Docker

A keyword is found immediately following a #. In order for the # to start a comment, it needs to come after a word boundary such as a space.

This warning is triggered when an unquoted literal string is found suspiciously sandwiched between two double quoted strings.

Unlike Perl or PHP, $ is not used when assigning to a variable.

You can never rely on the assumption that the latest tag points to a specific version of an image. Explicitly tagging the image with a specific version (e.g. ubuntu:12.04) ensures that your application will not break due to random changes across different versions of an image you depend on.

Version pinning forces the build to retrieve a particular version regardless of what’s in the cache. This technique can also reduce failures due to unanticipated changes changes between different versions in required packages.

== is being used in an unexpected way. The two most common reasons for this is: - You wanted to assign a value but accidentally used == instead of =.

By using absolute paths you will not run into problems when a previous WORKDIR instruction changes. You also often don't know the WORKDIR context of your base container.

For some POSIX commands it makes no sense to run them in a Docker container because they are bound to the host or are otherwise dangerous (like ´shutdown´, ´service´, ´ps´, ´free´, ´top´, ´kill´, ´mount´, ´ifconfig´). Interactive utilities also don't make much sense (´nano´, ´vim´).

Using the latest tag can cause breakages when a new version of an image is released. You can never rely on the assumption that the latest tag points to a specific version of an image.

Without the -y/--assume-yes option it might be possible for the build to break without human intervention.

Trying to copy from a missing image alias results in an error.

Trying to copy from the same image the instruction is running in results in an error.

Defining duplicate stage names results in an error.

If you list more than one ENTRYPOINT then only the last ENTRYPOINT command will be setup, making prior ENTRYPOINT setups redundant.

Shells differ widely in how they handle unescaped parentheses in eval expressions. eval foo=bar is allowed by dash, bash and ksh.

The for loop expects the variable's name, not its value (and the name can not be specified indirectly).

As of Alpine Linux 3.3 there exists a new --no-cache option for apk. It allows users to install packages with an index that is updated and used on-the-fly and not cached locally: This avoids the need to use --update and remove /var/cache/apk/* when done installing packages.