I have to add number in column 1 by month.

1531 Feb 1 2007 pgaps_p007_27909.trc
1529 Feb 1 2007 pgaps_p006_27907.trc
1533 Feb 1 2007 pgaps_p005_27905.trc
635 Apr 7 2007 pgaps_smon_2347.trc
634 Apr 7 2007 pgaps_lgwr_2343.trc
634 Apr 8 2007 pgaps_lgwr_2311.trc
613 Apr 10 2007 pgaps_p004_402.trc
615 Apr 10 2007 pgaps_p002_7500.trc
698 May 2 2007 pgaps_smon_2339.trc
634 May 5 2007 pgaps_lgwr_2335.trc
656 Mar 1 2007 pgaps_smon_8006.trc
634 Mar 3 2007 pgaps_lgwr_8002.trc
634 Mar 4 2007 pgaps_lgwr_2383.trc
641 Mar 8 2007 pgaps_qmn0_20351.trc

Output should be :
Feb 4593
Apr 3131
May 3897

When I run below awk command I am not getting desired output.

ls -ltr |awk 'BEGIN { OFS = "\t"; ORS = "\n\n" } { print $1, $2, $3, $4 }'| awk '{tot=tot+$1}END{print tot}'

Any help would be greatly appreciated.

I don't get that kind of output with ls -l but assuming you do, the following ought to work.

Requesting ls to sort the output is unnecessary, if you require chronological output order, some additional tricks will be needed. The array loop in awk for (x in y) traverses the keys of y in unpredictable order.

Also the sample output you posted doesn't seem to agree with the input. I get the following

Did I misunderstand your requirement, or is the sample output wrong? Looks like you accidentally summed Mar and May into the same category.

Era,
Thanks for the update. Your observation is absolutely correct. I removed first few colums of ls -ltr output as they are not needed in my script. When I run command provided by you I do not get intended output.

ls -l | awk '{ tot[$2] += $1 } END { for (t in tot) printf "%s\t%i\n", t, tot[t] }'

354272 %ii
1 %ii

Thanks,
Prakash

The real column numbers are $5 and $6 then, if your ls gives the same output format as mine.

Era,
Thanks for your help. I am able to get output as desired.