Convert unix timestamp to date
# date -d @1221256800 "+%Y-%m-%d %T" 2008-09-13 00:00:00
Convert a date (YYYYMMDD) to unix timestamp
# date -d "20080913" +%s 1221256800
A chronological documentation test project, nothing serious, really!
# date -d @1221256800 "+%Y-%m-%d %T" 2008-09-13 00:00:00
# date -d "20080913" +%s 1221256800