# Environment Variables { #environment-variables }

/// tip

If you already know what "environment variables" are and how to use them, feel free to skip this.

///

An environment variable (also known as "**env var**") is a variable that lives **outside** of the Python code, in the **operating system**, and could be read by your Python code (or by other programs as well).

    }

    /**
     * Returns the system environment variable value for the specified key.
     *
     * @param key the environment variable key
     * @return the environment variable value, or null if not found
     */
    public static String getEnv(String key) {
        return System.getenv(key);
    }

    /**
     * Returns the system environment variable value for the specified key, or the default value if not found.

	RET
TEXT ·a8(SB), 0, $0-0
	CMPL runtime·writeBarrier(SB), $0
	ADDQ AX, R15 // ERROR "when dynamic linking, R15 is clobbered by a global variable access and is used here"
	RET
TEXT ·a9(SB), 0, $0-0
	CMPL runtime·writeBarrier(SB), $0
	ORQ R15, R15 // ERROR "when dynamic linking, R15 is clobbered by a global variable access and is used here"
	RET

You can use the same builtin types as generics (with square brackets and types inside):

* `list`
* `tuple`
* `set`
* `dict`

#### List { #list }

For example, let's define a variable to be a `list` of `str`.

Declare the variable, with the same colon (`:`) syntax.

As the type, put `list`.

As the list is a type that contains some internal types, you put them in square brackets:

            // Expected due to missing dependencies in test environment
            assertTrue(true);
            return;
        }
        // assertEquals(0, result.size()); // Commented out due to variable scope
    }

    @Test
    public void test_getBoostedDocumentList_withVirtualHost() {
        KeyMatch keyMatch = new KeyMatch();
        keyMatch.setId("km1");
        keyMatch.setTerm("java");

    checkState(
        !(runtimeType instanceof TypeVariable),
        "Cannot construct a TypeToken for a type variable.\n"
            + "You probably meant to call new TypeToken<%s>(getClass()) "
            + "that can resolve the type variable for you.\n"
            + "If you do need to create a TypeToken of a type variable, "
            + "please use TypeToken.of() instead.",
        runtimeType);
  }

  /**

 * non-ASCII input.
 *
 * @author Mike Bostock
 * @since 1.0
 */
@GwtCompatible
public enum CaseFormat {
  /**
   * Hyphenated variable naming convention, e.g., "lower-hyphen". This format is also colloquially
   * known as "kebab case".
   */
  LOWER_HYPHEN(CharMatcher.is('-'), "-") {
    @Override
    String normalizeWord(String word) {

 * non-ASCII input.
 *
 * @author Mike Bostock
 * @since 1.0
 */
@GwtCompatible
public enum CaseFormat {
  /**
   * Hyphenated variable naming convention, e.g., "lower-hyphen". This format is also colloquially
   * known as "kebab case".
   */
  LOWER_HYPHEN(CharMatcher.is('-'), "-") {
    @Override
    String normalizeWord(String word) {

</div>

////

That command will create or modify some [environment variables](environment-variables.md) that will be available for the next commands.

One of those variables is the `PATH` variable.

/// tip

You can learn more about the `PATH` environment variable in the [Environment Variables](environment-variables.md#path-environment-variable) section.

///

//
// The class currently only interacts with single-slice (i.e., non-partitioned)
// variables.
class CheckpointReader {
 public:
  CheckpointReader(const std::string& filename, TF_Status* status);

  bool HasTensor(const std::string& name) const;
  const std::string DebugString() const;

  // Returns a map from variable names to their shapes.  Slices of a partitioned
  // tensor are combined into a single entry.