Instead of inventing own functions in case you'd like to use array keys as placeholder names and replace corresponding array values in a string, just use the str_replace:

$string = 'Hello %name!';
$data = array(
  '%name' => 'John'
);

$greeting = str_replace(array_keys($data), array_values($data), $string);

<?php
/**
 * Like vsprintf, but accepts $args keys instead of order index.
 * Both numeric and strings matching /[a-zA-Z0-9_-]+/ are allowed.
 *
 * Example: vskprintf('y = %y$d, x = %x$1.1f', array('x' => 1, 'y' => 2))
 * Result:  'y = 2, x = 1.0'
 *
 * $args also can be object, then it's properties are retrieved
 * using get_object_vars().
 *
 * '%s' without argument name works fine too. Everything vsprintf() can do
 * is supported.
 *
 * @author Josef Kufner <jkufner(at)gmail.com>
 */
function vksprintf($str, $args)
{
    if (is_object($args)) {
        $args = get_object_vars($args);
    }
    $map = array_flip(array_keys($args));
    $new_str = preg_replace_callback('/(^|[^%])%([a-zA-Z0-9_-]+)\$/',
            function($m) use ($map) { return $m[1].'%'.($map[$m[2]] + 1).'$'; },
            $str);
    return vsprintf($new_str, $args);
}
?>

<?php
/**
 * Return a formatted string like vsprintf() with named placeholders.
 *
 * When a placeholder doesn't have a matching key in `$args`,
 *   the placeholder is returned as is to see missing args.
 * @param string $format
 * @param array $args
 * @param string $pattern
 * @return string
 */
function p($format, array $args, $pattern="/\{(\w+)\}/") {
    return preg_replace_callback($pattern, function ($matches) use ($args) {
        return @$args[$matches[1]] ?: $matches[0];
    }, $format);
}

$args = ["database"=>"people", "user"=>"staff", "pass"=>"pass123", "host"=>"localhost"];

// With PHP-like placeholders: the variable is embedded in a string "{$database}" but without the dollar sign
$format = <<<SQL
CREATE DATABASE IF NOT EXISTS {database};
GRANT ALL PRIVILEGES ON {database_name}.* TO '{user}'@'{host}';
SET PASSWORD = PASSWORD('{pass}');
SQL;
echo p($format, $args);
/*
Result:

CREATE DATABASE IF NOT EXISTS people;
GRANT ALL PRIVILEGES ON {database_name}.* TO 'staff'@'localhost';
SET PASSWORD = PASSWORD('pass123');

The `{database_name}` placeholder doesn't exist as a matching key in `$args` so it's returned as is.
*/

// With Ruby-like placeholders
$format = <<<SQL
CREATE DATABASE IF NOT EXISTS :database;
GRANT ALL PRIVILEGES ON :database_name.* TO ':user'@':host';
SET PASSWORD = PASSWORD(':pass');
SQL;
echo p($format, $args, "/:(\w+)/");
/*
Result:

CREATE DATABASE IF NOT EXISTS people;
GRANT ALL PRIVILEGES ON :database_name.* TO 'staff'@'localhost';
SET PASSWORD = PASSWORD('pass123');

The `:database_name` placeholder doesn't exist as a matching key in `$args` so it's returned as is.
*/

Note that this function now throws an ValueError* as of PHP 8.0 if there is an error:

$ php -r 'var_dump(vsprintf("%d", []));'
> Fatal error: Uncaught ValueError: The arguments array must contain 1 items, 0 given in Command line code:1

*ValueError is new in PHP 8.0, so if you want to make your code compatible to PHP 7.x you should test that the arguments array has the correct length.

This can be used for quick and dirty internationalization:

<?php
$GLOBALS['strings']['example'] = "There are %d people.";

// Loads a phrase from the translations list in lang/$lang/phrases.php
function t() {
    $args = func_get_args();
    $nArgs = func_num_args();
    
    $phrase = array_shift($args);
    $nArgs--;
    
    include_once("../lang/" . lang() . "/phrases.php");
    if (isset($GLOBALS['strings'][$phrase])) {
        return vsprintf($GLOBALS['strings'][$phrase], $args);
    } else {
        return '<span style="color: #ff0000">Untranslated string: ' . $phrase . '</span>';
    }
}
?>

vnsprintf is equal to vsprintf except for associative, signed or floating keys.

vnsprintf supports for example "%assocKey$05d", "%-2$'+10s" and "%3.2$05u", vsprintf doesn't

vnsprintf( '%2$d', $array) [2nd value] is equal to vsprintf( '%2$d', $array) [2nd value]
vnsprintf( '%+2$d', $array) [key = 2] is equal to vnsprintf( '%2.0$d', $array) [key = 2]
vnsprintf( '%+2$d', $array) [key = 2] is different of vsprintf( '%+2$d', $array) [unsupported]

When you use signed or floating keys, vnsprintf searchs for the signed truncated key of the original array

Note¹: vnsprintf does not support for example "%someKeyf" (floating number, key = someKey) or "%+03d" (signed decimal number, key = 3), you should use "%someKey$f" or "%+03$d" respectively.
Note²: "%+03d" (or "%1$+03d") will be interpreted as signed zero-padded decimal number

<?php
function vnsprintf( $format, array $data)
{
    preg_match_all( '/ (?<!%) % ( (?: [[:alpha:]_-][[:alnum:]_-]* | ([-+])? [0-9]+ (?(2) (?:\.[0-9]+)? | \.[0-9]+ ) ) ) \$ [-+]? \'? .? -? [0-9]* (\.[0-9]+)? \w/x', $format, $match, PREG_SET_ORDER | PREG_OFFSET_CAPTURE);
    $offset = 0;
    $keys = array_keys($data);
    foreach ( $match as &$value )
    {
        if ( ( $key = array_search( $value[1][0], $keys) ) !== FALSE || ( is_numeric( $value[1][0]) && ( $key = array_search( (int)$value[1][0], $keys) ) !== FALSE ) ) {
            $len = strlen( $value[1][0]);
            $format = substr_replace( $format, 1 + $key, $offset + $value[1][1], $len);
            $offset -= $len - strlen( $key);
        }
    }
    return vsprintf( $format, $data);
}

$examples = array(
    2.8=>'positiveFloat',    // key = 2 , 1st value
    -3=>'negativeInteger',    // key = -3 , 2nd value
    'my_name'=>'someString'    // key = my_name , 3rd value
);

echo vsprintf( "%%my_name\$s = '%my_name\$s'\n", $examples);    // [unsupported]
echo vnsprintf( "%%my_name\$s = '%my_name\$s'\n", $examples);    // output : "someString"

echo vsprintf( "%%2.5\$s = '%2.5\$s'\n", $examples);        // [unsupported]
echo vnsprintf( "%%2.5\$s = '%2.5\$s'\n", $examples);        // output : "positiveFloat"

echo vsprintf( "%%+2.5\$s = '%+2.5\$s'\n", $examples);        // [unsupported]
echo vnsprintf( "%%+2.5\$s = '%+2.5\$s'\n", $examples);        // output : "positiveFloat"

echo vsprintf( "%%-3.2\$s = '%-3.2\$s'\n", $examples);        // [unsupported]
echo vnsprintf( "%%-3.2\$s = '%-3.2\$s'\n", $examples);        // output : "negativeInteger"

echo vsprintf( "%%2\$s = '%2\$s'\n", $examples);            // output : "negativeInteger"
echo vnsprintf( "%%2\$s = '%2\$s'\n", $examples);            // output : [= vsprintf]

echo vsprintf( "%%+2\$s = '%+2\$s'\n", $examples);        // [unsupported]
echo vnsprintf( "%%+2\$s = '%+2\$s'\n", $examples);        // output : "positiveFloat"

echo vsprintf( "%%-3\$s = '%-3\$s'\n", $examples);        // [unsupported]
echo vnsprintf( "%%-3\$s = '%-3\$s'\n", $examples);        // output : "negativeInteger"
?>

Please note: The same functionality (sortof) can be attained between version 4.0.4 and 4.1.0 using call_user_func_array.

Example:

call_user_func_array("sprintf", $arg)

First element of $arg is the format. This rescued me in a situation where version 4.1.0 wasn't available.

Using a heredoc with vprintf:

<?php
$string = <<<THESTRING
I like the state of %1\$s <br />
I picked: %2\$d as a number, <br />
I also picked %2\$d as a number again <br />
%3\$s<br />
THESTRING;

$returnText = vprintf(  $string, array('Oregon','7','I Love Oregon')  );

echo $returnText;
?>

MessageFormatter::formatMessage(string $locale, string $pattern, array $values)

or 

msgfmt_format_message(string $locale, string $pattern, array $values)

can be an alternativ option:

$values = ['rank'=>10, 'name'=>'Frank']

MessageFormatter::formatMessage('en', 'Hello {name}, your rank is {rank}', $values);

Also access by index is possible "{1}", formating and a lot more.

https://unicode-org.github.io/icu/userguide/format_parse/numbers/

vsprintf() accepts arrays with any keys, so the array_shift() technique is unnecessary when writing a printf-type function. Any parameters you require are easily unset from the array you retrieve with func_get_args():

<?php

function mysprintf($format) {
    $args = func_get_args();
    unset($args[0]); /* get rid of "$format" */
    return vsprintf($format, $args);
}

/* I use this technique in production code as follows: */
function logf($target, $string) {
    $args = func_get_args();
    unset($args[0], $args[1]);
    fprintf($GLOBALS['config']['logtargets'][$target],
        "[%s] %s\n", date('H:i'), wordwrap(vsprintf($string, $args), 75, '\n\r '));
}

/* e.g.:
    logf(DEBUG, "Oops! %s", mysql_error());
 */

?>

array_shift() and other costly array operations aren't required, as far as I know. I could be wrong.

It's necessary to clearly how to apply argument swapping when using an array of arguments. One might be tempted to use %0$ to reference $args[0].

In reality, the position specifier is always the array index+1:

$args[0]  is referenced by %1$...
$args[1]  is referenced by %2$... 
etc.

Similarly, the first subpattern of a RegEx match would be found in $matches[1], the second in $match[2], etc. However if the $matches array is used as arguments to vsprint(), then the position specifier is subpattern+1:

preg_match( $pattern, $subject, $matches );
vsprintf( 'Full Match = %1$s, first Subpattern = %2$s, second Subpattern = %3$s', $matches );