FILE_LIST enables you to get a string array infil with all the files
that fulfill a set of specifications by typing:
IDL> infil = file_list(dir, filenam)
IDL> infil = file_list(dir, filenam, /cd)
where dir is a string array of directory name(s) and filenam is a string with the file designation (wild cards are ok - e.g., sfd* or bda920101.*).