>> A = {'file.m', 'file.log', 'file_dsaf_dsfaf.log', 'data.log'};
>> idx = cellfun('isempty',regexp(A,'^fi.*log$'));
>> B = A(~idx)
B =
'file.log'
'file_dsaf_dsfaf.log'
Note that if you are using dir to get the file data then it would be much simpler and more efficient to filter the filenames using dir and the wildcard operator *:
S = dir('fi*.log');
B = {S.name}
