Okay, I apologize Don, I am having a hard time getting this across. Hopefully I can answer some the of questions.

1. Will you guarantee that all timestamps in both of the files that will ever be processed on the same calendar date? Or, are there two date fields that have to be processed? Yes, both files will always be processed with the same calendar date because they are ran almost simultaneously. Yes, only because fields 16 thru 21 (some fields are duplicated because of the RAW field) fields are the time (epoch) that our telemetry extractor converts and then creates field 1 timestamp. My example stopped at field 18 because my real files have about 600 fields and data points. So technically there are 3 time fields - Day Of Year, time in milliseconds, time in microseconds. I said filed 21 in an earlier post because there were 3 added fields in newer files. In these particular files, they don't have these extra fields, but as long as I chose the correct msec field, my sort works properly.
CCSDS_DOY,CCSDS_DOY(RAW),CCSDS_MSEC
20550,20550,67522104


2. If there are two date fields (presumably fields 17 and 18 in the sample files in post #29), are those two date fields always adjacent in the input files? Yes, all the date fields 16-21 are always adjacent in both files.

3. And, repeating a question that has already been asked twice: Will the date field (or fields) used in file1 be the same as the field (or fields) used in file2? Yes, both files use the same time fields.

4. Will the milliseconds field in your files be set to the string 3600000 corresponding the exactly 1:00:00am or to the string 03600000 (i.e., are all values leading 0 padded to 8 digits, or are the values just the decimal number of milliseconds since midnight with no leading 0 fill)? (Note that the sort you were using in your examples sorting on field 21 would not work if that field does not have leading 0 fill.) It is an 8 digit decimal number.

5. Will you supply the field number(s) as parameters to your script, or are the field headings for the date field(s) in the two files constants that the script is supposed to find when reading the header lines? I only used the field numbers when I sorted off of the “msec” field (i.e sort -t -k,18,18 file1 file2) and that provided and accurate sort.

6. And, since at least one of the date fields is the last field in all of your sample input files, I will ask again: Are your input files in UNIX text file format or DOS text file format? (This might not matter on your system, but it does matter on the system I'm using to test my code.). These files are .csv files processed on a Linux platform.

7. If your input files are in DOS text file format, do you want output in DOS format or UNIX format? (DOS, UNIX, and don't care are valid answers to this question.) Unix format, but they will end up being .csv files after processing (not DOS).

8. And, obviously, supply us with the complete contents of your latest sample files (including some with different dates if the data in your real files won't always be for a single date) along with the expected output from those sample inputs. I will provide more when I get to a PC later or tomorrow. A couple of days ago, I tried sending my “real” files , but this site kept giving me errors when uploading.