如何从bazel中的文件导出环境变量

def _export_env_var_impl(ctx):
    var_value = ctx.attr.value
    output_file = ctx.outputs.out

    ctx.actions.write(output_file, var_value)

export_env_var = rule(
    implementation = _export_env_var_impl,
    attrs = {
        "value": attr.string(default=""),
        "out": attr.output(),
    },
)

load("//path/to/export_env_var.bzl", "export_env_var")

export_env_var(
    name = "export_my_var",
    value = "my_value",
    out = "env_var.txt",
)

bazel build //path/to:export_my_var