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// [**libgit2**][lg] is a portable, pure C implementation of the Git core methods
// provided as a re-entrant linkable library with a solid API, allowing you
// to write native speed custom Git applications in any language which
// supports C bindings.
// [This file][ex] is an example of using that API in a real, compilable C file.
// Before published, this file is compiled and run to make sure it actually
// runs. As the API is updated, this file will be updated to demonstrate the
// new functionality. This project is [on GitHub][ex].
// If you're trying to write something in C using [libgit2][lg], you will also want
// to check out the generated [API documentation][ap] and the [Usage Guide][ug]. We've
// tried to link to the relevant sections of the API docs in each section in this file.
// **libgit2** only implements the core plumbing functions, not really the higher
// level porcelain stuff. For a primer on Git Internals that you will need to know
// to work with Git at this level, check out [Chapter 9][pg] of the Pro Git book.
// [lg]:
// [ap]:
// [ug]:
// [pg]:
// [ex]:
// ### Includes
// Including the `git2.h` header will include all the other libgit2 headers that you need.
// It should be the only thing you need to include in order to compile properly and get
// all the libgit2 API.
#include <git2.h>
#include <stdio.h>
int main (int argc, char** argv)
// ### Opening the Repository
// There are a couple of methods for opening a repository, this being the simplest.
// There are also [methods][me] for specifying the index file and work tree locations, here
// we are assuming they are in the normal places.
// [me]:
git_repository *repo;
git_repository_open(&repo, "/opt/libgit2-test/.git");
// ### SHA-1 Value Conversions
// For our first example, we will convert a 40 character hex value to the 20 byte raw SHA1 value.
printf("*Hex to Raw*\n");
char hex[] = "fd6e612585290339ea8bf39c692a7ff6a29cb7c3";
// The `git_oid` is the structure that keeps the SHA value. We will use this throughout the example
// for storing the value of the current SHA key we're working with.
git_oid oid;
git_oid_mkstr(&oid, hex);
// Once we've converted the string into the oid value, we can get the raw value of the SHA.
printf("Raw 20 bytes: [%s]\n", (&oid)->id);
// Next we will convert the 20 byte raw SHA1 value to a human readable 40 char hex value.
printf("\n*Raw to Hex*\n");
char out[41];
out[40] = '\0';
// If you have a oid, you can easily get the hex value of the SHA as well.
git_oid_fmt(out, &oid);
printf("SHA hex string: %s\n", out);
// ### Working with the Object Database
// **libgit2** provides [direct access][odb] to the object database.
// The object database is where the actual objects are stored in Git. For
// working with raw objects, we'll need to get this structure from the
// repository.
// [odb]:
git_odb *odb;
odb = git_repository_database(repo);
// #### Raw Object Reading
printf("\n*Raw Object Read*\n");
git_odb_object *obj;
git_otype otype;
const unsigned char *data;
const char *str_type;
int error;
// We can read raw objects directly from the object database if we have the oid (SHA)
// of the object. This allows us to access objects without knowing thier type and inspect
// the raw bytes unparsed.
error = git_odb_read(&obj, odb, &oid);
// A raw object only has three properties - the type (commit, blob, tree or tag), the size
// of the raw data and the raw, unparsed data itself. For a commit or tag, that raw data
// is human readable plain ASCII text. For a blob it is just file contents, so it could be
// text or binary data. For a tree it is a special binary format, so it's unlikely to be
// hugely helpful as a raw object.
data = (const unsigned char *)git_odb_object_data(obj);
otype = git_odb_object_type(obj);
// We provide methods to convert from the object type which is an enum, to a string
// representation of that value (and vice-versa).
str_type = git_object_type2string(otype);
printf("object length and type: %d, %s\n",
// For proper memory management, close the object when you are done with it or it will leak
// memory.
// #### Raw Object Writing
printf("\n*Raw Object Write*\n");
// You can also write raw object data to Git. This is pretty cool because it gives you
// direct access to the key/value properties of Git. Here we'll write a new blob object
// that just contains a simple string. Notice that we have to specify the object type as
// the `git_otype` enum.
git_odb_write(&oid, odb, "test data", sizeof("test data") - 1, GIT_OBJ_BLOB);
// Now that we've written the object, we can check out what SHA1 was generated when the
// object was written to our database.
git_oid_fmt(out, &oid);
printf("Written Object: %s\n", out);
// ### Object Parsing
// libgit2 has methods to parse every object type in Git so you don't have to work directly
// with the raw data. This is much faster and simpler than trying to deal with the raw data
// yourself.
// #### Commit Parsing
// [Parsing commit objects][pco] is simple and gives you access to all the data in the commit
// - the // author (name, email, datetime), committer (same), tree, message, encoding and parent(s).
// [pco]:
printf("\n*Commit Parsing*\n");
git_commit *commit;
git_oid_mkstr(&oid, "f0877d0b841d75172ec404fc9370173dfffc20d1");
error = git_commit_lookup(&commit, repo, &oid);
const git_signature *author, *cmtter;
const char *message, *message_short;
time_t ctime;
unsigned int parents, p;
// Each of the properties of the commit object are accessible via methods, including commonly
// needed variations, such as `git_commit_time` which returns the author time and `_message_short`
// which gives you just the first line of the commit message.
message = git_commit_message(commit);
message_short = git_commit_message_short(commit);
author = git_commit_author(commit);
cmtter = git_commit_committer(commit);
ctime = git_commit_time(commit);
// The author and committer methods return [git_signature] structures, which give you name, email
// and `when`, which is a `git_time` structure, giving you a timestamp and timezone offset.
printf("Author: %s (%s)\n", author->name, author->email);
// Commits can have zero or more parents. The first (root) commit will have no parents, most commits
// will have one, which is the commit it was based on, and merge commits will have two or more.
// Commits can technically have any number, though it's pretty rare to have more than two.
parents = git_commit_parentcount(commit);
for (p = 0;p < parents;p++) {
git_commit *parent;
git_commit_parent(&parent, commit, p);
git_oid_fmt(out, git_commit_id(parent));
printf("Parent: %s\n", out);
// Don't forget to close the object to prevent memory leaks. You will have to do this for
// all the objects you open and parse.
// #### Writing Commits
// libgit2 provides a couple of methods to create commit objects easily as well. There are four
// different create signatures, we'll just show one of them here. You can read about the other
// ones in the [commit API docs][cd].
// [cd]:
printf("\n*Commit Writing*\n");
git_oid tree_id, parent_id, commit_id;
// Creating signatures for an authoring identity and time is pretty simple - you will need to have
// this to create a commit in order to specify who created it and when. Default values for the name
// and email should be found in the `` and `` configuration options. See the `config`
// section of this example file to see how to access config values.
author = git_signature_new("Scott Chacon", "",
123456789, 60);
cmtter = git_signature_new("Scott A Chacon", "",
987654321, 90);
// Commit objects need a tree to point to and optionally one or more parents. Here we're creating oid
// objects to create the commit with, but you can also use
git_oid_mkstr(&tree_id, "28873d96b4e8f4e33ea30f4c682fd325f7ba56ac");
git_oid_mkstr(&parent_id, "f0877d0b841d75172ec404fc9370173dfffc20d1");
// Here we actually create the commit object with a single call with all the values we need to create
// the commit. The SHA key is written to the `commit_id` variable here.
&commit_id, /* out id */
NULL, /* do not update the HEAD */
"example commit",
1, &parent_id);
// Now we can take a look at the commit SHA we've generated.
git_oid_fmt(out, &commit_id);
printf("New Commit: %s\n", out);
// #### Tag Parsing
// You can parse and create tags with the [tag management API][tm], which functions very similarly
// to the commit lookup, parsing and creation methods, since the objects themselves are very similar.
// [tm]:
printf("\n*Tag Parsing*\n");
git_tag *tag;
const char *tmessage, *tname;
git_otype ttype;
// We create an oid for the tag object if we know the SHA and look it up in the repository the same
// way that we would a commit (or any other) object.
git_oid_mkstr(&oid, "bc422d45275aca289c51d79830b45cecebff7c3a");
error = git_tag_lookup(&tag, repo, &oid);
// Now that we have the tag object, we can extract the information it generally contains: the target
// (usually a commit object), the type of the target object (usually 'commit'), the name ('v1.0'),
// the tagger (a git_signature - name, email, timestamp), and the tag message.
git_tag_target((git_object **)&commit, tag);
tname = git_tag_name(tag); // "test"
ttype = git_tag_type(tag); // GIT_OBJ_COMMIT (otype enum)
tmessage = git_tag_message(tag); // "tag message\n"
printf("Tag Message: %s\n", tmessage);
// #### Tree Parsing
// [Tree parsing][tp] is a bit different than the other objects, in that we have a subtype which is the
// tree entry. This is not an actual object type in Git, but a useful structure for parsing and
// traversing tree entries.
// [tp]:
printf("\n*Tree Parsing*\n");
git_tree *tree;
git_tree_entry *entry;
git_object *objt;
// Create the oid and lookup the tree object just like the other objects.
git_oid_mkstr(&oid, "2a741c18ac5ff082a7caaec6e74db3075a1906b5");
git_tree_lookup(&tree, repo, &oid);
// Getting the count of entries in the tree so you can iterate over them if you want to.
int cnt = git_tree_entrycount(tree); // 3
printf("tree entries: %d\n", cnt);
entry = git_tree_entry_byindex(tree, 0);
printf("Entry name: %s\n", git_tree_entry_name(entry)); // "hello.c"
// You can also access tree entries by name if you know the name of the entry you're looking for.
entry = git_tree_entry_byname(tree, "hello.c");
git_tree_entry_name(entry); // "hello.c"
// Once you have the entry object, you can access the content or subtree (or commit, in the case
// of submodules) that it points to. You can also get the mode if you want.
git_tree_entry_2object(&objt, repo, entry); // blob
// Remember to close the looked-up object once you are done using it
// #### Blob Parsing
// The last object type is the simplest and requires the least parsing help. Blobs are just file
// contents and can contain anything, there is no structure to it. The main advantage to using the
// [simple blob api][ba] is that when you're creating blobs you don't have to calculate the size
// of the content. There is also a helper for reading a file from disk and writing it to the db and
// getting the oid back so you don't have to do all those steps yourself.
// [ba]:
printf("\n*Blob Parsing*\n");
git_blob *blob;
git_oid_mkstr(&oid, "af7574ea73f7b166f869ef1a39be126d9a186ae0");
git_blob_lookup(&blob, repo, &oid);
// You can access a buffer with the raw contents of the blob directly.
// Note that this buffer may not be contain ASCII data for certain blobs (e.g. binary files):
// do not consider the buffer a NULL-terminated string, and use the `git_blob_rawsize` attribute to
// find out its exact size in bytes
printf("Blob Size: %d\n", git_blob_rawsize(blob)); // 8
git_blob_rawcontent(blob); // "content"
// ### Revwalking
// The libgit2 [revision walking api][rw] provides methods to traverse the directed graph created
// by the parent pointers of the commit objects. Since all commits point back to the commit that
// came directly before them, you can walk this parentage as a graph and find all the commits that
// were ancestors of (reachable from) a given starting point. This can allow you to create `git log`
// type functionality.
// [rw]:
git_revwalk *walk;
git_commit *wcommit;
git_oid_mkstr(&oid, "f0877d0b841d75172ec404fc9370173dfffc20d1");
// To use the revwalker, create a new walker, tell it how you want to sort the output and then push
// one or more starting points onto the walker. If you want to emulate the output of `git log` you
// would push the SHA of the commit that HEAD points to into the walker and then start traversing them.
// You can also 'hide' commits that you want to stop at or not see any of their ancestors. So if you
// want to emulate `git log branch1..branch2`, you would push the oid of `branch2` and hide the oid
// of `branch1`.
git_revwalk_new(&walk, repo);
git_revwalk_sorting(walk, GIT_SORT_TOPOLOGICAL | GIT_SORT_REVERSE);
git_revwalk_push(walk, &oid);
const git_signature *cauth;
const char *cmsg;
// Now that we have the starting point pushed onto the walker, we can start asking for ancestors. It
// will return them in the sorting order we asked for as commit oids.
// We can then lookup and parse the commited pointed at by the returned OID;
// note that this operation is specially fast since the raw contents of the commit object will
// be cached in memory
while ((git_revwalk_next(&oid, walk)) == GIT_SUCCESS) {
error = git_commit_lookup(&wcommit, repo, &oid);
cmsg = git_commit_message_short(wcommit);
cauth = git_commit_author(wcommit);
printf("%s (%s)\n", cmsg, cauth->email);
// Like the other objects, be sure to free the revwalker when you're done to prevent memory leaks.
// Also, make sure that the repository being walked it not deallocated while the walk is in
// progress, or it will result in undefined behavior
// ### Index File Manipulation
// The [index file API][gi] allows you to read, traverse, update and write the Git index file
// (sometimes thought of as the staging area).
// [gi]:
printf("\n*Index Walking*\n");
git_index *index;
unsigned int i, e, ecount;
// You can either open the index from the standard location in an open repository, as we're doing
// here, or you can open and manipulate any index file with `git_index_open_bare()`. The index
// for the repository will be located and loaded from disk.
git_index_open_inrepo(&index, repo);
// For each entry in the index, you can get a bunch of information including the SHA (oid), path
// and mode which map to the tree objects that are written out. It also has filesystem properties
// to help determine what to inspect for changes (ctime, mtime, dev, ino, uid, gid, file_size and flags)
// All these properties are exported publicly in the `git_index_entry` struct
ecount = git_index_entrycount(index);
for (i = 0; i < ecount; ++i) {
git_index_entry *e = git_index_get(index, i);
printf("path: %s\n", e->path);
printf("mtime: %d\n", (int)e->mtime.seconds);
printf("fs: %d\n", (int)e->file_size);
// ### References
// The [reference API][ref] allows you to list, resolve, create and update references such as
// branches, tags and remote references (everything in the .git/refs directory).
// [ref]:
printf("\n*Reference Listing*\n");
// Here we will implement something like `git for-each-ref` simply listing out all available
// references and the object SHA they resolve to.
git_strarray ref_list;
git_reference_listall(&ref_list, repo, GIT_REF_LISTALL);
const char *refname, *reftarget;
git_reference *ref;
// Now that we have the list of reference names, we can lookup each ref one at a time and
// resolve them to the SHA, then print both values out.
for (i = 0; i < ref_list.count; ++i) {
refname = ref_list.strings[i];
git_reference_lookup(&ref, repo, refname);
switch (git_reference_type(ref)) {
git_oid_fmt(out, git_reference_oid(ref));
printf("%s [%s]\n", refname, out);
printf("%s => %s\n", refname, git_reference_target(ref));
// Finally, when you're done with the repository, you can free it as well.