gosed

Go Stream Editor

A Go CLI program that reads go source code, manipulate the code and then writes it back.

Motivation

Go generics discussions has been going on for a while in the Go community. but the simplicity of the language allows for writing generators to achieve the same result.

The idea is writing valid Go code with tests and benchmarks and everything. then use go:generate to run a tool like gosed that reads this code, parse it, perform some operations on it like replacing types, functions names, package name...etc then write it out to another go file.

So gosed is one tool that can do that. it's a command line program that can read one or multiple files, perform one or more processing steps and then write it to one or more destinations.

How it works

gosed works with steps, the command line arguments takes the general form:

gosed [--step-name [--step-arg1=step-arg1-value...]]...

• So a step name can be input to read from a file write to write to a file, rename-package to change package name.
• input step for example takes one argument which is path a path to the file to read.

Example

To read a file, change the package name and write it back to another file

gosed
  --input --path=main.go \
  --rename-package --to=mypackage \
  --write --path=mypackage.go

This reads file main.go, rename the package to mypackage then writes it to mypackage.go file.

Installation

go install github.com/emad-elsaid/gosed@latest

Steps

gosed has a set of step, which is the mutations that can be done to a stream of go code.

input

• Name: input
• Arguments:
  • path: the path to the file to read
• Description: reads a file and append it to the stream of inputs, so using it multiple times will concatenate multiple files and process them as one stream.

write

• Name: write
• Arguments:
  • path: the path to a file to write output
• Description: writes the output of the last step to a file specified in path. doesn't create the directories to this file.

rename-package

• Name: rename-package
• Arguments:
  • to: the name of the new package
• Description: find the package declarations in the stream and rename it to to argument value

Contribution

• The whole program is one main package
• Every step is a file in the form step-name.go
• The file should define a function of type editor
• The step should be added to the main.go file with the required arguments
• The editor function is a sort of a pipe, takes the code as bytes, manipulate it as you wish and return the new version and error.
• The main function will use the steps and if one of the steps returned an error it'll print the error and exit.