How to extract date and time from a string? (In this case the string happens to be the name of a HDF5-file.)
First something simple
str = 'GOME_O3-NO2-NO2Tropo-BrO-SO2-H2O-HCHO_L2_20070123202633_051_METOPA_01366_DLR_03.HDF5';
dti = regexp( str, '\d{14}', 'match', 'once' );
datestr( datenum( dti, 'yyyymmddHHMMSS' ), 'yyyy-mm-dd HH:MM:SS' )
ans =
2007-01-23 20:26:33
This code assumes that the first appearance of fourteen consecutive digits represents date and time. However, is that guaranteed? If not, is there some other characteristics of the string that can be used? Furthermore, is it guaranteed that the string of digits honors the pattern, 'yyyymmddHHMMSS'?
It's possible to create a regular expression, which take advantage of the fact that not all digits can appear in all positions, e.g minutes and second are constrained by the interval [00,59].
 
A bit more selective:   Assume that it's guaranteed that
- the first appearance of exactly fourteen consecutive digits surrounded by underscore, "_", represents date and time.
- the string of digits honors the pattern, 'yyyymmddHHMMSS'
If so replace the expression, '\d{14}', by '(?<=_)\d{14}(?=_)'
