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Top Forums Shell Programming and Scripting Compare two big files for differences using Linux Post 303001960 by shanul karim on Tuesday 15th of August 2017 12:24:24 PM
Old 08-15-2017
Compare two big files for differences using Linux

Hello everybody

Looking for help in comparing two files in Linux(files are big 800MB each).

Example:-

File1 has below data
$ cat file1
5,6,3
2.1.4
1,1,1
8,9,1

File2 has below data
$ cat file2
5,6,3
8,9,8
1,2,1
2,1,4

Need Output as below
8,9,8
1,2,1
1,1,1
8,9,1

tried below awk command but it giving below output which is not correct
$ awk 'NR==FNR{a[$0]++;next} !a[$0]' file2 file1
2.1.4
1,1,1
8,9,1

$ cat vlookup.awk
FNR==NR{
a[$1]=$2
next
}
{ if ($1 in a) {print $1, a[$1]} else {print $1, "NA"} }

awk -f vlookup.awk file2 file1 | column -t
$ awk -f vlookup.awk file2 file1 | column -t
5,6,3
2.1.4 NA
1,1,1 NA
8,9,1 NA

treid below do while loop with grep command but its taking lot of time.

$ cat scp.sh
rm -f newfile.txt
while read line
do
line1=`grep -ie "${line}" file1`
if [ $? -ne 0 ] ; then
echo "$line" >> file2
fi
done <CUDB_REF

./scp.sh
8,9,8
1,2,1

This is correct but taking very long time for big file

Pls suggest better way which is fast.
Image
 

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diff3(1)						      General Commands Manual							  diff3(1)

Name
       diff3 - 3-way differential file comparison

Syntax
       diff3 [-ex3] file1 file2 file3

Description
       The command compares three versions of a file, and publishes the ranges of text that disagree, flagged with the following codes:

	  ====	      all three files differ

	  ====1       file1 is different

	  ====2       file2 is different

	  ====3       file3 is different

       The type of change needed to convert a given range of a given file to some other is indicated in one of these ways:

	  f : n1 a    Text is to be appended after line number n1 in file f, where f = 1, 2, or 3.

	  f : n1 , n2 c
		      Text is to be changed in the range line n1 to line n2.  If n1 = n2, the range may be abbreviated to n1.

       The original contents of the range follows immediately after a c indication.  When the contents of two files are identical, the contents of
       the lower-numbered file is suppressed.

Options
       -3   Produces an editor script containing the changes between file1 and file2 that are to be incorporated into file3.

       -e	   Produces an editor script containing the changes between file2 and file3 that are to be incorporated into file1.

       -x	   Produces an editor script containing the changes among all three files.

Examples
       Under the -e option, publishes a script for the editor that incorporates into file1 all changes between file2 and  file3  -  that  is,  the
       changes	that would normally be flagged ==== and ====3.	Option -x (-3) produces a script to incorporate only changes flagged ==== (====3).
       The following command applies the resulting script to `file1':
       (cat script; echo '1,$p') | ed - file1

Restrictions
       Text lines that consist of a single `.'	defeat -e.

Files
       /tmp/d3?????
       /usr/lib/diff3

See Also
       cmp(1), comm(1), diff(1), dffmk(1), join(1), sccsdiff(1), uniq(1)

																	  diff3(1)
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