gistfile1.rb

require 'poi'

# given an Excel spreadsheet whose first sheet (Sheet 1) has this data:
#    A  B  C  D  E        
# 1  4     A     2010-01-04
# 2  3     B     =DATE(YEAR($E$1), MONTH($E$1), A2)
# 3  2     C     =DATE(YEAR($E$1), MONTH($E$1), A3)
# 4  1     D     =DATE(YEAR($E$1), MONTH($E$1), A4)

workbook = POI::Workbook.open('spreadsheet.xlsx')
sheet = workbook.worksheets["Sheet 1"]
rows  = sheet.rows

# get a cell's value -- returns the value as its proper type, evaluating formulas if need be
rows[0][0].value # => 4.0
rows[0][1].value # => nil
rows[0][2].value # => 'A'
rows[0][3].value # => nil
rows[0][4].value # => 2010-01-04 as a Date instance
rows[1][4].value # => 2010-01-03 as a Date instance
rows[2][4].value # => 2010-01-02 as a Date instance
rows[3][4].value # => 2010-01-01 as a Date instance

# you can access a cell in array style as well... these snippets are all equivalent
workbook.sheets[0][2][2]          # => 'C'
workbook[0][2][2]                 # => 'C'
workbook.sheets['Sheet 1'][2][2]  # => 'C'
workbook['Sheet 1'][2][2]         # => 'C'

# you can access a cell in 3D cell format too
workbook['Sheet 1!A1']            # => 4.0

# you can even refer to ranges of cells
workbook['Sheet 1!A1:A3']         # => [4.0, 3.0, 2.0]

# if cells E1 - E4 were a named range, you could refer to those cells by its name
# eg. if the cells were named "dates"...
workbook['dates']                 # => dates from E1 - E4

# to get the Cell instance, instead of its value, just use the Workbook#cell method
workbook.cell('dates')            # => cells that contain dates from E1 to E4
workbook['Sheet 1!A1:A3']         # => cells that contain 4.0, 3.0, and 2.0