When multiple PHP installations exist on a system (like /usr/local/bin/php and /usr/local/bin/php5), determine the active version with these methods:

# Basic version check
php -v

# Locate the PHP binary path
which php
# or
command -v php

# For detailed configuration path
php -i | grep 'Configuration File'

Create a test file (info.php) with this content:

<?php
phpinfo();
?>

Access it via browser to see:

• Loaded configuration file path
• PHP binary location
• All active extensions

Run this script to output execution details:

<?php
echo "PHP Binary: " . PHP_BINARY . "\n";
echo "Include Path: " . get_include_path() . "\n";
echo "Loaded Config: " . php_ini_loaded_file() . "\n";
?>

When using alternatives system (common in Linux):

# List all available PHP versions
update-alternatives --list php

# Manually switch versions
sudo update-alternatives --config php

For web applications, verify which PHP processor is active:

# For Apache
apachectl -M | grep php

# For Nginx + PHP-FPM
ps aux | grep php-fpm

When multiple PHP installations exist on a system (e.g., /usr/local/bin/php and /usr/local/bin/php5), determining the actual PHP interpreter being used requires several diagnostic approaches. This is particularly important for:

• Debugging version-specific behaviors
• Ensuring compatibility with frameworks
• Validating CLI vs web server environments

The most comprehensive way to check your active PHP configuration:

<?php
// Create a test file named phpinfo.php
phpinfo();
?>

Access this via web browser and check:

• "Loaded Configuration File" path
• "Configuration File (php.ini) Path"
• Top-line version information

For CLI scripts, use these terminal commands:

# Check default PHP path
which php

# Verify executable path
readlink -f $(which php)

# Get version details
php -v
php -i | grep "Loaded Configuration File"

Create a diagnostic script:

<?php
echo "Executable path: " . PHP_BINARY . "\n";
echo "Include path: " . get_include_path() . "\n";
echo "php.ini location: " . php_ini_loaded_file() . "\n";

For Apache/Nginx environments:

# Apache
grep -i "php" /etc/apache2/sites-enabled/*.conf

# Nginx
grep -i "fastcgi_pass" /etc/nginx/sites-enabled/*

Common handler patterns:

• mod_php: LoadModule php_module
• PHP-FPM: fastcgi_pass unix:/run/php/phpX.X-fpm.sock
• CGI: Action application/x-httpd-php

When using version managers:

# For phpbrew
phpbrew list

# For update-alternatives
update-alternatives --list php