Question

I have 2 files with following text:

OldFile:

Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg_livecd-lv_root
                       18G  2.4G   15G  14% /
tmpfs                 590M  276K  590M   1% /dev/shm
/dev/sda1             485M   31M  429M   7% /boot

NewFile

Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg_livecd-lv_root
                       18G  2.7G   15G  14% /
tmpfs                 590M  264K  590M   1% /dev/shm
/dev/sda1             485M   31M  429M   7% /boot
/dev/sdb1             3.8G  1.1G  2.8G  28% /media/9C6F-1ECD

Now in output file I just want following line. as this is newly added.

/dev/sdb1             3.8G  1.1G  2.8G  28% /media/9C6F-1ECD

but instead I’m getting following output as one number is also changed from 2.4 to 2.7.

                        18G  2.7G   15G  14% /
/dev/sdb1             3.8G  1.1G  2.8G  28% /media/9C6F-1ECD

so this is creating problem for me. I just want completely newly added line.

Answer 1

First, put the parts you do want to compare onto the end, as so:

df -P | awk 'NR > 1 {print $1 ":" $6 "\t" $0 }' | sort >comm-test.1
df -P | awk 'NR > 1 {print $1 ":" $6 "\t" $0 }' | sort >comm-test.2

Then:

join -t $'\t' -j 1 -o 2.2 \
  <(comm -13 \
     <(cut -f1 comm-test.1) \
     <(cut -f1 comm-test.2)) \
  comm-test.2

Note the use of df -P to ensure that the output from df is not split onto multiple lines (as in your example).

By the way — obscuring your problem was supremely unhelpful. Please do not do this in the future.