With GNU sed
you can specify the occurrence of the match so where s/ +/ /g
would single space the whole file s/ +/ /2g
single spaces the whole file but after the second match on each line:
$ column -t file | sed -re 's/: ( +)/\1: /' -e 's/ +/ /2g'
session1 : 3 windows (created Fri Sep 20 13:16:13 2013) [157x56]
stuff : 3 windows (created Fri Sep 20 13:25:21 2013) [157x56]
asdf : 2 windows (created Sun Sep 29 23:06:33 2013) [77x17] (attached)
website : 1 windows (created Tue Sep 24 17:22:14 2013) [157x26]
To sort out the first columns spacing we use s/: ( +)/\1: /
to match all the spaces from the :
and we store n-1 spaces in the first capture group. We then replace the :
and all the spaces with n-1 spaces followed by a :
followed by a space (making n total space again).