headcount(file_name​, header_mark)

Return number of header lines in text file.

Many file-reading functions allow the user to specify a number of header lines to skip before reading in data. To facilitate reading from files with an unknown or varying number of header lines, this function opens a text file, counts the number of lines in the header block (defined by a header mark; default is '#''), and (always!) closes the file. This makes it easy to read in data with a single call.
For example:
raw = importdata(my_csv_file, ',', headcount(my_csv_file, '%'));
reads a csv table, automatically skipping lines starting with '%' in the beginning of the file. (Note: it is true that importdata(my_file) will try to infer delimiters and headers automatically, but it will often fail.)