php -d: override a php.ini setting for one run (memory_limit, display_errors)

php -d memory_limit=512M script.php runs the script as if php.ini contained memory_limit = 512M. The option sets any ini directive for that one process, overriding the loaded php.ini, and can be repeated: php -d display_errors=1 -d error_reporting=E_ALL test.php. It is the quickest fix for a CLI job that dies with Allowed memory size exhausted, and for testing a setting before editing php.ini.

Effect of -d

The example uses PHP 8.4 compiled to WebAssembly (php-wasm, from the WordPress Playground project), whose CLI takes the same arguments as php in a terminal:

npm init -y >/dev/null
npm install --silent --no-audit --no-fund @php-wasm/node@3.1.56 @php-wasm/universal@3.1.56 >/dev/null 2>&1
cat > php.mjs <<'JS'
// Minimal "php" command: copies *.php files into the virtual file system and runs the CLI
import fs from "node:fs";
import { PHP } from "@php-wasm/universal";
import { loadNodeRuntime } from "@php-wasm/node";
const php = new PHP(await loadNodeRuntime("8.4", { emscriptenOptions: { processId: 1 } }));
php.mkdir("/app");
for (const f of fs.readdirSync(".").filter((f) => f.endsWith(".php"))) php.writeFile(`/app/${f}`, fs.readFileSync(f));
php.chdir("/app");
const r = await php.cli(["php", ...process.argv.slice(2)]);
process.stdout.write(await r.stdoutText);
process.stdout.write(await r.stderrText);
process.exit(await r.exitCode);
JS
echo "== memory_limit"
node php.mjs -r 'echo ini_get("memory_limit"), PHP_EOL;'
node php.mjs -d memory_limit=512M -r 'echo ini_get("memory_limit"), PHP_EOL;'
node php.mjs -d memory_limit=-1 -r 'echo ini_get("memory_limit"), PHP_EOL;'
echo "== error_reporting without warnings"
node php.mjs -d 'error_reporting=E_ALL & ~E_WARNING' -r 'echo $undefined; echo "no warning shown", PHP_EOL;'
echo "== unknown directive"
node php.mjs -d no_such.setting=1 -r 'var_dump(ini_get("no_such.setting"));'
echo "== invalid value"
node php.mjs -d memory_limit=lots -r 'echo ini_get("memory_limit"), PHP_EOL;' 2>&1 | sed -n '2p'

== memory_limit
256M
512M
-1
== error_reporting without warnings
no warning shown
== unknown directive
bool(false)
== invalid value
Warning: Invalid "memory_limit" setting. Invalid quantity "lots": no valid leading digits, interpreting as "0" for backwards compatibility in Unknown on line 0

The default here (256M) comes from the php-wasm php.ini; a stock PHP build without php.ini uses 128M. -1 removes the limit. Constants such as E_ALL & ~E_WARNING are evaluated as in php.ini, so quote the value for the shell. A directive PHP does not know is ignored (ini_get returns false), and an invalid quantity produces a startup warning such as Invalid "memory_limit" setting.

Common settings for CLI runs

-d name without =value sets the directive to "1".

Order of precedence

1. Built-in defaults of the PHP binary.
2. php.ini and the files in the scan directory (see php --ini).
3. -d options on the command line.
4. ini_set() calls in the running script, for directives that may be changed at run time.

So -d beats php.ini, but a script that calls ini_set('memory_limit', '128M') lowers it again. -n skips step 2 entirely and runs with built-in defaults plus your -d values.

Pitfalls

• -d must come before the script name: in php script.php -d memory_limit=1G the option is passed to the script in $argv.
• Directives whose changeable mode is INI_SYSTEM or INI_PERDIR (for example short_open_tag) cannot be changed with ini_set(), but -d sets them because it is applied at startup.
• Settings for the web server (for example upload_max_filesize) are not affected; they live in the FPM or Apache configuration.

FAQ