Grab All The Method Names Defined In A Ruby File

I wanted a listing of all the methods defined in a Ruby file. Metaprogramming aside, I figured I could write a one-line sed script to effectively do this.

$ sed -n 's/[[:space:]]*def \([[:alnum:]_?!]*\).*/\1/p' file.rb

Let's break this down.

• [[:space:]]* accounts for any level of indentation.

• def matches againts the start of a method definition.

• \(...\) is a capture that can be referenced in the replace side of the script.

• [[:alnum:]_?!]* represents the characters that can make up a Ruby method name, this is equivalent to writing [a-zA-Z0-9_?!]*.

• .* is the final part of the regex match which ensures the rest of the line is loaded into the pattern space so that the replacement will only be the method name.

• \1 replaces everything in the first part of the script with the capture which is just the method name.

• combining the -n and p flags ensures that only lines with substitutions are printed.

This probably isn't perfect, but it is good enough to reference from time to time in my shell history.