'''diff''' utilities determine and present the differences between texts.



** See Also **

   [comparing files in tcl]:   

   [Using Snit to glue diff, patch, and md5sum]:   



** Tcl Tools **

   [diff in Tcl]:    

   [Another diff in Tcl]:   

   [DiffUtilTcl]:   

   [tkdiff]:   

   [eskil]:   A very nice graphical diff tool.

   [bindiff]:   



** Non-Tcl Tools **

   [http://formulasoft.com/afc.html%|%Active File Compare]:   Proprietary.  [CL] has received mild testimonials.  There's no particular Tcl connection; it's just been valuable to me as a Tcl developer when working under Windows.

   [http://winmerge.org/%|%WinMerge]:   Open-source, for Windows.  A future cross-platform version is planned. 

   [http://xdelta.org/%|%xdelta]:   Open-source binary diff, differential compression tools, VCDIFF (RFC 3284) delta compression Jean-Samuel Gauthier:  ...supports a simple but flexible callback interface to feed/extract data to/from the compressor.  Tcl Examples included.



** description **

Most frequently, '''diff'' is a comparison of two files.  When the output is
text, the Unix tradition is to display the differences in terms of the changes
made to the first file to achieve a file similar to the second file.

Often in a [GUI] application, coloring or other techniques are used
to convey more information about what changed.  In some applications, entire
lines are highlighted, while in other, particular characters are highlighted.



** Specialized Diff **

[Arjen Markus]: We have faced a slightly different problem: two files that should be compared with special care for (floating-point) numbers. The solution was simple in design:

   * Read the files line by line (all lines should be comparable, we did not need to deal with inserted or deleted lines)
   * Split the lines into words and compare the words as either strings or as numbers.
   * By using [[string is float]] we identified if the "word" is actually a number and if so, we compared them numerically (even allowing a certain tolerance if required).

This way you are immune to numbers formatted in different ways:
0.1, +.1, 1.0E-01, +1.00e-001 all spell the same number and you can encounter all of these forms (sometimes you have less than perfect control over the precise format).

----

[Arjen Markus]: Question: would not this be a nice addition for the fileutil module in Tcllib?

[GPS]: maybe it would...

[Arjen Markus]: If so, it would benefit (in my opinion) from two custom procedures:

   * A procedure one can supply to compare the lines (for instance: ignore white-space or interpret numbers as numbers - my original problem)
   * A procedure to process the output (in a manner as [Tkdiff] does for instance)

----

[Arjen Markus]: A few thoughts for improving the performance:

   * Store the lines as {lineno content}
   * Sort by content (lsort has this ability via "-index")
   * Use binary search to replace the inner loop.

This would bring back the number of iterations from O(N^2) to O(NlogN).
But perhaps it is not worth the trouble :-)


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