#62 'pngcrush infile outfile' may overwrite file without prompting.


I'm forwarding this bug report verbatim from http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=411033 as I think A. Costa has explained it better than I could have:

I had the bad luck to run 'pngcrush' in a
directory with only two files:

% ls -log
total 32554
-rw-r----- 1 16638693 Jun 14  2005 Jettaradio0001.png
-rw-r----- 1 16562597 Jun 14  2005 Jettaradio0002.png
% pngcrush *
   Recompressing Jettaradio0001.png
   Best pngcrush method = 9 (fm 5 zl 2 zs 2) for Jettaradio0002.png

If the above isn't completely clear, 'pngcrush' examined the first file,
then overwrote the second with an optimized compression of the first.
Result: two files with different names and the same image data, while the
original second file's image data was deleted.

It would be better if 'pngcrush', when commanded to overwrite a file,
did either of two things:

1) Prompt the user: "are you sure you want to erase fubar.png?"

2) Quit, with an error message: "warning output file exists",
   and a "--force" switch could override that.


  • Glenn Randers-Pehrson

    It's not unusual for commands to overwrite the destination file if it already exists, e.g., "cp a b" will wipe out an existing "b" with a copy of "a" without a confirmation. Requiring a confirmation would be unusual.

  • Zack Weinberg

    Zack Weinberg - 2013-09-26

    I see where you're coming from, but I think the counterargument that someone is likely to do this by accident by typing pngcrush *.png in a directory containing only two .png files is stronger. (Unfortunately on Unix there's no way for the program to tell whether or not "pngcrush foo.png bar.png" is the result of a glob expansion.) It is much less likely for someone to do that with cp or mv.

  • Glenn Randers-Pehrson

    • assigned_to: Glenn Randers-Pehrson
    • Group: -->
  • Glenn Randers-Pehrson

    Changing the "Best Method..." and "Recompressing..." messages as suggested,
    fix will be in pngcrush-1.7.68.

  • Glenn Randers-Pehrson

    Fixed in pngcrush-1.7.70:

    ls *.png

    pngcrush *.png
    Recompressing IDAT chunks in logo.png
    Total length of data found in critical chunks = 66234
    Critical chunk length, method 1 (ws 15 fm 0 zl 4 zs 0) = 42084
    Critical chunk length, method 2 (ws 15 fm 1 zl 4 zs 0) > 42084
    Critical chunk length, method 3 (ws 15 fm 5 zl 4 zs 1) > 42084
    Critical chunk length, method 4 (ws 15 fm 0 zl 9 zs 1) = 37549
    Critical chunk length, method 7 (ws 15 fm 0 zl 9 zs 0) = 36617
    Best pngcrush method = 7 (ws 15 fm 0 zl 9 zs 0) = 36617
    for output to rose.png
    (44.72% critical chunk reduction)
    (44.72% filesize reduction)

  • Glenn Randers-Pehrson

    • labels: --> FIXED
    • status: open --> closed

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