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Full Discussion: Restricted File Comparison
Top Forums Shell Programming and Scripting Restricted File Comparison Post 302554713 by salamagd on Monday 12th of September 2011 08:32:49 PM
Old 09-12-2011
Restricted File Comparison

Hey guys,

I've got a scripting problem that has been bugging me so thought I'd ask the wise people here! Basically I have two overlapping log files, and I want to get the newest lines from the new log file that aren't in the old log file - but not the old lines in the old log that aren't in the new log.

Say the old log file has this content:
Code:
1: Apple
2: Banana
3: Carrot
4: Dog

And the new log has this content:
Code:
3: Carrot
4: Dog
5: Elephant
6: Fish

I want my script to output:
Code:
5: Elephant
6: Fish

Essentially, I want a diff of the two files, but only include the lines that are unique to the second file - is this possible?

edit: It seems that I can do it with "grep -v -x -f file1 file2", but this has O(n^2) complexity so won't work nearly fast enough with files that are reasonably long. Any other ideas?

Thanks for any help!
Giancarlo
 

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DIFF(1) 						      General Commands Manual							   DIFF(1)

NAME
diff - print differences between two files SYNOPSIS
diff [-c | -e | -C n] [-br]file1 file2 OPTIONS
-C n Produce output that contains n lines of context -b Ignore white space when comparing -c Produce output that contains three lines of context -e Produce an ed-script to convert file1 into file2 -r Apply diff recursively to files and directories of EXAMPLES
diff file1 file2 # Print differences between 2 files diff -C 0 file1 file2 # Same as above diff -C 3 file1 file2 # Output three lines of context with every diff -c file1 file2 # Same diff /etc /dev # Compares recursively the directories /etc and /dev diff passwd /etc # Compares ./passwd to /etc/passwd DESCRIPTION
the same name, when file1 and file2 are both directories" difference encountered" Diff compares two files and generates a list of lines telling how the two files differ. Lines may not be longer than 128 characters. If the two arguments on the command line are both directories, diff recursively steps through all subdirectories comparing files of the same name. If a file name is found only in one directory, a diagnostic message is written to stdout. A file that is of either block special, character special or FIFO special type, cannot be compared to any other file. On the other hand, if there is one directory and one file given on the command line, diff tries to compare the file with the same name as file in the directory directory. SEE ALSO
cdiff(1), cmp(1), comm(1), patch(1). DIFF(1)
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