PHP ob_get_flush() Function: Everything You Need to Know

As a PHP developer, you may need to retrieve the contents of the output buffer and flush it at the same time. The ob_get_flush() function is a built-in PHP function that does both in a single call: it returns the current buffer contents as a string and sends them to the next output level. This article explains how it works, what it returns, and when to reach for it instead of the other output-control functions.

What Is the ob_get_flush() Function?

Output buffering lets PHP collect everything you echo or print in memory instead of sending it straight to the browser. You start a buffer with ob_start(), write to it as usual, and then decide what to do with the captured output.

ob_get_flush() does three things in one step:

1. Gets the contents of the active (topmost) output buffer and returns them as a string.
2. Flushes those contents — sends them on to the next buffer level, or to the browser if no other level exists.
3. Closes that buffer level (one level of nesting is removed).

This makes it a convenient combination of ob_get_contents() (read) and ob_end_flush() (send + close).

Syntax

ob_get_flush(): string|false

Parameters

ob_get_flush() takes no parameters.

Return Value

The function returns the contents of the topmost output buffer as a string. If output buffering is not active (there is no buffer to flush), it returns false and raises a notice. Always start a buffer with ob_start() before calling it.

How to Use the ob_get_flush() Function

The pattern is: start a buffer, write to it, then call ob_get_flush() to capture and release it.

<?php

ob_start();
echo "This will be buffered";

// Capture the buffer, flush it to the browser, and close the level.
$output = ob_get_flush();

echo "\nCaptured copy: " . $output;

Output:

This will be buffered
Captured copy: This will be buffered

Here "This will be buffered" is collected in the buffer rather than printed immediately. ob_get_flush() returns that text (so $output now holds it) and at the same time sends it to the browser — that is why the phrase appears twice: once from the flush, once from the final echo.

If buffering is not active when you call it, you get false back:

<?php

$output = ob_get_flush(); // No ob_start() was called

var_dump($output); // bool(false)

ob_get_flush() vs. related functions

Choose ob_get_flush() when you want to both keep a copy of the buffered output (to log, inspect, or modify) and still send it to the browser. If you only need to send it, use ob_end_flush(); if you want to grab it without sending, use ob_get_clean().

Conclusion

The ob_get_flush() function retrieves the active output buffer as a string while flushing and closing it in one call. By understanding its empty parameter list, its string|false return value, and its buffer-closing behavior, you can manage output streams more precisely. To go deeper, explore ob_start() for opening buffers, ob_get_level() for checking nesting depth, and ob_flush() for flushing without closing.

Practice