=head1 NAME

docs/project/git_terminology.pod - Git Terminology

=head1 DESCRIPTION

This document describes terms that are used in F<docs/project/git_workflow.pod>
and contains generally useful things to know about Git.

=head1 INTRODUCTION

Before learning any terminology, there are a few very basic things that
should be understood about Git, which will provide a foundation for
understanding anything else.

A Git repository is a Directed Acyclic Graph (DAG), where each node in the
graph is a commit, with zero or more parents. A root commit of a
repository has zero parents, others have at least one parent. A repository
may have any number of root commits, but many have only one. If a commit has
more than one parent, that means it was the result of a merge.

Each commit is uniquely identified by a SHA1 sum. You may refer to any commit
by the first few characters of a SHA1 sum, as long as it is unique. If it is
not unique, C<git> will complain loudly. Usually 6-7 characters of a SHA1 is
sufficient, but this number increases as the number of commits in a repo
grows.

There are three distinct "places" in a Git repository, which are referred to
as the index, the working copy, and the staging area. The index is the actual
DAG, where all the history of the repo is stored. This lives in the .git
directory of a repository. The "working copy" are the actual files on the
filesystem. The staging area is where things that will be included in the
next commit live, which happens to be inside the .git directory as well.
When you type C<git add foo>, you are adding the file/directory foo to the
staging area. When you type C<git log> you are asking the index to show
you a log of all commits. When you run a non-git command in a repo, such
as C<rm foo>, you are modifying the working copy.

The most important thing to learn when understanding a C<git> command is whether
it operates on the index, working copy, staging area or a combination of the
three. Also note that certain C<git> commands can operate on different areas
when given different command-line options.

=head1 HELPING YOURSELF

Git comes with extensive documentation. To get the short help summary for a git
command, do C<git cmd -h>. To see the manual for a git command, type C<git help
cmd>, where "cmd" is the name of the command you want to look up.

=head1 TERMS

=head2 branch

Noun. A symbolic name referring to a commit SHA1. The master branch is just a branch
called master, it is not special in any way except that it is the default.

Verb. To create a divergent history of commits from a given commit, branch or tag.

=head2 clone

Verb. The term used for copying a remote repo locally, which contains the entire
history of the git repo being cloned.

=head2 commit-ish, committish

Noun. A general term for a way to describe a set of commits.

=head2 rebase

Verb. Update the local index with changes from a remote, then replay local changes,
in order, on top of them. This prevents "useless merge commits", such as:

    Merge branch 'master' of github.com:parrot/parrot

The C<git pull --rebase> command can be used to update your master branch from
the remote called 'origin'. There is also a C<git rebase> command that can be
used to rebase branches onto each other.

=head2 remote

Noun. A remote is basically a URL with metadata that describes where changes are
pushed/pulled from.  A git repo may have any number of remotes. The default
remote is where the repo was originally cloned from and it has the name
"origin".

=head2 repo

Noun. Short for repository.

=head2 SHA1

Noun. Secure Hash Algorithm 1. Also called a SHA1 sum or SHA1 hash. Every git commit
is uniquely identified by a SHA1. This is roughly similar to a Subversion
Revision, but it is not an integer and does not increase linearly, because git
commits can have any number of parents.

=head2 tag

Noun. A symbolic name for a SHA1. A tag is like a variable, which points to a specific SHA1.
Tags can change, but usually they don't. A tag is akin to a domain name, which points to
an IP address. Run C<git help tag> for more information.

Verb. The process of giving a sha1 a symbolic name, such as giving commit 9560334cf the symbolic
name "RELEASE_42_0_1".

=head2 topic branch

Noun. Any branch that is not the master branch.

=head1 SEE ALSO

F<docs/project/git_workflow.pod>

=cut

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