Create repo-tool.md

Author: narendasan

_til/git/repo-tool.md

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+---
+title: Repo Tool
+category: git
+---
+
+When getting into more complicated software development, you will usually end
+up having code split in mulitple repos. Groot, Merch and the GPU Cluster
+are all examples of moduluar projects with multiple repos. 
+
+There are a couple ways to manage all the repos you use. Git submodules are one
+and they are really good for vendoring code that you don't actively develop in 
+parallel with the code you are working on. It works by checking out a specific 
+commit from another repo.
+
+Another tool more suited to parallel development is ```repo```. It is a tool
+created by Google for use on Android, to manage the various repos the project has.
+
+Many ACM projects also use ```repo`` to manage their sub repos. 
+
+## Installing ```Repo```
+
+Installing repo is easy, many OSes have it included in their package manager
+
+```sh
+brew install repo 
+```
+
+```sh
+apt install repo
+```
+
+## Managing Repos
+
+Managing repos is done through a manifest in the format of an xml file. 
+Within the xml file, the root git server is listed and the subdirectories 
+of the repos are listed with their final arrangement on the client. 
+
+```xml
+<?xml version="1.0" encoding="UTF-8"?>
+<manifest>
+  <!-- Location of the git server (notice the protocol definition) --> 
+	<remote name="origin" fetch="ssh://git@github.com/acm-uiuc/"  />
+
+  <!-- Default name for remote and branch --> 
+	<default remote="origin" revision="master" />
+  
+  <!-- Path to place each repo on client and the name of the subdirectory on the git server for each repo --> 
+	<project path="." name="merch" />
+	<project path="merch-embedded" name="merch-embedded" />
+	<project path="merch-hardware" name="merch-hardware" />
+	<project path="merch-ios" name="merch-ios" />
+
+</manifest>
+
+```
+
+Call this file ```default.xml``` and place it at the root of your main repo
+
+> Note: It is recommended to use ssh with repo since you then don't need to use a password for every ``clone/push/pull```
+
+## Getting All Your Code
+
+To begin with, ```repo``` needs a directory to work in. So create one 
+
+```sh
+mkdir merch 
+```
+
+Then you must initialize ```repo``` in that directory 
+
+```sh
+repo init -u git@github.com:acm-uiuc/merch
+```
+
+Finally pull the latest changes 
+
+```sh
+repo sync 
+```
+
+You should now have all your code placed in the right places to start working 
+
+To commit code back up use the standard ```git``` workflow 
+
+## Cool Abilities 
+
+Repo also allows you to do some powerful things
+
+For instance 
+
+```sh
+repo forall 
+
+```
+Runs a command in every repo, good for pushing up a bunch of changes.
+
+For the full reference checkout https://source.android.com/source/using-repo