How to add number of identical line next to the line itself?

Question

I have file file.txt which look like this

a
b
b
c
c
c

I want to know the command to which get file.txt as input and produces the output

a 1
b 2
c 3

Answer 1

I think uniq is the command you are looking for. The output of uniq -c is a little different from your format, but this can be fixed easily.

$ uniq -c file.txt
      1 a
      2 b
      3 c