Shell Programming and Scripting

NR==1 {                            # Select first line = header 
   for (i=1; i<=NF; i++)           #    For every field i (NF is last field# ) 
      col_fields[$i] = i;          #       Memorize field# for column name ($i)
}	  

{                                  # Select every line             
   out = "";                       #    Initialize out valriable (used for line diplay) 
   for (i=1; i<=cols_count; i++) { #    For every selected columns
      col_hdr = cols[i];           #       get column name
      out = (i>1 ? out OFS : "") (col_fields[col_hdr] ? $(col_fields[col_hdr]) : "?" );
	                            #       Concatenate column value $(col_fields[col_hdr]
                                   #       to out variable with Output Field Separator 
   }                               #
   print out;                      #    Print columns
}