Determining if a key exists

Now that we have a named dictionary with key/value pairs, it becomes necessary to determine if the given key exists. To accomplish this, Tcl provides the dict exists command. The syntax is as follows:

dict exists DictionaryValue key… key…

How to do it…

In the following example, we will create a dictionary containing a set of key/value pairs and then determine whether or not a specific key exists. Return values from the commands are provided for clarity. Enter the following command:

% set names [dict create 1 John 2 Mary 3 Paul]
1 John 2 Mary 3 Paul
% dict exists $names 3
1

How it works…

The dict exists command returns a Boolean value to indicate if the specified key exists in the dictionary referenced in name. A return value of 1 indicates that the key exists, while a return of 0 indicates that it does not. Be aware that this command will return an error if dictionaryValue does not reference an existing dictionary.