I have a file as the following     200.000    1.353    0.086  200.250    1.417    0.000  200.500    1.359    0.091  200.750    1.423    0.000  201.000    1.365    0.093  201.250    1.427    0.000  201.500    1.373    0.093  201.750    1.432    0.000  202.000    1.383    0.091  202.250    1.435    0.000  202.500    1.392    0.087  202.750    1.436    0.000  203.000    1.402    0.081  203.250    1.437    0.001  203.500    1.412    0.073  204.000    1.423    0.065  204.500    1.432    0.055  205.000    1.441    0.045  I would like to grep only the rows that have in the first column the decimal .000 and .500 only so the output would be like this  200.000    1.353    0.086  200.500    1.359    0.091  201.000    1.365    0.093  201.500    1.373    0.093  202.000    1.383    0.091  202.500    1.392    0.087  203.000    1.402    0.081  203.500    1.412    0.073  204.000    1.423    0.065  204.500    1.432    0.055  205.000    1.441    0.045  
How to grep rows that have certain value in a specific column?
grep