m4/st_save_restore_var.m4 - platform/external/strace - Git at Google

 AC_DEFUN([st_SAVE_VAR], [dnl
 AS_IF([test -n "${$1+set}"], [st_saved_$1="${$1}"; unset $1])
 ])

 AC_DEFUN([st_RESTORE_VAR], [dnl
 AS_IF([test -n "${st_saved_$1+set}"], [$1="${st_saved_$1}"; unset st_saved_$1])
 ])
	AC_DEFUN([st_SAVE_VAR], [dnl
	AS_IF([test -n "${$1+set}"], [st_saved_$1="${$1}"; unset $1])
	])

	AC_DEFUN([st_RESTORE_VAR], [dnl
	AS_IF([test -n "${st_saved_$1+set}"], [$1="${st_saved_$1}"; unset st_saved_$1])
	])