Read file name to regexp function

Hi,

Can somebody help me to modify the code below to obtain the output: matchStr = 'TRMM_1998_01_newntcl.csv

str = 'TRMM_1998_01_newntcl.csv';
expression = '\w*TRMM';
month_to_match = 1;  
str_for_month = sprintf('%02d', month_to_match);
matchStr = regexp(str,expression,'match');

[Walter Roberson]

duplicates http://uk.mathworks.com/matlabcentral/answers/215461-read-csv-files-by-regulare-expression-function