/usr/bin/wmanager-loop is in wmanager 0.2.1-11.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 | #!/bin/sh -e
#  wmanager-loop -- loop running window managers chosen with wmanager
#  Copyright (C) 2000  Tommi Virtanen <tv@debian.org>
#  Copyright (C) 2008, 2009  Peter Pentchev <roam@ringlet.net>
#  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 2 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, write to the Free Software
#  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
# Search .wmanagerrc for the WM specified by the user
check_wm()
{
	local wm esc try
	# A directly specified executable file
	if [ -x "$1" ]; then
		echo "$1"
		return 0
	fi
	# No, we'll have to look through .wmanagerrc
	if [ ! -r "$RC" ]; then
		echo "Nonexistent or unreadable config file: $RC" 1>&2
		return 1
	fi
	if `expr "$1" : '.*[^A-Za-z0-9_/-]' > /dev/null`; then
		echo "Invalid characters in WM specification: $1" 1>&2
		return 1
	fi
	wm="$1"
	esc=`echo "$1" | sed -e 's@/@\\\\/@g'`
	# An exact match
	try=`awk -F= '$1 == "'$wm'" {print $2}' "$RC"`
	if [ -n "$try" ]; then
		echo "$try"
		return 0
	fi
	# An exact match for the program
	try=`awk -F= '$2 ~ /\/'"$esc"'$/ {print $2}' "$RC"`
	if [ -n "$try" ]; then
		set $try
		if [ "$#" -gt 1 ]; then
			echo "Ambiguous WM specification '$wm': $@" 1>&2
			return 1
		fi
		echo "$try"
		return 0
	fi
	# A WM starting with the specified string
	try=`awk -F= '$2 ~ /\/'"$esc"'[^\/]*$/ {print $2}' "$RC"`
	if [ -n "$try" ]; then
		set $try
		if [ "$#" -gt 1 ]; then
			echo "Ambiguous WM specification '$wm': $@" 1>&2
			return 1
		fi
		echo "$try"
		return 0
	fi
	# A WM ending with the specified string
	try=`awk -F= '$2 ~ /'"$esc"'$/ {print $2}' "$RC"`
	if [ -n "$try" ]; then
		set $try
		if [ "$#" -gt 1 ]; then
			echo "Ambiguous WM specification '$wm': $@" 1>&2
			return 1
		fi
		echo "$try"
		return 0
	fi
	echo "Invalid WM specification '$wm'" 1>&2
	return 1
}
RC="$HOME/.wmanagerrc"
if [ -n "$WM" ]; then
	WM=`check_wm "$WM"`
	[ -n "$WM" ] || exit 1
fi
if [ -z "$WM" ] && [ -r "$RC" ]; then
	WM="$(sed 's/^.*=//; q' "$RC")"
fi
if [ -z "$WMTERM" ]; then
	WMTERM='xterm'
	for prog in x-terminal-emulator urxvt rxvt xterm; do
		WMCMD=`which "$prog" || true`
		if [ -n "$WMCMD" ]; then
			WMTERM="$WMCMD"
			break
		fi
	done
fi
while [ "$WM" != "-1" ]; do
    ${WM:-"$WMTERM"} || true
    WM="$(wmanager "$@" || true)"
done
 |