sort on part of the line, keep order on tie

Question

I would like to order some output of git log by date (not by time)

Unfortunately it seems to be impossible to sort only by some characters, ignoring the rest of the line with sort. What I tried so far:

Input: git-log.txt

git log --date-order --reverse --show-all --pretty="%ai#%h %s"

2013-08-22 09:54:12 +0200#f03fec1 G  
2013-08-21 10:43:57 +0200#c026cd6 A
2013-08-21 10:49:58 +0200#4630c3f B
2013-08-21 11:14:42 +0200#6e7141d C
2013-08-21 13:02:59 +0200#23ab0a8 D
2013-08-21 10:39:23 +0200#06b83f7 E
2013-08-21 14:10:16 +0200#f53384e F
2013-08-20 16:22:33 +0200#12591fb Z

naiv: This will sort perfectly including date

sort -k 1.1,1.10 git-log.txt

tricking by solving ties with not existing column

sort -k 1.1,1.10 -k 200 git-log.txt

tricking it to interpret whole line as single column with not existing separation character

sort -k 1.1,1.10 -t "^" git-log.txt

in all cases, output is:

2013-08-20 16:22:33 +0200#12591fb Z
2013-08-21 10:39:23 +0200#06b83f7 E
2013-08-21 10:43:57 +0200#c026cd6 A
2013-08-21 10:49:58 +0200#4630c3f B
2013-08-21 11:14:42 +0200#6e7141d C
2013-08-21 13:02:59 +0200#23ab0a8 D
2013-08-21 14:10:16 +0200#f53384e F
2013-08-22 09:54:12 +0200#f03fec1 G

I need (see the position of commit E)

2013-08-20 16:22:33 +0200#12591fb Z
2013-08-21 10:43:57 +0200#c026cd6 A
2013-08-21 10:49:58 +0200#4630c3f B
2013-08-21 11:14:42 +0200#6e7141d C
2013-08-21 13:02:59 +0200#23ab0a8 D
2013-08-21 10:39:23 +0200#06b83f7 E
2013-08-21 14:10:16 +0200#f53384e F
2013-08-22 09:54:12 +0200#f03fec1 G

How to teach sort to keep sort order on a tie? I can add any needed character the output...

Answer 1

You seem to be looking for -s option for sort:

   -s, --stable
          stabilize sort by disabling last-resort comparison

Say

sort -k 1.1,1.10 -t "^" -s git-log.txt

instead.

Answer 2

Note also the sort --debug option to help with this (it would have made the second problematic sort obvious in this case)