Understand Unix Diff Command

Question

I am trying to find the difference between two files, where-in i would like to know the new entries in file_2. For ex :

If a.txt contains:

a
b
c

And b.txt contains:

c
d
f

I would like to get d and f

I'm using the command : diff --changed-group-format="%>" --unchanged-group-format=''

mymach@dev-machine:~/test$ grep 'C:/Documents and Settings/pandep2/AppData/Local/Google/Chrome/User Data/CrashpadMetrics.pma~RF115cef5.TMP' file_1.log
C:/Documents and Settings/pandep2/AppData/Local/Google/Chrome/User Data/CrashpadMetrics.pma~RF115cef5.TMP

mymach@dev-machine:~/test$ grep 'C:/Documents and Settings/pandep2/AppData/Local/Google/Chrome/User Data/CrashpadMetrics.pma~RF115cef5.TMP' file_2.log
C:/Documents and Settings/pandep2/AppData/Local/Google/Chrome/User Data/CrashpadMetrics.pma~RF115cef5.TMP

mymach@dev-machine:~/test$ diff --changed-group-format="%>" --unchanged-group-format='' file_1.log file_2.log >diff_file.log

mymach@dev-machine:~/test$ grep 'C:/Documents and Settings/pandep2/AppData/Local/Google/Chrome/User Data/CrashpadMetrics.pma~RF115cef5.TMP' diff_file.log
C:/Documents and Settings/pandep2/AppData/Local/Google/Chrome/User Data/CrashpadMetrics.pma~RF115cef5.TMP

Since, the same file existed in both files, why would diff command still report that file?

$ echo "C:/Documents and Settings/pandep2/AppData/Local/Google/Chrome/User Data/CrashpadMetrics.pma~RF115cef5.TMP" > file_1.log $ cp file_1.log file_2.log $ diff --changed-group-format="%>" --unchanged-group-format='' file_1.log file_2.log $ It should work. Your files obviously aren't matching — bob dylan
– bob dylan, Commented Jun 14, 2018 at 11:08
I never thought that location does play an important role, i always thought diff doesn't need a sorted file ? — PanDe
– PanDe, Commented Jun 14, 2018 at 11:15
does anyone have a better solution than diff for such scenario? I would really appreciate that.... i have two files which contain more than 1 million entries in each and i would like to find the difference of them. — PanDe
– PanDe, Commented Jun 14, 2018 at 11:31
i found a command : bash -c 'diff --changed-group-format="%>" --unchanged-group-format='' <(sort file_1.log) <(sort file_2.log) > diff_file.log' is this good ? — PanDe
– PanDe, Commented Jun 14, 2018 at 11:38

PanDe · Accepted Answer · 2018-06-14 16:29:03Z

1

In such scenario's, we are better of using the comm command in Unix.

for the above scenario, i have used:

comm -23 <(sort file_1.txt) <(sort file_2.txt)

This would give the unique files of file_1.txt

comm -13 <(sort a.txt) <(sort b.txt)

This would give the unique files of file_2.txt

comm -12 <(sort a.txt) <(sort b.txt)

This would give the common files between both files

answered Jun 14, 2018 at 16:29

PanDe

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