Sorting and Counting output in Linux shell

Sometimes we need to make some operations on commands output in Linux. Very intensive operation on output I do is sorting and counting. For the sake of an example - every time I setup a new equipment I make backup and save it in `back` directory, with the file-names like:

ls -1 back  |  head -n3

101-back-2017-02-21

102-back-2017-03-01

106-back-2017-02-21

Where numbers at the starting of the names of the backups are branch codes.

When I want to learn how many equipment was installed I can simply do:

ls back | wc -l

98

But this is total number of all configured equipment. what if I want to find how much equipment I setup every month?

Let's go:

1. we need to list all files in `back` directory along with their creation times:
1. ll back/ 
2. now we need to select only month (6 column) and print it:
1. ll back/ | awk '{print $6}'
3. now we need to sort output alphabetically:
1. ll back/ | awk '{print $6}' | sort
4. we needed sorting because uniq command filtering matching adjacent lines and then making operations according to specified options:
1. ll back/ | awk '{print $6}' | sort | uniq
1. 
   
2. Feb
3. Mar
2. we'll use `-c` which makes `uniq` count all occurrences of unique values  (Mar and Feb in our case) in the output:
1. ll back/ | awk '{print $6}' | sort | uniq -c
1. 1
2. 60 Feb
3. 38 Mar
2. You see line which count is `1` this is because of the `ll` commands `total` first line, to avoid this you can use:
1.  ll back/ | grep -v total | awk '{print $6}' | sort | uniq -c
5. If you need to view results per day of the month additional use 7th column (use "-" to see `-` as month and day of the month delimiter):
1. Sorting using default `sort` settings
2. ll back/ | grep -v total | awk '{print $6 "-" $7}' | sort | uniq -c
1. 1 Feb-20
2. 59 Feb-21
3. 23 Mar-1
4. 9 Mar-2
5. 6 Mar-7
3. Soring using day of the month and numeric sorting with `-` delimiter (to sort in reverse order, use `-r` option > '-k2nr' instead of `-k2n`):
4. ll back/ | grep -v total | awk '{print $6 "-" $7}' | sort -t"-" -k2n | uniq -c
1. 23 Mar-1
2. 9 Mar-2
3. 6 Mar-7
4. 1 Feb-20
5. 59 Feb-21