Find the common beginning substring in an array of strings

[technojosh]

I have a group of strings, that all share a common beginning substring. This substring will not always be identical, the only thing I know is that in any given array of strings, there *will* be a common substring at the beginning.

Context: As of today, I have a reporting script that will produce an HTML table, row-by-row, of a set of tests. I want to show a "header" row, that displays the test category, and this is found in the substring problem I mention above.

Two example sets of strings:

my @array_of_test_names = (
    'History - Family History - Suite with Patient - Clinic - Select R
+emove(-) Icon of Relative. - Clinic',
    'History - Family History - Suite with Patient - Clinic - Save aft
+er Entering values in all fields - Clinic',
    'History - Family History - Suite with Patient - Clinic - Select A
+dd(+) Icon of Relative. - Clinic',
    'History - Family History - Suite with Patient - Clinic - Multiple
+ selection of relatives - Clinic',
    'History - Family History - Suite with Patient - Clinic - Interact
+ion Checking message not provided if procedure code is selected - Cli
+nic',
    'History - Family History - Suite with Patient - Clinic - Interact
+ion Checking message provided if no procedure code is selected - Clin
+ic'
);

my @second_sample_array = (
    'WorkCenter - List Patients - To check the items displayed in Filt
+er By combo box',
    'WorkCenter - List Patients - To check Filter By combo box when no
+ patients are assigned on initial login',
    'WorkCenter - List Patients - Order in which patients are displaye
+d'
);

Any guidance on how to capture a common beginning substring would be greatly appreciated.