unpaper: error: no input or output files given.

The workaround is to give up the --overwrite option, create a temp file, and copy it back over the source:

$ unpaper -t pbm raw_pg-000_im_th35.pbm raw_pg-000_unpapered.pbm && mv -v raw_pg-000_unpapered.pbm raw_pg-000_im_th35.pbm
Processing sheet #1: raw_pg-000_im_th35.pbm -> raw_pg-000_unpapered.pbm
[image2 @ 0x5561ee6a2ae0] Using AVStream.codec to pass codec parameters to muxers is deprecated, use AVStream.codecpar instead.
[image2 @ 0x5561ee6a2ae0] Encoder did not produce proper pts, making some up.
'raw_pg-000_unpapered.pbm' -> 'raw_pg-000_im_th35.pbm'

I probably should have mentioned --overwrite in the subject of this report.. can't change it now.

yikes, a destructive manifestation of the same bug:

If a list of files is given with the --overwrite option, it actually clobbers one file with the output of the other.

hmm.. actually I've misunderstood the man page:

--overwrite
           Allow overwriting existing files. Otherwise the program terminates with an error if an output file to be written already exists.

I thought "overwrite" meant to overwrite the source doc, not that it was okay to overwrite the 2nd in a list. So in the end this may just be a documentation problem. I suggesting making the docs more clear. I believe this is incorrect BNF:

  unpaper [options] {input-pattern output-pattern | input-file(s) output-file(s)}

braces are invalid BNF; they should be parenthesis, and there should be angle brackets like this:

  unpaper [options] (<input pattern> <output pattern> | <input file(s)> <output file(s)>)

then the non-obvious things in angle brackets should be defined separately, like pattern. Patterns come in many forms. I tried giving '*.pgm' as a pattern and it was rejected.

Also, I suggest an "--in-place" option of sorts so users can operate directly on the source and not give an output file.