devsetup1-7  Exercise 1: PHP Without a Web Server
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STEP 1: CHECK FIRST
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    command -v php            # nothing on a fresh install
    dpkg -l 'php*' | grep ^ii
    apt policy php-cli

STEP 2: INSTALL THE RIGHT PACKAGES
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    sudo apt install php-cli php-mbstring php-xml php-curl php-zip php-intl php-mysql php-sqlite3

Read apt's list of packages to be installed BEFORE confirming. It should
contain php8.4-cli, php8.4-common and the extension packages. It should NOT
contain apache2, libapache2-mod-php8.4, php8.4-fpm or php8.4-cgi.

STEP 3: VERIFY
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    php -v
    php -m | grep -Ei 'mbstring|curl|mysqli|pdo_mysql|pdo_sqlite|zip|intl'
    type -a php

Expected: PHP 8.4.x; each of the modules listed (mbstring, curl, mysqli,
pdo_mysql, pdo_sqlite, zip, intl); and a single /usr/bin/php.

Confirm no web server came along:
    dpkg -s apache2           # "package 'apache2' is not installed"
    systemctl status apache2  # "Unit apache2.service could not be found"
    ss -tlnp                  # nothing listening on port 80

STEP 4: SERVE A PAGE
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    mkdir -p ~/projects/php-demo && cd ~/projects/php-demo
    echo '<?php echo "Hello from PHP " . PHP_VERSION . " on " . gethostname();' > index.php
    php -S localhost:8000

Open http://localhost:8000. The page shows the PHP version and "devserver".
The terminal prints a line for each request. Stop with Ctrl+C.

WHY apt install php IS WRONG HERE
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The php package is a metapackage that depends on php8.4, and php8.4 depends on
ONE of: libapache2-mod-php8.4, php8.4-fpm or php8.4-cgi (plus php8.4-common).
It exists to make sure a server-side PHP interpreter is present. On a typical
system apt satisfies that requirement by installing Apache and its PHP
module, which starts a web server on a development machine that only needed
the command-line PHP.

php-cli gives you the php command, and the individual extensions give you
what projects actually need, with no web server.

WHY THIS WORKS AS AN ANSWER
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The exercise checks the result three ways (packages, modules, and the absence
of a web server) rather than assuming that a successful install means the
right install. Reading apt's plan before confirming is the habit that catches
this kind of mistake.