Working directory
The working directory is the top-level directory in a [:Repository:repository], in which the plain versions of files are available to read, edit and build. Files in the working directory are usually from the [:Tip:tip], but may be from older [:Revision:revisions], or modified and not yet [:Commit:committed].
It’s useful to think of the working directory as "the changeset I’m about to commit". If the working directory has no [:LocalModifications:local modifications] it is said to be clean.
Use hg revert to discard all local modifications (see [:Revert]).
Use hg update to bring the working directory into sync with a particular [:ChangeSet:changeset] (see [:Update]).
To remove all files from the working directory (not the repository!), you can do
hg update null
A [:NamedBranches:branch name] can be set for the working directory.
Mercurial tracks various information about the working directory (see DirState).
1. Parent(s)
A working directory has one or two [:Parent:parent] revisions. The parent revision (or revisions) will become the parent revisions of the new revision which will eventually be created by a commit of the local modifications.
An hg update will change the parent revision, whereas hg revert will only modify the content of the working directory.
A working directory will only have two parent revisions as the result of a [:Merge:merge].
2. When an update is needed
There are several ways to see if an update of your working directory is needed (see related [http://www.selenic.com/pipermail/mercurial/2006-September/010951.html mailing list thread]):
To see the delta between the working directory and the tip, do:
hg diff -r tip
To see what patches would be applied to the working directory on an update do:
hg log -r tip:.
If the working directory is at the tip (that is, no update needed)
hg id
will write "tip" after the changeset id.