git-mv-after

#! /bin/sh
#
# mv-after: script to rename a file in the index

. git-sh-setup # for die() etc

TAB=$'\t'

# should probably use OPTIONS_SPEC, but not yet
usage()
{
	echo "usage: git mv-after oldname newname"
	echo "${TAB}oldname must exist in the index; newname must not"
}

case $# in
2) ;;
*) usage 1>&2; exit 1;;
esac

# git ls-files --stage does not test whether the entry is actually
# in the index; it exits with status 0 even if not.  But it outputs
# nothing so we can test that.
#
# We do, however, want to make sure that the file is at stage zero
# (only).
getindex()
{
	local output extra

	output="$(git ls-files --stage -- "$1")"
	[ -z "$output" ] && return 1
	extra="$(echo "$output" | sed 1d)"
	[ -z "$extra" ] || return 1
	set -- $output
	[ $3 == 0 ] || return 1
	printf '%s\n' "$output"
}

# check mode of index entry ($1) against arguments $2...$n
# return true if it matches one of them
check_mode()
{
	local i mode=$(echo "$1" | sed 's/ .*//')

	shift
	for i do
		[ "$mode" = "$i" ] && return 0
	done
	return 1
}

# make sure first entry exists
entry="$(getindex "$1")" || die "fatal: cannot find $1"
# make sure second entry does not
getindex "$2" >/dev/null && die "fatal: $2 already in index"

# make sure the mode is 100644 or 100755, it's not clear
# whether this works for anything else and it's clearly
# a bad idea to shuffle a gitlink this way.
check_mode "$entry" 100644 100755 || die "fatal: $1 is not a regular file"

# use git update-index to change the name.  Replace the first
# copy's mode with 0, and the second copy's name with the new name.
# XXX we can't use / as the delimiter in the 2nd sed; use $'\1' as
# an unlikely character
CTLA=$'\1'
printf '%s\n%s\n' "$entry" "$entry" |
    sed -e "1s/100[67][45][45]/000000/" -e "2s$CTLA$TAB.*$CTLA$TAB$2$CTLA" |
    git update-index --index-info