proc {file copy} {{force {}} source target} {
	try {
		if {$force ni {{} -force}} {
			error "bad option \"$force\": should be -force"
		}

		if {![file exists $source]} {
			error "source file does not exist."
		}

		if {$force eq "" && [file exists $target]} {
			error "error copying \"$source\" to \"$target\": file already exists"
		}
		exec /mod/bin/busybox/cp $source $target
	} on error {msg opts} {
		incr opts(-level)
		return {*}$opts $msg
	}
}