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);

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.

<?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.
*/

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 );