Mercurial: The Definitive Guide

Making and Reviewing Changes

Now that we have a grasp of viewing history in Mercurial, let’s take a look at making some changes and examining them.

The first thing we’ll do is isolate our experiment in a repository of its own. We use the hg clone command, but we don’t need to clone a copy of the remote repository. Since we already have a copy of it locally, we can just clone that instead. This is much faster than cloning over the network, and cloning a local repository uses less disk space in most cases, too.^[1]

$ cd ..
$ hg clone hello my-hello
updating working directory
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$cd my-hello

As an aside, it’s often good practice to keep a “pristine” copy of a remote repository around, which you can then make temporary clones of to create sandboxes for each task you want to work on. This lets you work on multiple tasks in parallel, each isolated from the others until it’s complete and you’re ready to integrate it back. Because local clones are so cheap, there’s almost no overhead to cloning and destroying repositories whenever you want.

In our my-hello repository, we have a file hello.c that contains the classic “hello, world” program.

$ cat hello.c
/*
 * Placed in the public domain by Bryan O'Sullivan.  This program is
 * not covered by patents in the United States or other countries.
 */

#include <stdio.h>

int main(int argc, char **argv)
{
	printf("hello, world!\");
	return 0;
}

Let’s edit this file so that it prints a second line ...