Wordpress: Variable Unbound Error: When adding a custom entrypoint that uses the original docker-entrypoint.sh

[myuseringithub]

Official Wordpress "docker-entrypoint.sh" is run from a custom shell script, throughs an error:
/usr/local/bin/docker-entrypoint.sh: line 26: $1: unbound variable
Line points to:
if [[ "$1" == apache2* ]] || [ "$1" == php-fpm ]; then in https://github.com/docker-library/wordpress/blob/master/docker-entrypoint.sh

Steps to reproduce:

• Add a custom entrypoint to docker-compose.yml (after adding the file to container /usr/local/bin/custom-entrypoint.sh using the Dockerfile):
  ... entrypoint: custom-entrypoint.sh
  Contents of custom-entrypoint.sh:

sed -i -e 's/^exec "$@"/#exec "$@"/g' /usr/local/bin/docker-entrypoint.sh
source docker-entrypoint.sh
exec "$@"

• Build & Run the error will appear, although it is the exact same shell from the official repository, what's different ?

[tianon]

What's different is the arguments provided -- in the image as-is, we don't run docker-entrypoint.sh by itself, but rather pass apache2-foreground or php-fpm to it (depending on which variant we're using). So the final command is something more like docker-entrypoint.sh apache2-foreground.

[myuseringithub]

That what I was missing... Thanks ! I ended up forking the dockerfile and related docker-entrypoint.sh, and added what I need.
Can you explain to me in simple words what this gibberish means:
sed -i -e 's/^exec "$@"/#exec "$@"/g' /usr/local/bin/docker-entrypoint.sh although I'm no longer using it, had a hard time understanding it. Where does it search for exec in ? what does it replace ? Why ?

[tianon]

That line searches for a line that starts with exec "$@" in the existing entrypoint script and comments it out so that it doesn't run. That exec line will actually _run_ the arguments to the script after it executes, rather than simply running the initialization steps.

[myuseringithub]

Oh.. simple way of extending the shell script. Thanks

[jfahrenkrug]

Just some background info for others who find this thread:
The basic problem is that if the base image defines BOTH CMD and ENTRYPOINT, your image also has to override both. You can't just override ENTRYPOINT and then keep/inherit CMD. The docs say:

Note: If CMD is defined from the base image, setting ENTRYPOINT will reset CMD to an empty value. In this scenario, CMD must be defined in the current image to have a value.

Source: https://docs.docker.com/engine/reference/builder/#entrypoint