Docker to run multiple PHP versions

When programming, I like to have the tools on my current shell. I use PHP 8 on a daily basis but from times to times you need to test something with older versions. Docker is really handy for this and I usually use a Dockerfile like this:

# change the version here
FROM php:7.4-alpine
COPY --from=composer /usr/bin/composer /usr/bin/composer
RUN apk add git bash 
CMD ["php"]

Once you have this, build and run:

docker build -t php-tool .
docker run --tty --detach --rm --name php -v "$PWD:/srv" php-tool
# or
docker run -t -d --rm --name php -v "$PWD:/srv" php-tool

For the run command we allocate a pseudo tty (using -t or --tty) to keep the php process open (as it will act as REPL). Combine that to -d, --detach and you’ll have a docker container running under the name of php. /srv is the workdir and I binded the current $PWD (print working directory) to that location. Now to use it, either start a shell using bash and -t with -i (--interactive to keep stdin open):

docker exec -ti php bash

bash-5.1# php --version
PHP 7.4.16 (cli) (built: Mar  6 2021 04:24:10) ( NTS )
Copyright (c) The PHP Group
Zend Engine v3.4.0, Copyright (c) Zend Technologies

Or run scripts:

docker exec -t php composer update

Note that I strongly suggest to remove the vendor directory as symbolink links may have been destroyed in the volume-bind process (using simple-php-unit for example).