How to count the number of consecutive identical lines

I have a file that looks like this:

2000 2000 2001 2001 2001 2001 2002 2002 

I need a script to show me this:

2000 - 2 2001 - 4 2002 - 2 

I prefer using sed or awk

1 Answer

This is precisely what uniq -c does. From man uniq:

DESCRIPTION

Filter adjacent matching lines from INPUT (or standard input), writing to OUTPUT (or standard output).

[ . . . ]

-c, --count
       prefix lines by the number of occurrences

So with your example, we get:

$ uniq -c file 2 2000 4 2001 2 2002 

You can also write a little script if you prefer for some reason. For instance, with awk:

$ awk '{ count[$0]++ } END{ for(line in count){ print line,count[line] }}' file 2000 2 2001 4 2002 2