sample m4 macro to check library

check_library.m4

# libsnappy_tests.m4

# gl_LIBSNAPPY_TESTS()
# -------------------
# Check if libsnappy is available.
AC_DEFUN([gl_LIBSNAPPY_TESTS],
[
  LIBSNAPPY_LIBS=
  LIBSNAPPY_LDFLAGS=
  LDFLAGS_SAVE="$LDFLAGS"
  if test -n "$LIBSNAPPY_SEARCH_LIBS"; then
    LDFLAGS="-L$LIBSNAPPY_SEARCH_LIBS $LDFLAGS"
    AC_CHECK_LIB(snappy, snappy_compress,
      [
        LIBSNAPPY_LDFLAGS="-L$LIBSNAPPY_SEARCH_LIBS"
        LIBSNAPPY_LIBS="-lsnappy"
      ],
      [
        AC_MSG_ERROR([required library libsnappy was not found in requested location $LIBSNAPPY_SEARCH_LIBS])
      ]
    )
  else
    AC_CHECK_LIB(snappy, snappy_compress,
      [],
      [
        AC_MSG_ERROR([required library libsnappy was not found on your system, please check https://code.google.com/p/snappy/])
      ]
    )
  fi
  LDFLAGS="$LDFLAGS_SAVE"
  AC_SUBST(LIBSNAPPY_LIBS)
  AC_SUBST(LIBSNAPPY_LDFLAGS)
])