How to call a function interpolated in string?

If you're calling a method of some class, you can use normal variable expansion. For example:

<?php
class thingie {

  public function sayHello() {
    return "hello";
  }

}

$t = new thingie();
echo "thingie says: {$t->sayHello()}";

This will output:

thingie says: hello

Note that the braces around the call are required.

function foo()
{
    return 'Hi';
}
$my_foo = 'foo';
echo "{$my_foo()}";

Just use this:

$str = "abcdefg".foo()."hijklmnopqrstuvwxyz";

It will call function during string creation.

$foo = foo();
$str = "abcdefg {$foo} hijklmopqrst";

Short answer: No.

No. There is no such native construct to call functions like "Date is: date() yeah yeah" and processing such string sounds like a performance nightmare, and a security nightmare.

Good news: you may really just use printf() or sprintf():

<?php
printf(
    'Year is: %s, and month is: %s',
    date('Y'),
    date('m')
);

Output:

Year is: 2025, and month is: 09

Documentation about printf:

https://www.php.net/sprintf

Long answer: Well... Yes. There is This Hack

Well. Yes. If you really need to get arbitrary expressions being evaluated from a double-quoted string, you can implement a workaround, speculating on a feature called variable-functions:

<?php
/**
 * Hack to dynamically process things inside strings.
 *
 * @param mixed $v Value
 * return mixed Same value
 */
$GLOBALS['_'] = function ($v) {
    return $v;
};


// Happy hacking in global context
echo "Year is: {$_(date('Y'))} and the max function returns {$_(max( 1, 2, 3 ))}...{$_(str_repeat(' arrh', 3))}! ";

// Happy hacking inside functions
function test() {
    global $_;
    echo "Also works in functions! Here random: {$_(random_int(0, 10))}. Yeah!";
}
test();

Result:

Year is 2025 and the max function returns 3... arrh arrh arrh!
Also works in functions! Here random: 8. Yeah!

The example is not limited to date(), max() and str_repeat(): you can surely define your own functions like foo() and just call them, as long as they return a valid string.

This example creates a simple global variable called just $_ and this name is adopted just to be very very short, so you type less. This variable contains a simple function which just returns the first argument. This is syntax sugar for you, since functions are not easily expanded as-is inside a string. Instead, variables are expanded easily. That's it.

I wonder if PHP will ever introduce a native feature to do that (note: I've written this note in 2018). In the meanwhile, this is the only workaround.

References:

• https://secure.php.net/manual/en/functions.variable-functions.php
• https://secure.php.net/manual/it/language.types.string.php#language.types.string.parsing

Limitations of This Hack

Note that, with this hack, the functions are immediately expanded when you define the string. So, do not expect to store the string in a variable and see the result changed every time you print it.

Another reason why you should not use this hack, is that it's not compatible with many internationalization workflows. For example it's not compatible with GNU Gettext.

Its still not possible, There are hacks available but not what I would recommend rather suggest to stick with old school dot operator i.e. $str="abcdefg ". foo() ." hijklmopqrst";

As per the Complex (curly) syntax documentation

Note:
Functions, method calls, static class variables, and class constants inside {$} work since PHP 5. However, the value accessed will be interpreted as the name of a variable in the scope in which the string is defined. Using single curly braces ({}) will not work for accessing the return values of functions or methods or the values of class constants or static class variables.

<? 
function foo($b)
{
    return "Hi $b";
}
$bar = 'bario';


$my_foo = 'foo';
echo "<br>1 {$my_foo($bar)}"; 

$myfoo = foo; // my 'version'
echo "<br>2 {$myfoo($bar)}"; 

// the following is nogo; php error! $myfoo can not be called as function because it got the return value if foo() which is a string.
// means https://stackoverflow.com/users/517676/savinger answer above is wrong; this program doesn't print "<br>end":
 
$myfoo = foo();
echo "<br>3 {$myfoo($bar)}"; 

echo "<br>end";
?>

The output is:

1 Hi bario
2 Hi bario