How to incrementally rename files after processing in bash?

Question

I have a set of files that need processing, so I tend to do this programmatically in bash in mac and linux. Since I like to keep the originals in case something gets screwed, I want the files to come out renumbered incrementally, but I don't know the proper bash construction to accomplish this.

Here's an example. I have a set of .pdf files:

bulletinlois00.pdf
bulletinlois01.pdf
bulletinlois02.pdf
...
bulletinlois33.pdf

The pdfs have not yet been OCRed, and so I want to iterate through them with tesseract or ocrmypdf but instead of outputting them like bulletinlois01.pdf they would be 01.pdf. Here is another example using the same file set. I want to iterate through files doing pdftotext, but instead of having bulletinlois01.pdf go to bulletinlois01.txt I want it to be 01.txt

I could do a cp+mv process, or grep to replace the unwanted parts of the names, but this seems overkill and gets me confused about whether I should be using wait or a && construction.

Is there a simple way to script this using bash, and could you please explain what exactly the construction is doing so that I can learn how to adapt it to other, more complex processing I need to do? For instance, maybe I could use the construction to output the names using

`date "+%H.%M.%S"`

Here's the rudimentary script:

for f in *.pdf ; do
    tesseract -l fra "$f" "$f"_done.pdf
done

Answer 1

You can have more control over the resulting filenames by stripping prefix and suffix from the matched filenames.

This is one possible way to achieve that:

for matched_filename in bulletinlois*.pdf ; do

    # strip "bulletinlois" prefix from the filename
    tmp=${matched_filename#bulletinlois}

    # then strip ".pdf" suffix
    number=${tmp%\.pdf}

    tesseract -l fra "$matched_filename" "$number"_done.pdf
done

Stripping in this example is done using bash shell parameter expansion.

To find out more about shell parameter expansion visit this blog post or the official bash documentation.