file comparison

Dave Angel davea at
Fri Jul 31 14:55:27 CEST 2009

Hendrik van Rooyen wrote:
> On Friday 31 July 2009 11:25:17 learner learner wrote:
>> Hi all,
>> I want to compare two text files line by line and eliminate the
>> matching/repeated line and store the unmatched/leftout lines into a third
>> file or overwrite into one of them.
> This is not as simple as it seems.
> You will probably be better off using diff, or,
> if it is a learning exercise, studying its source.
> - Hendrik

It is not only "not simple," it's totally underspecified.


If this is a homework assignment, you should read the whole assignment, 
and see what it says.  Without knowing something about the text files, I 
couldn't even guess what the real goal is.

For example, if the text files are really text (e.g. a letter to 
grandma), then we want a context-sensitive comparison, the kind that 
Windiff, RCSDiff, DiffMerge, and others can do.

If the text files are each a list of items, with order and duplication 
irrelevant, then your best bet is probably to build a set from each, and 
difference the sets.


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