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Top Forums Shell Programming and Scripting Comparing two files and appending only missing lines. Post 302186330 by era on Thursday 17th of April 2008 02:25:53 AM
Old 04-17-2008
Let's say we have a file. Call it "version 1". Then you copy it to another place, and make some edits. Call this "version 2a". Then copy it to yet another place, and make some different edits. Call this "version 2b".

Now, the simple way to merge changes from 2a to 2b is to find the difference between 1 and 2a, and apply that to 2b.

Code:
diff -u version1 version2a >diff2a
cd ../path/to/2b
patch -p0 <../back/to/diff2a

The patches produced by diff have absolute line numbers etc so you cannot blindly apply them. patch is able to introduce "fuzz" so it can squeeze a patch into place even if some changes have happened in the file.

If there are conflicts, of course, you still need to resolve them.

A version control system probably helps if you need to do this often.
 

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GENDIFF(1)						      General Commands Manual							GENDIFF(1)

NAME
gendiff - utility to aid in error-free diff file generation SYNOPSIS
gendiff <directory> <diff-extension> DESCRIPTION
gendiff is a rather simple script which aids in generating a diff file from a single directory. It takes a directory name and a "diff- extension" as its only arguments. The diff extension should be a unique sequence of characters added to the end of all original, unmodi- fied files. The output of the program is a diff file which may be applied with the patch program to recreate the changes. The usual sequence of events for creating a diff is to create two identical directories, make changes in one directory, and then use the diff utility to create a list of differences between the two. Using gendiff eliminates the need for the extra, original and unmodified directory copy. Instead, only the individual files that are modified need to be saved. Before editing a file, copy the file, appending the extension you have chosen to the filename. I.e. if you were going to edit somefile.cpp and have chosen the extension "fix", copy it to somefile.cpp.fix before editing it. Then edit the first copy (somefile.cpp). After editing all the files you need to edit in this fashion, enter the directory one level above where your source code resides, and then type $ gendiff somedirectory .fix > mydiff-fix.patch You should redirect the output to a file (as illustrated) unless you want to see the results on stdout. SEE ALSO
diff(1), patch(1) AUTHOR
Marc Ewing <marc@redhat.com> 4th Berkeley Distribution Mon Jan 10 2000 GENDIFF(1)
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