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Full Discussion: awk to compare flat files and print output to another file
Top Forums Shell Programming and Scripting awk to compare flat files and print output to another file Post 302432559 by suhaeb on Friday 25th of June 2010 10:18:34 AM
Old 06-25-2010
Thanks for your time on this, its much appreciated

1) Do both files have exactly the same number of records and are you just looking for records which have changed? Does the order of the output into file3 matter?

File1 has 1803077 records
file2 has 1795370 records

2) If there can be more or less records in file2 than file1, does the order of the output into file3 matter?

I would prefer 1st row in file3 from file1 and 2nd row from file2 and so on

Are you also interested in records which exist in file1 but do not exist in file2?

Yes, and viceversa also, it would be good if we can copy the records to diffrent files say recordsonlyonfile1.txt and recordsonlyonfile2.txt

3) What percentage of differences do you expect? (This is really a performance question because some approaches would involve multiple lookups).

there are huge changes in the file it could be over 50%

4) If this proves too difficult for shell programming, do you have a mainstream database engine?

I have informix database I am not sure if this would not help me as there is no uniq key in the records



---------- Post updated at 15:05 ---------- Previous update was at 14:20 ----------

One shell approach if the order of the output does not matter.
Tried with two approx 5 million record files of 500 Mb each. Took about 5 mins to run and the output only shows the mismatched records from file2. Actual performance will depend on how fast you computer is and how much memory you can give to sort.

Code:
#!/bin/ksh
cat file1 | sort > sortfile1
cat file2 | sort > sortfile2
comm -13 sortfile1 sortfile2

When sorting large files be sure to set $TMPDIR to somewhere with enough space for at least twice the size of the file being sorted.[/QUOTE]
 

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LEARN ABOUT OSX

opendiff

opendiff(1)						    BSD General Commands Manual 					       opendiff(1)

NAME

     opendiff -- Use FileMerge to graphically compare or merge file or directories

SYNOPSIS

     opendiff file1 file2 [-ancestor ancestorFile] [-merge mergeFile]
     opendiff dir1 dir2 [-ancestor ancestorDirectory] [-merge mergeDirectory]

DESCRIPTION

     opendiff is a command line utility that provides a convenient way to launch the FileMerge application from Terminal to graphically compare
     files or directories.  If FileMerge is already running, opendiff will connect to that running instance for the new comparison.  opendiff
     exits immediately after the comparison request has been sent to FileMerge.

     opendiff and FileMerge can be used to compare two files file1 and file2 or to compare two directories dir1 and dir2.

     If the -ancestor flag is given, FileMerge will compare the two files or directories to a common ancestor.	This is useful if two people inde-
     pendently modify copies of a single original file or directory.

     FileMerge lets you merge two files or directories together to create a third file or directory.  To see the contents of a merged file, drag
     the splitter bar at the bottom of FileMerge's file comparison window.  The contents of the merged file can be directly edited within File-
     Merge.  After editing, the merged file can be saved to the file (or into the directory) specified with the Fl merge flag.	If a destination
     is not specified with the -merge flag, FileMerge will ask for a destination file or directory when you try to save a merged file.

     For further information, please consult the Help information available from the FileMerge application.

FILES

     /Developer/Applications/Utilities/FileMerge.app

     opendiff and FileMerge are installed as part of the Mac OS X Developer Tools.

SEE ALSO

     diff(1), diff3(1), cmp(1)

Mac OS X							  August 3, 2004							  Mac OS X
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