable
    function getVarName(&$var, $definedVars=null) {
        $definedVars = (!is_array($definedVars) ? $GLOBALS : $definedVars);
        $val = $var;
        $rand = 1;
        while (in_array($rand, $definedVars, true)) {
            $rand = md5(mt_rand(10000, 1000000));
        }
        $var = $rand;
         
        foreach ($definedVars as $dvName=>$dvVal) {
            if ($dvVal === $rand) {
                $var = $val;
                return $dvName;
            }
        }
         
        return null;
    }
 
    // the name of $a is to be determined.   
    $a = 1;
     
    // Determine the name of $a
    echo getVarName($a);
?>

Read more in How to get a variable name as a string in PHP?

Why don't you just build a simple function and TELL it?

/**
 * Prints out $obj for debug
 *
 * @param any_type $obj
 * @param (string) $title
 */
function print_all( $obj, $title = false )
{
	print "\n<div style=\"font-family:Arial;\">\n";
	if( $title ) print "<div style=\"background-color:red; color:white; font-size:16px; font-weight:bold; margin:0; padding:10px; text-align:center;\">$title</div>\n";
	print "<pre style=\"background-color:yellow; border:2px solid red; color:black; margin:0; padding:10px;\">\n\n";
	var_export( $obj );
	print "\n\n</pre>\n</div>\n";
}

print_all( $aUser, '$aUser' );

I was looking for this but just decided to pass the name in, I usually have the name in the clipboard anyway.

function VarTest($my_var,$my_var_name){
	echo '$'.$my_var_name.': '.$my_var.'<br />';
}

$fruit='apple';
VarTest($fruit,'fruit');

I know this is old and already answered but I was actually looking for this. I am posting this answer to save people a little time refining some of the answers.

Option 1:

$data = array('$FooBar');  

$vars = [];  
$vars = preg_replace('/^\\$/', '', $data); 
 
$varname = key(compact($vars));  
echo $varname;

Prints:

> FooBar

For whatever reason you would find yourself in a situation like this, it does actually work.

.
Option 2:

$FooBar = "a string";  

$varname = trim(array_search($FooBar, $GLOBALS), " \t.");  
echo $varname;

If $FooBar holds a unique value, it will print 'FooBar'. If $FooBar is empty or null it will print the name of the first empty or null string it finds.

It could be used as such:

if (isset($FooBar) && !is_null($FooBar) && !empty($FooBar)) {
    $FooBar = "a string";
    $varname = trim(array_search($FooBar, $GLOBALS), " \t.");
}

other use:

shrug

function varsToArrayAssoc(...$arguments){
  
    $bt   = debug_backtrace();
    $file = file($bt[0]['file']);
    $src  = $file[$bt[0]['line']-1];
    $pat = '#(.*)'.__FUNCTION__.' *?\( *?(.*) *?\)(.*)#i';
    $vars  =explode(',',substr_replace(trim(preg_replace($pat, '$2', $src)) ,"", -1));
    $result=[];
    foreach(func_get_args() as $key=>$v){
        $index=trim(explode('$',$vars[$key])[1]);
        $result[$index]=$v;
    }
    return $result;
}

$a=12;
$b=13;
$c=123;
$d='aa';

var_dump(varsToArrayAssoc($a,$b,$c,$d));

Use this to detach user variables from global to check variable at the moment.

function get_user_var_defined () 
{
    return array_slice($GLOBALS,8,count($GLOBALS)-8);     
}

function get_var_name ($var) 
{
    $vuser = get_user_var_defined(); 
    foreach($vuser as $key=>$value) 
    {
        if($var===$value) return $key ; 
    }
}

It may be considered quick and dirty, but my own personal preference is to use a function/method like this:

public function getVarName($var) {      
  $tmp = array($var => '');
  $keys = array_keys($tmp);
  return trim($keys[0]);
}

basically it just creates an associative array containing one null/empty element, using as a key the variable for which you want the name.

we then get the value of that key using array_keys and return it.

obviously this gets messy quick and wouldn't be desirable in a production environment, but it works for the problem presented.

why we have to use globals to get variable name... we can use simply like below.

    $variableName = "ajaxmint";

    echo getVarName('$variableName');

    function getVarName($name) {
        return str_replace('$','',$name);
    }

I really fail to see the use case... If you will type print_var_name($foobar) what's so hard (and different) about typing print("foobar") instead?

Because even if you were to use this in a function, you'd get the local name of the variable...

In any case, here's the reflection manual in case there's something you need in there.