# _CP_atvar

The _CP_atvar function reads and writes D3 shell variables. It is
 equivalent to the BASIC u91 user exit.

## Syntax

```
 _CP_atvar(CPSTR ** result, CPSTR * input)
```

## Parameter(s)

| result | The result from processing the input parameter. |
| --- | --- |
| input | This parameter can take on the following four forms: Null string: Returns the names of all D3 shell variables as an attribute mark delimited list. var.name: Returns the value associated with the specified variable. var.name^value: Attribute mark delimited name and value. This assigns the given value to the specified variable. var.name]: Name followed by value mark. This deletes the specified variable. |

## Description

This function returns:

- 0: Success

- -1: Error

## Example(s)

```

 CPSTR * AM = _CP_mkstrl("\xfe", 1);
 CPSTR * VM = _CP_mkstrl("\xfd", 1);
 CPSTR * connectionType = _CP_mkstr("CONNECTIONTYPE");
 CPSTR * connectionTypeValue = _CP_mkstr("web interface");
 CPSTR * input = _CP_str_null;;
 CPSTR * result = _CP_str_null;

 // Display existing D3 shell variable names.
 if (_CP_atvar(&result, _CP_str_null) == 0) _CP_print(result);

 // Set the D3 shell variable called CONNECTIONTYPE to "web interface".
 _CP_cat(&input, connectionType, AM);
 _CP_cat(&input, input, connectionTypeValue);
 if (_CP_atvar(&result, input) == 0) _CP_print(result);

 // Display existing D3 shell variable names, followed by the value of the CONNECTIONTYPE variable.
 if (_CP_atvar(&result, _CP_str_null) == 0) _CP_print(result);
 if (_CP_atvar(&result, connectionType) == 0) _CP_print(result);

 // Delete the CONNECTIONTYPE variable then the display the remaining D3 shell variables.
 _CP_cat(&input, connectionType, VM);
 if (_CP_atvar(&result, input) == 0) _CP_print(result);
 if (_CP_atvar(&result, _CP_str_null) == 0) _CP_print(result);

 _CP_str_free(input);
 _CP_str_free(connectionType);
 _CP_str_free(connectionTypeValue);
```

## See also

- [@ shell variable](https://d3codex.com/tcl/shell-variable/)
- [C functions overview](https://d3codex.com/cfunctions/c-functions-overview/)
- [penv command](https://d3codex.com/tcl/penv-command/)
- [set command](https://d3codex.com/tcl/set-command/)
- [u91 user exit](https://d3codex.com/pickbasic-flashbasic/u91-user-exit/)
- [unset command](https://d3codex.com/tcl/unset-command/)

---
Source: https://d3codex.com/cfunctions/cp-atvar/ - part of the D3Codex reference.