The best way to get the full PHP version string

Recently, to automate building, tagging, and pushing my geerlingguy/php-apache Docker Hub image (see this issue), I needed to find a way to reliably determine the PHP major.minor.release version string. You'd think this would be simple.

Well, using Docker, I would run the image and then try:

That's great; it outputs the version right at the start. But there are a few problems here:

• The actual version is at a different place between older and newer versions of PHP
• I would have to add regex or string search code in bash to try to extract the version
• I would have to maintain regex for version matching

Basically, any automated solution I want to use and not have to spend a lot of time maintaining... I avoid regex unless it's the last resort.

Reading through the PHP docs on predefined constants, I found a really nice one: PHP_VERSION. Yay! Testing locally on my Mac:

Great! Ship it!

But wait, when I tried this in the Docker container on Debian Stretch, I got:

Nope. Gotta do regex again, not wanting to do that.

So in the end, I used a few other constants to build the string based on the major.minor.release components:

Now, why it's PHP_VERSION, then the components are PHP_[something]_VERSION... I attribute that to PHP's generally-inconsistent and annoying naming and parameter positioning insanity.

Note: If you're just wanting to compare PHP versions, or check if the installed version is greater than/equal to/less than some other version, you don't need to do all this wrangling. PHP includes a built in function version_compare() which should work even with the distro-specific version string output from constants like PHP_VERSION and PHP_VERSION_ID.