You can use the following view...

SQL>desc all_tab_columns
 Name                            Null?    Type
 ------------------------------- -------- ----
 OWNER                           NOT NULL VARCHAR2(30)
 TABLE_NAME                      NOT NULL VARCHAR2(30)
 COLUMN_NAME                     NOT NULL VARCHAR2(30)
 DATA_TYPE                                VARCHAR2(9)
 DATA_LENGTH                     NOT NULL NUMBER
 DATA_PRECISION                           NUMBER
 DATA_SCALE                               NUMBER
 NULLABLE                                 VARCHAR2(1)
 COLUMN_ID                       NOT NULL NUMBER
 DEFAULT_LENGTH                           NUMBER
 DATA_DEFAULT                             LONG
 NUM_DISTINCT                             NUMBER
 LOW_VALUE                                RAW(32)
 HIGH_VALUE                               RAW(32)
 DENSITY                                  NUMBER
 NUM_NULLS                                NUMBER
 NUM_BUCKETS                              NUMBER
 LAST_ANALYZED                            DATE
 SAMPLE_SIZE                              NUMBER
[download]

Other views would be user_tab_columns and dba_tab_columns (if you have the privs)
DBI does have some methods (but the perldocs say they are experimental) to extract meta data (at least on the version I'm using it says it's experimental).