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Merge Program
A merge program combines two different versions of a file into a merged file.
Usually, the program tries to do so automatically, by combining all the non-overlapping changes that occurred separately in the two different evolutions of the same initial base file. Furthermore, some interactive merge programs make it easier to manually resolve conflicting merges, either in a graphical way, or by inserting some conflict markers.
By default, Mercurial will attempt to do a classic 3-way merge on text files internally before trying to use an external tool.
Contents
How Mercurial decides which merge program to use
If the HGMERGE environment variable is present, it is used.
Otherwise, if the filename of the file to be merged matches any of the patterns in the merge-patterns configuration section, then the corresponding merge tool is used. (See MergeToolConfiguration for details.)
Otherwise, if the ui.merge config setting is set, that is used. (The next section explains how to configure this.)
Otherwise, if any merge tools are present in the merge-tools configuration section, and any of the tools can be found on the system, the priority settings are used to determine which one to use. (MergeToolConfiguration explains how to configure this.)
Otherwise, if a program named hgmerge exists on the system, that is used.
Otherwise, if the file to be merged is not binary and is not a symlink, then internal:merge is used.
- Otherwise, the merge fails.
However: after selecting a merge program, Mercurial will usually attempt to merge the files using a simple merge algorithm first, to see if they can be merged without conflicts. Only if there are conflicting changes will hg actually execute the merge program. (If the file to be merged is binary or a symlink, then hg doesn't bother with the simple merge algorithm. If the selected merge tool is internal:fail, internal:local, or internal:other, then hg skips the simple merge algorithm, as the user has specifically requested that no merging take place.)
Before Mercurial 1.0, a script named hgmerge was installed by default. As of Mercurial 1.0, hgmerge is no longer installed (and it should not be distributed with Mercurial), but hg still uses it, if it's present on the system and no other merge tools are configured (see hgmerge)
Choosing a merge program
Some merge programs include:
1. Linux merging and diffing tools
KDiff3 - feature-rich merge tool, uses Qt and is thus cross-platform.
Meld - 3-way editor, uses GTK / Gnome and thus Unix only.
gPyFm - merge tool from OpenSolaris, cross-platform.
diff3 - non-interactive merge tool, standard on most Unix/Linux installs. See MergingManuallyInEditor for a wrapper script that uses it with your favorite editor.
tkdiff - known to work under Windows.
DiffMerge - Cross platform feature-rich diffing and merging tool. (free)
"vim -d" - can be used wherever the popular "vim" editor can be found.
Emacs - using either Ediff or Emerge.
P4Merge - Cross platform feature-rich diffing and merging tool. (free)
2. Windows merging and diffing tools
TortoiseMerge - for Windows, part of TortoiseSVN. (open source)
WinMerge - Windows only, as the name suggests. (open source) screenshots
DiffMerge - Cross platform feature-rich diffing and merging tool. (free)
KDiff3 - feature-rich merge tool, uses Qt and is thus cross-platform. (open source)
GnuWin32 - non-interactive merge tool. See MergingManuallyInEditor for a wrapper script that uses it with your favorite editor. (open source)
tkdiff - known to work under Windows. (open source) screenshot
xxdiff - (open source) screenshots
Araxis Merge - A very nice client but expensive (proprietary)
P4Merge - Cross platform feature-rich diffing and merging tool. (free)
Beyond Compare - Extremly good and productive compare tool. (costs some money)
3. OS X merging and diffing tools
FileMerge - Apple's standard gui diffing and merging tool. Part of the standard developer tools (XCode, etc.). (free)
P4Merge - Cross platform feature-rich diffing and merging tool. (free)
DiffMerge - Cross platform feature-rich diffing and merging tool. (free)
Araxis Merge - A very nice very feature rich client but expensive (proprietary)
DeltaWalker - Cross platform fully featured merging and diffing tool (proprietary)
Changes - Native Mac OS X. Mainly for diffing but it can perform simple merges. (proprietary)
BBEdit - Native Mac OS X text editor with diffing and merging capabilities. (proprietary)
TextWrangler - Native Mac OS X text editor with diffing and merging capabilities. (free)
Kaleidoscope - Native Mac OS X gorgeous diffing tool only (proprietary)
DiffFork - Native Mac OS X diffing tool only (also pretty) (proprietary)
KDiff3 - Cross platform and feature-rich, but very un-mac like. (open source)
xxdiff - Cross platform and capable but un-mac like. (open source)
4. Custom merging tools
MergeGettext - A script to merge GNU gettext catalogs
Configuring a merge program
If you have a preferred merge program, you can set the merge entry in the ui section of your hgrc file.
1. Kdiff3
[ui] merge = your-merge-program
In Mercurial 1.0 and later you can also specify the merge program's arguments in .hgrc. For example, to specify the arguments to kdiff3, add the following:
[merge-tools] kdiff3.args = $base $local $other -o $output
(see the external diff extension to configure the diffing aspect of the tool.)
2. Meld
[ui] merge = meld
In Mercurial 1.0 and later you can also specify the merge program's arguments in .hgrc. For example, to specify the arguments to kdiff3, add the following:
[merge-tools] meld.args = $local $base $other $output