I'm looking at migrating a large suite of IBM Assembler Language programs, from a vcs based on "filenames include version numbers", to a modern vcs which will give me, among other things, the ability to branch and merge. 

These files have 80-column records, the last 8 columns being an almost-meaningless sequence number. 

For a number of reasons which I don't really want to waste space by going into, I need the vcs to ignore (but hopefully preserve in some well-defined manner) the sequence number columns, and to diff and patch based only on the contents of the first 72 columns.

Any ideas? 

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Just to clarify "ignore but preserve": I accept it's a bit vague, as I haven't fully collected my ideas yet.

It would be something along the lines of this: 

> 
> "When merging/patching, if one side has sequence numbers, output them; if more-than-one side has sequence numbers, use those present in file (1|2|3)" 
> 
> 
> 

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Why do I want to preserve sequence numbers? First, they really *are* sequence numbers. Second, I want to reintegrate this stuff back onto the mainframe, where sequence numbers can be terribly significant. (Those of you who know what "SMP/E" means will understand. Those who don't, be happy, but tremble...)

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I've just realised I hadn't accepted an answer. Difficult choice, but @Noldorin comes closest to where I have to go.