UNIX Command Line

Following example will show how we can use UNIX paste and join command with awk to find difference of two numeric columns of two similar files.

e.g. Input file:

$ cat file1.txt 
Aug-1,100
Aug-2,220
Aug-4,230
Aug-5,100

$ cat file2.txt 
Aug-1,100
Aug-2,120
Aug-4,400
Aug-5,250

Required output:
As you can see both file1.txt and file2.txt has got first field (comma separated) in the same order. We will have to find out the corresponding (2nd field of file1.txt - 2nd field of file2.txt) and the output required is something like this:

Aug-1,100,100,0
Aug-2,220,120,100
Aug-4,230,400,-170
Aug-5,100,250,-150

Solution#1:

$ paste -d "," file1.txt file2.txt
Aug-1,100,Aug-1,100
Aug-2,220,Aug-2,120
Aug-4,230,Aug-4,400
Aug-5,100,Aug-5,250

$ paste -d "," file1.txt file2.txt | awk 'BEGIN {FS=OFS=","} {print $1,$2,$NF,$2-$NF}'
Aug-1,100,100,0
Aug-2,220,120,100
Aug-4,230,400,-170
Aug-5,100,250,-150

Solution#2:

$ join -t, -1 1 -2 1 file1.txt file2.txt 
Aug-1,100,100
Aug-2,220,120
Aug-4,230,400
Aug-5,100,250

$ join -t, -1 1 -2 1 file1.txt file2.txt | awk ' BEGIN {FS=OFS=","} {print $0,$2-$NF}'
Aug-1,100,100,0
Aug-2,220,120,100
Aug-4,230,400,-170
Aug-5,100,250,-150

Some similar posts:
- A small tutorial on UNIX paste command
- Performing join using awk
- Join in bash
- Perform outer join in UNIX Bash
- Find diff based on field - UNIX Bash