PHP shm_remove_var() removes a stored variable from a shared-memory segment without deleting the entire segment. The examples below show how the call behaves, where it is useful, and which limitations matter.
What Is shm_remove_var() in PHP?
Removes a stored variable from a shared-memory segment without deleting the entire segment.
Its call structure is:
shm_remove_var($shm, $key)The arguments identify the values or resources passed to shm_remove_var(). Read the examples with attention to the type of each supplied argument and to whether the function modifies its input or returns a separate result.
Requires the corresponding System V shared-memory or SHMOP extension and suitable operating-system support. IPC keys used below are illustrative; use coordinated, environment-appropriate keys in real deployments.
Example 1: Basic Usage
This example introduces shm_remove_var with a direct call and a small, readable input.
<?php
$memory = shm_attach(0x12441, 4096, 0600);
if ($memory !== false) { shm_put_var($memory, 2, "temporary"); shm_remove_var($memory, 2); shm_detach($memory); }Removes a stored variable from a shared-memory segment without deleting the entire segment. You must supply the variable key, not the segment IPC key.
Example 2: Another Behavior or Input
Compare this input with the previous example: changing the data or option can affect how shm_remove_var behaves.
<?php
$memory = shm_attach(0x12442, 4096, 0600);
if ($memory !== false && shm_has_var($memory, 4)) { var_dump(shm_remove_var($memory, 4)); }
if ($memory !== false) { shm_detach($memory); }The changed input illustrates why output may differ with the chosen values or environment. You must supply the variable key, not the segment IPC key.
Practical Example: Using the Feature
The following example incorporates shm_remove_var into a workflow. Values such as paths, connection handles and configuration options must come from trusted application settings.
<?php
$memory = shm_attach(0x12443, 4096, 0600);
if ($memory !== false) { shm_put_var($memory, 5, "cached"); if (shm_has_var($memory, 5)) { shm_remove_var($memory, 5); } shm_detach($memory); }In a real application, check each operation result, validate values before use and clean up acquired resources. You must supply the variable key, not the segment IPC key.
Important Behavior and Edge Cases
- Purpose: Removes a stored variable from a shared-memory segment without deleting the entire segment.
- Key limitation: You must supply the variable key, not the segment IPC key.
- Failure handling: Check return values and handle invalid inputs and unavailable operating-system or extension features where relevant.
Comparison With Related Functions
| Function or Approach | Best Fit |
|---|---|
shm_remove_var() | Removes a stored variable from a shared-memory segment without deleting the entire segment. |
shm_has_var() | Checks whether a System V variable key exists without changing the stored value. |
Common Beginner Mistakes
| Mistake | Correct Approach |
|---|---|
| You must supply the variable key, not the segment IPC key. | The correct approach depends on this behavior: You must supply the variable key, not the segment IPC key. |
| Ignoring errors or cleanup after the operation. | Validate inputs and check each result; close files, restore settings or release resources when the operation requires it. |
Key Takeaways
- Removes a stored variable from a shared-memory segment without deleting the entire segment.
- You must supply the variable key, not the segment IPC key.
- Use the examples as starting points, and adapt environmental paths, resources and permissions rather than assuming fixed results.
shm_remove_var is useful when its specific behavior fits the problem. The safest implementations combine the correct API with input validation, error checking and resource cleanup.