Cowsay.jl/docs/src/cowfiles.md

Making a cow function

The original cowsay used Perl scripts (called 'cowfiles') to allow for creating more ASCII cow art. Cowsay.jl uses Julia functions, instead. In order to be usable by Cowsay.cowsay, a cow function must

1. Take the correct arguments

   The function must take three (3) keyword arguments of the form

   • eyes::AbstractString="oo"
   • tongue::AbstractString=" "
   • thoughts::AbstractString="\\"

   When drawing the cow artwork, you may then use the variables eyes in place of the eyes, tongue in place of the tongue, and thoughts in place of the speech ballon trail. Use of these variables in constructing the cow is optional (but makes the use of your cow function far more fun), but all three arguments must be present in the signature, regardless.

2. Return a string

   The cow artwork must be returned from the function as a string. This is distinctly different from how the original cowsay modified the $the_cow variable.

Helpful hints for making cow functions

1. Include one function per file, with the extension .cow.jl
2. Do not indent within a .cow.jl file to better see the artwork
3. Make use of string literals (""") and string interpolation ($) to build the cow art
4. Be sure to escape backslashes (\) and dollar signs ($) within your artwork
5. When converting from Perl cowfiles, unescape at symbols (@), as these are not special in Julia strings
6. Split the eyes variable to get individual left- and right-eye when creating large cow functions
7. Have fun!