In this section, we explain the syntax or the format of Dockerfile. A Dockerfile is made up of instructions, comments, parser directives and empty lines, as shown here:
# Comment INSTRUCTION arguments
The instruction line of Dockerfile is made up of two components, where the instruction line begins with the instruction itself, which is followed by the arguments for the instruction. The instruction could be written in any case, in other words, it is case-insensitive. However, the standard practice or the convention is to use uppercase to differentiate it from the arguments. Let's take a relook at the content of Dockerfile in our previous example:
FROM apline:latest CMD echo Hello World!!
Here, FROM is an instruction which has taken apline:latest as an argument, and CMD is an instruction which has taken echo Hello World!! as an argument.