This is an introduction to how to write programs in Stata. To try this out yourself, download this Gist by clicking Download Zip. Unpack the .zip file and edit the path global in the runfile.do. Then follow these instructions and run the corresponding section of the run file.
If you have any questions or want us to add another examples on how you can expand myhist.ado as us in the comment section below.
It is common in computer science that the first function/command you write is a simple command that just display the message Hello World!. That is what the program in hello_world.ado does.
Here we are set-by-step writing a command that takes a variable and creates a histogram with that variable. In a real life scenario this command could be expanded so that the command includes a lot of histogram options so that you can easily apply them to many histograms by typing myhist varA, myhist varB, myhist varC etc.
This is the simplest possible version of this command. The syntax takes exactly one variable (because we use varname instead of varlist) and create a histogram of the distribution in that variable.
In this version we have added one option called title() that takes a string. We add "DIME -" in front of that string and then use it as the title of the historgram.
What you call your options does not matter at all to Stata. myhist_v3.ado gives the exact same result as myhist_v2.ado, but the title() option is called xyz(). You should always chose a name that make sense to humans as it will make it easier for humans to read the code - so xyz is a terrible name - but it makes no difference to Stata.