Why this page exists: PHP
Here you can try PHP in a constrained runner that favors clarity over project setup. The work area is meant for quick edits, quick failures, and quick confirmation when a language rule is fuzzy.
Runs PHP through Piston from main.php, so examples execute like CLI PHP rather than through Apache or PHP-FPM. The page returns output after the runner or preview finishes, which is usually only a few seconds for the kind of examples that belong here.
Superglobals such as $_GET and $_POST do not appear by magic in a CLI-style run. We would rather be blunt about that limit than make the page sound bigger than it is.
Concrete example
The saved example below is intentionally left unchanged. Run it once as written, then make a small edit and run it again; that gives you a known-good baseline before you test your own idea.
<?php
$name = trim(fgets(STDIN));
$upper = strtoupper($name);
$length = strlen($name);
echo "Hello, $upper! Your name has $length characters.\n";The next preserved block belongs to the same example. Keep it nearby when you are comparing input, output, or the shape of the result. Small examples expose mistakes quickly.
Hello, ALICE! Your name has 5 characters.After the sample works, try one edge case that exercises the page's limits. Superglobals such as $_GET and $_POST do not appear by magic in a CLI-style run. That single change often teaches more than pasting a large program and trying to guess which part failed.
Behind the scenes
The useful part is the turnaround. Write code in the page editor, provide STDIN or arguments if the page exposes those controls, and press Run.
The page packages the source and input, sends them to the configured runner or preview frame, and prints standard output plus errors in the output area. Short path. Useful signal.
When something fails, read the first error before changing the whole snippet; many compiler messages are noisy at the bottom but precise near the top, especially when a missing bracket causes a chain of follow-up complaints.
If the first run succeeds, resist the urge to paste the whole project next. Add one feature, one input case, or one PHP construct at a time, because a runner like this is best at showing the exact moment a simple idea stops being simple.
What it cannot prove
The runner is not a production environment. It will not carry durable state between serious sessions, and it should not be asked to handle Composer packages, sessions, uploaded files, databases, and web-server configuration. Good. Boundaries make bugs easier to see.
The sweet spot is arrays, loops, string handling, JSON encoding, and function sketches. If your example needs a package manager, a database full of private rows, a web server listening on a port, or special build flags, move it to a local workspace before you draw conclusions.
A small runner should feel disposable. Try the idea, keep the useful lesson, and leave the accidental environment behind when the next step needs real project context.
Practical uses
Three uses come up often: checking syntax while reading docs, reducing a bug report to something another person can run, and trying a small variation before editing a larger project.
For PHP, the best examples are boring in a useful way. They fit on one screen, they name the input, and they show the exact output you expected or the exact error you got.
A good habit is to keep one saved version that passes, then make the risky change in a copy. When the output changes, you know which line caused it; when it does not, you have learned that the bug probably lives in setup, data, or assumptions rather than the syntax itself.
Questions from the editor
This FAQ is intentionally mixed: short answers for quick checks, longer notes where PHP has environment traps. Scan it once before assuming the runner and your local setup behave the same.
What does a PHP compiler do?
PHP is usually compiled to opcodes by the PHP engine, then executed. In production, OPcache can keep those opcodes around so repeated requests are faster. For this page, think of it as CLI PHP: write a small script, run it, and inspect printed output or errors. For example, php main.php runs a command-line PHP script. This is CLI-style PHP, not a full web request, so superglobals and sessions should not be treated like a live server.
Is there a free PHP compiler?
Yes, you can use this page for free PHP practice. It is good for arrays, strings, loops, functions, JSON encoding, and quick syntax checks. Do not paste secrets or database credentials. If you need Composer packages, web-server behavior, sessions, or uploads, test in a local PHP project. This is CLI-style PHP, not a full web request, so superglobals and sessions should not be treated like a live server.
How to compile PHP code?
Most PHP code is not compiled manually. You save a .php file and run it with php file.php or serve it through a web server. The engine handles parsing and opcode generation. Packaging tools exist, but they are not the normal workflow for learning or testing small PHP scripts. For example, php main.php runs a command-line PHP script. This is CLI-style PHP, not a full web request, so superglobals and sessions should not be treated like a live server.
Is PHP a compiled or interpreted language?
PHP is often called interpreted, but the engine parses code and turns it into opcodes before execution. With OPcache, those opcodes can be reused in server environments. So the honest answer is mixed: you usually run PHP scripts directly, while the engine handles compilation details behind the scenes. This is CLI-style PHP, not a full web request, so superglobals and sessions should not be treated like a live server.
How does the PHP compiler work?
The PHP engine reads the source, checks syntax, builds internal opcodes, and executes them. In a web app, OPcache may store those opcodes between requests. In this online runner, you mainly see the practical result: syntax errors, runtime warnings, printed output, and behavior of core language functions. For example, php main.php runs a command-line PHP script. This is CLI-style PHP, not a full web request, so superglobals and sessions should not be treated like a live server.
Version?
This page runs PHP through Piston using main.php; the wildcard version means the runner supplies its available php runtime. I would treat that as good enough for syntax checks, but not as a promise about your production version. If a feature depends on a release, run the same snippet locally and check the official release notes. Version mismatches usually show up as syntax errors, missing APIs, or slightly different standard-library behavior.
Can I use packages with PHP?
Assume package installs are not available here unless the page already loads a library for the demo. That keeps the run predictable and quick. If your example needs a package manager, create a local project and add the dependency there, then use this page only for the small language part. For online testing, replace the dependency call with a tiny mock value and test your own logic around it.
Show me stdin.
Use the STDIN box for the text your program would normally read from the terminal. Put one input value per line. For example, enter Alice on the first line and 42 on the second, then read two values in your code. If parsing fails, test one line first before adding more cases. This is especially helpful for coding-challenge style problems where input shape causes most mistakes.
Documentation
Reference pages are better than folklore when an error message gets specific. Start with official docs, then use tutorials for context once the rule is clear.