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11597 :: remove first 4 lines from string

• ITwrx (orginal) [2024-05-13T22:23:09+02:00] view original

  I'm trying to use strutils.removePrefix to remove the first 4 lines from a string, but i'm having trouble matching the first four lines. I'm guessing it has something to do with the newlines. How am i supposed to make this match? thanks.

  #my code

  varChunk = chunk
  prefix = "\n" & stringChunkLineSeq[0] & "\n" & stringChunkLineSeq[1] & "\n"
  echo "--------- start prefix -----------"
  echo prefix
  echo "--------- end prefix -------------"
  echo varChunk.startsWith(prefix)
  varChunk.removePrefix(prefix)
  echo varChunk
  Run

  #my terminal output.

  --------- start prefix -----------
  
  Content-Disposition: form-data; name="file1"; filename="price_list.txt"
  Content-Type: text/plain
  
  --------- end prefix -------------
  false
  
  Content-Disposition: form-data; name="file1"; filename="price_list.txt"
  Content-Type: text/plain
  
  $25 (5th line of varChunk)
  Run

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• janAkali (orginal) [2024-05-14T08:27:09+02:00] view original

  While the text looks the same in both instances, it could have non-printable characters or terminal command chars that you can't normally see. On Linux you can use cli tools like od to inspect output in detail, e.g.:

  
  $ nim r program.nim | od -a
  0000000  nl   C   o   n   t   e   n   t   -   D   i   s   p   o   s   i
  0000020   t   i   o   n   :  sp   f   o   r   m   -   d   a   t   a   ;
  0000040  sp   n   a   m   e   =   "   f   i   l   e   1   "   ;  sp   f
  0000060   i   l   e   n   a   m   e   =   "   p   r   i   c   e   _   l
  0000100   i   s   t   .   t   x   t   "  nl   C   o   n   t   e   n   t
  0000120   -   T   y   p   e   :  sp   t   e   x   t   /   p   l   a   i
  0000140   n  nl  nl   $   2   5  sp   (   5   t   h  sp   l   i   n   e
  0000160  sp   o   f  sp   v   a   r   C   h   u   n   k   )
  Run

  Or, if you're absolutely sure input data uses 'n' for line separation, you can just count newlines and remove enough chars from beginning using strutils.delete:

  import std/strutils
  
  proc removePrefixLines(s: var string, n: Positive) =
    var ind, lines = 0
    while lines < n:
      if s[ind] == '\n': inc lines
      inc ind
    s.delete(0..ind-1)
  
  varChunk.removePrefixLines(4)
  echo varChunk
  Run

---

• Zoom (orginal) [2024-05-14T13:21:46+02:00] view original

  The code works exactly as intended: the prefix isn't getting deleted because it doesn't match. What it means is that perhaps your input is not as deterministic as you think and you need to change the strategy. For example, use std/pegs to match only the meaningful content in the start of the string and ignore the rest.

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• ITwrx (orginal) [2024-05-14T18:04:42+02:00] view original

  Thanks a lot to both of you!

  I figured my \n was probably the reason for the non-matching condition, but was not sure what \n was supposed to be. I had searched before, but didn't find the info i needed. Spurred by your confirmations, i searched again, and my code now matches the input.

  It was supposed to be:

  prefix = "\r\n" & stringChunkLineSeq[0] & "\r\n" & stringChunkLineSeq[1] & "\r\n"
  Run

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