How to update a date in a file if applicable and increment the last digit by one if one writes to the file using Vim?

Question

Aim

The aim is to update a number in a file if one writes to a file using Vim. If the date resides in the file the date part should be left unchanged, but the last digit needs to be incremented by one.

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Attempts

Attempt 1

/home/user/.vimrc

autocmd BufWritePre /tmp/test :%s/\d\{10}/\=strftime("%Y%m%d00")/

/temp/test

4014122100

writing the file results in:

2014122100

"/tmp/test" 2L, 29C written

Attempt 2

/home/user/.vimrc

autocmd BufWritePre /tmp/test :%s/\d\{10}/\=strftime("%Y%m%d00")/
autocmd BufWritePre /tmp/test :%s/\d\{10}/\=submatch(0)+1

/temp/test

4014122100

writing the file results in:

2014122101

"/tmp/test" 2L, 29C written

Attempt 3

function! ChangeDateIfApplicableAndIncrementLastDigit()
  if !match(getline(1,"$"),strftime("%Y%m%d")) >= 0
    autocmd BufWritePre /tmp/test :%s/\d\{10}/\=strftime("%Y%m%d00")/
  endif
  autocmd BufWritePre /tmp/test :%s/\d\{10}/\=submatch(0)+1
endfunction

autocmd BufWriteCmd /tmp/test call ChangeDateIfApplicableAndIncrementLastDigit()

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Expected results

Number of writesExpected result
1                          2014122101     
2                          2014122102     
3                          2014122103     

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Current outcome

Number of writesCurrent outcome
1                          2014122101       
2                          2014122101       
3                          2014122101       

Answer 1

So, if I get you right, your first and second attempts show that the basic mechanism works, but you're struggling with putting everything together, right?!

The problem is with the BufWriteCmd; that hook is supposed to write the buffer contents on its own. The netrw plugin uses those to implement remote filesystem access, for instance. You just need to define a single BufWritePre hook for your function, and then act depending on whether you've found a current date:

function! ChangeDateIfApplicableAndIncrementLastDigit()
  if !match(getline(1,"$"),strftime("%Y%m%d")) >= 0
    %s/\d\{10}/\=strftime("%Y%m%d00")/
  else
    %s/\d\{10}/\=submatch(0)+1
  endif
endfunction

autocmd BufWritePre /tmp/test call ChangeDateIfApplicableAndIncrementLastDigit()