File rewriting: One line is greater than variable's max size. Workaround?

Question

I need to replace a single line in a file. Generally, this code works fine:

(The actual specifics on what this block is doing is not necessary for this question).

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Answer 1

You could solve this with pure batch!

:readLongLine
< longline.tmp (
    for /L %%n in (1 1 20) do set /p part[%%n]=
)

After this your line is splitted into the variables part[1] .. part[20]

Writing this to a new file you could use

:writeLongLine
 longLine2.tmp