How do I select a merge strategy for a git rebase?

Question

You can use this with Git v1.7.3 or later versions.

git rebase --strategy-option theirs ${branch} # Long option
git rebase -X theirs ${branch} # Short option

(which is a short for git rebase --strategy recursive --strategy-option theirs ${branch} as stated by the documentation)

From Git v1.7.3 Release Notes:

git rebase --strategy <s> learned the --strategy-option/-X option to pass extra options that are understood by the chosen merge strategy.

NB: "Ours" and "theirs" mean the opposite of what they do during a straight merge. In other words, "theirs" favors the commits on the current branch.

This is for merge strategies that come with their own set of options

git rebase <branch> -s recursive -X theirs

should work, although this patch mentions (February 2010):

The manpage says that git-rebase supports merge strategies, but the rebase command doesn't know about -X, and gives the usage when presented with it.

So if it still doesn't work, it is being debated right now!
(supported in recent git)

---

Update from commit db2b3b820e2b28da268cc88adff076b396392dfe (July 2013, git 1.8.4+),

Do not ignore merge options in interactive rebase

Merge strategy and its options can be specified in git rebase, but with -- interactive, they were completely ignored.

Signed-off-by: Arnaud Fontaine

That means -X and strategy now work with interactive rebase, as well as plain rebase.

As iCrazy said, this feature is only available for git 1.7.3 onwards. So, for the poor souls (like me) still using 1.7.1, I present a solution I did myself:

git-rebase-theirs

It is a very well-polished (and thus long) script, meant for production use: ui options, handles multiple files, check if file actually has conflict markers, etc, but the "core" could be summarized in 2 lines:

cp file file.bak
awk '/^<+ HEAD$/,/^=+$/{next} /^>+ /{next} 1' file.bak > file

And here is the full script:

#!/bin/bash
#
# git-rebase-theirs - Resolve rebase conflicts by favoring 'theirs' version
#
#    Copyright (C) 2012 Rodrigo Silva (MestreLion) <[email protected]>
#
#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation, either version 3 of the License, or
#    (at your option) any later version.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License
#    along with this program. If not see <http://www.gnu.org/licenses/gpl.html>

#Defaults:
verbose=0
backup=1
inplace=0
ext=".bak"

message() { printf "%s\n" "$1" >&2 ; }
skip()    { message "skipping ${2:-$file}${1:+: $1}"; continue ; }
argerr()  { printf "%s: %s\n" "$myname" "${1:-error}" >&2 ; usage 1 ; }
invalid() { argerr "invalid option: $1" ; }
missing() { argerr "missing${1:+ $1} operand." ; }

usage() {
    cat <<- USAGE
    Usage: $myname [options] [--] FILE...
    USAGE
    if [[ "$1" ]] ; then
        cat >&2 <<- USAGE
        Try '$myname --help' for more information.
        USAGE
        exit 1
    fi
    cat <<-USAGE

    Resolve git rebase conflicts in FILE(s) by favoring 'theirs' version

    When using git rebase, conflicts are usually wanted to be resolved
    by favoring the <working branch> version (the branch being rebased,
    'theirs' side in a rebase), instead of the <upstream> version (the
    base branch, 'ours' side)

    But git rebase --strategy -X theirs is only available from git 1.7.3
    For older versions, $myname is the solution.

    It works by discarding all lines between '<<<<<<< HEAD' and '========'
    inclusive, and also the the '>>>>>> commit' marker.

    By default it outputs to stdout, but files can be edited in-place
    using --in-place, which, unlike sed, creates a backup by default.

    Options:
      -h|--help            show this page.
      -v|--verbose         print more details in stderr.

      --in-place[=SUFFIX]  edit files in place, creating a backup with
                           SUFFIX extension. Default if blank is ""$ext"

       --no-backup         disables backup

    Copyright (C) 2012 Rodrigo Silva (MestreLion) <[email protected]>
    License: GPLv3 or later. See <http://www.gnu.org/licenses/gpl.html>
    USAGE
    exit 0
}
myname="${0##*/}"

# Option handling
files=()
while (( $# )); do
    case "$1" in
    -h|--help     ) usage            ;;
    -v|--verbose  ) verbose=1        ;;
    --no-backup   ) backup=0         ;;
    --in-place    ) inplace=1        ;;
    --in-place=*  ) inplace=1
                    suffix="${1#*=}" ;;
    -*            ) invalid "$1"     ;;
    --            ) shift ; break    ;;
    *             ) files+=( "$1" )  ;;
    esac
    shift
done
files+=( "$@" )

(( "${#files[@]}" )) || missing "FILE"

ext=${suffix:-$ext}

for file in "${files[@]}"; do

    [[ -f "$file" ]] || skip "not a valid file"

    if ((inplace)); then
        outfile=$(tempfile) || skip "could not create temporary file"
        trap 'rm -f -- "$outfile"' EXIT
        cp "$file" "$outfile" || skip
        exec 3>"$outfile"
    else
        exec 3>&1
    fi

    # Do the magic :)
    awk '/^<+ HEAD$/,/^=+$/{next} /^>+ /{next} 1' "$file" >&3

    exec 3>&-

    ((inplace)) || continue

    diff "$file" "$outfile" >/dev/null && skip "no conflict markers found"

    ((backup)) && { cp "$file" "$file$ext" || skip "could not backup" ; }

    cp "$outfile" "$file" || skip "could not edit in-place"

    ((verbose)) && message "resolved ${file}"
done