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+# PHP {#sec-php}
+
+## User Guide {#ssec-php-user-guide}
+
+### Overview {#ssec-php-user-guide-overview}
+
+Several versions of PHP are available on Nix, each of which having a
+wide variety of extensions and libraries available.
+
+The different versions of PHP that nixpkgs provides are located under
+attributes named based on major and minor version number; e.g.,
+`php74` is PHP 7.4.
+
+Only versions of PHP that are supported by upstream for the entirety
+of a given NixOS release will be included in that release of
+NixOS. See [PHP Supported
+Versions](https://www.php.net/supported-versions.php).
+
+The attribute `php` refers to the version of PHP considered most
+stable and thoroughly tested in nixpkgs for any given release of
+NixOS - not necessarily the latest major release from upstream.
+
+All available PHP attributes are wrappers around their respective
+binary PHP package and provide commonly used extensions this way. The
+real PHP 7.4 package, i.e. the unwrapped one, is available as
+`php74.unwrapped`; see the next section for more details.
+
+Interactive tools built on PHP are put in `php.packages`; composer is
+for example available at `php.packages.composer`.
+
+Most extensions that come with PHP, as well as some popular
+third-party ones, are available in `php.extensions`; for example, the
+opcache extension shipped with PHP is available at
+`php.extensions.opcache` and the third-party ImageMagick extension at
+`php.extensions.imagick`.
+
+### Installing PHP with extensions {#ssec-php-user-guide-installing-with-extensions}
+
+A PHP package with specific extensions enabled can be built using
+`php.withExtensions`. This is a function which accepts an anonymous
+function as its only argument; the function should accept two named
+parameters: `enabled` - a list of currently enabled extensions and
+`all` - the set of all extensions, and return a list of wanted
+extensions. For example, a PHP package with all default extensions and
+ImageMagick enabled:
+
+```nix
+php.withExtensions ({ enabled, all }:
+  enabled ++ [ all.imagick ])
+```
+
+To exclude some, but not all, of the default extensions, you can
+filter the `enabled` list like this:
+
+```nix
+php.withExtensions ({ enabled, all }:
+  (lib.filter (e: e != php.extensions.opcache) enabled)
+  ++ [ all.imagick ])
+```
+
+To build your list of extensions from the ground up, you can simply
+ignore `enabled`:
+
+```nix
+php.withExtensions ({ all, ... }: with all; [ imagick opcache ])
+```
+
+`php.withExtensions` provides extensions by wrapping a minimal php
+base package, providing a `php.ini` file listing all extensions to be
+loaded. You can access this package through the `php.unwrapped`
+attribute; useful if you, for example, need access to the `dev`
+output. The generated `php.ini` file can be accessed through the
+`php.phpIni` attribute.
+
+If you want a PHP build with extra configuration in the `php.ini`
+file, you can use `php.buildEnv`. This function takes two named and
+optional parameters: `extensions` and `extraConfig`. `extensions`
+takes an extension specification equivalent to that of
+`php.withExtensions`, `extraConfig` a string of additional `php.ini`
+configuration parameters. For example, a PHP package with the opcache
+and ImageMagick extensions enabled, and `memory_limit` set to `256M`:
+
+```nix
+php.buildEnv {
+  extensions = { all, ... }: with all; [ imagick opcache ];
+  extraConfig = "memory_limit=256M";
+}
+```
+
+#### Example setup for `phpfpm` {#ssec-php-user-guide-installing-with-extensions-phpfpm}
+
+You can use the previous examples in a `phpfpm` pool called `foo` as
+follows:
+
+```nix
+let
+  myPhp = php.withExtensions ({ all, ... }: with all; [ imagick opcache ]);
+in {
+  services.phpfpm.pools."foo".phpPackage = myPhp;
+};
+```
+
+```nix
+let
+  myPhp = php.buildEnv {
+    extensions = { all, ... }: with all; [ imagick opcache ];
+    extraConfig = "memory_limit=256M";
+  };
+in {
+  services.phpfpm.pools."foo".phpPackage = myPhp;
+};
+```
+
+#### Example usage with `nix-shell` {#ssec-php-user-guide-installing-with-extensions-nix-shell}
+
+This brings up a temporary environment that contains a PHP interpreter
+with the extensions `imagick` and `opcache` enabled:
+
+```sh
+nix-shell -p 'php.withExtensions ({ all, ... }: with all; [ imagick opcache ])'
+```
+
+### Installing PHP packages with extensions {#ssec-php-user-guide-installing-packages-with-extensions}
+
+All interactive tools use the PHP package you get them from, so all
+packages at `php.packages.*` use the `php` package with its default
+extensions. Sometimes this default set of extensions isn't enough and
+you may want to extend it. A common case of this is the `composer`
+package: a project may depend on certain extensions and `composer`
+won't work with that project unless those extensions are loaded.
+
+Example of building `composer` with additional extensions:
+```nix
+(php.withExtensions ({ all, enabled }:
+  enabled ++ (with all; [ imagick redis ]))
+).packages.composer
+```
+
+### Overriding PHP packages {#ssec-php-user-guide-overriding-packages}
+
+`php-packages.nix` form a scope, allowing us to override the packages defined within. For example, to apply a patch to a `mysqlnd` extension, you can simply pass an overlay-style function to `php`’s `packageOverrides` argument:
+
+```nix
+php.override {
+  packageOverrides = final: prev: {
+    extensions = prev.extensions // {
+      mysqlnd = prev.extensions.mysqlnd.overrideAttrs (attrs: {
+        patches = attrs.patches or [] ++ [
+          …
+        ];
+      });
+    };
+  };
+}
+```