#
# A sed example
# <2019-06-19 15:26:23 cmic>
#
After running algorithm A on a lot of data, I end up with a large list of files like

 dataset-directory/0001_data.csv
 dataset-directory/0002_data.csv
 dataset-directory/0002_A.csv
 dataset-directory/0003_data.csv
 dataset-directory/0003_A.csv
 dataset-directory/0004_data.csv
 dataset-directory/0005_data.csv
 dataset-directory/0005_A.csv
..

The astute observer will note that the file for algorithm A on data 0001 and 0004 are missing.
How can I get a list of all the numbers for which A didn’t succeed?

So all together this gives the following

   ls | sed '/A/{N;d;}'  #N appends a \n and  next line to pattern space; 
      	    		 #d delete pattern space and start a new cycle 

NB: Lines from input stream are placed into the pattern space (where they can be modified)
and then pattern space is sent to output stream. The hold spce can be used for temporary storage.
NB: 	- n or N read/append input to patern space
	- d delete the pattern space and start a new cycle
	- h (or H) copy pattern space to hold space
	- g (or G) copy hold space to pattern space
	- x exchange pattern space and hold space
    
See also https://catonmat.net/sed-one-liners-explained-part-one
and https://catonmat.net/sed-one-liners-explained-part-two
and man sed RTFM !!