Use of increment operator in heredoc

Question

I want to increase the value of a variable by using the increment operator in heredoc. My current code is given below...

$counter = 0;
for($i = 0; $i<10; $i++):
echo <<< EOT
    $counter++ <br/>
EOT;
endfor;

Its output is...

0++
0++
.
.

Mean post-increment operator is not working.

I have also tried pre-increment, like given below...

echo <<< EOT
   ++$counter <br/>
EOT;

Its output is...

++0
++0
.
.

Mean pre-increment operator is also not working.

I have also tried to put increment operation inside curly braces, like given below...

echo <<< EOT
    {++$counter} <br/>
EOT;

But again no luck. Output is....

{++0} 
{++0} 
.
.

I have also searched it on google but didn't find anything useful.

I know if I can increase value before heredoc then I can print it in here doc correctly

$counter = 0;
for($i = 0; $i<10; $i++):
++$counter;
echo <<< EOT
    $counter <br/>
EOT;
endfor;

It works fine.

But I want to use increment operator in heredoc, just like we use in case of single or double quoted with echo .

But it seems like heredoc doesn't support increment operation.

Answer 1

The complex/curly variable syntax {$var…} does only allow variable access expressions, but not PHP expressions per se.

• For example {$var[…]}
• Or {$var(…)}
• And {$var->prop…}
• And {${stat::$lookup}}

There can't be arithmetic operators within the { + } itself. But only between […] or (…) used alongside.

One common workaround is to utilize variable function names:

$func = "htmlspecialchars";  // or any other no-op function
echo <<<HEREDOC
    counter = {$func($counter++)}
HEREDOC;

Where you can easily use full expressions in the curly var syntax.