8mo ago

Can you grep through ebooks?

I was trying to do that but I noticed ls | grep searchterm just searches the book TITLES for searchterm. Is this possible, to search the text of ebooks?

16 comments

Try ripgrep-all.
- This looks pretty cool, thanks!
  
  Glad to help!
ls lists files, if you pipe it to grep it will print matching lines with file names. Universally you can't grep through ebook content, but you can do it with epub, probably other zipped text formats using zipgrep or just unzipthem and grep unarchived files.
- Thanks!
Yeah, that's to be expected with ls as it only lists the folder contents. Which format do you have?
- epub, mobi and pdf
grep searchTerm file
- You can't grep zip archives directly.
  
  Ripgrep-all has that capability.
Sounds like a good time to mention that "Little Brother" by Cory Doctorow is available in GNU Info format (usually used for manpages).
It's going to be different for different file formats. For example, something like epub is going to be hard because the format is really just a zip file with a specific internal file structure. So, it's not really the .epub file you want to grep, but one of the files within that zip file you want to grep through. EBooks stored as PDFs could be a bit easier, as they are a monolithic file format with text often (though not always) stored just as plain text. However, the text streams can be encrypted and/or compressed (FlateDecode); so, there is no guarantee of seeing plain text.
I'm sure there are more formats, but I think you get the idea, how you would do a string search comes down to the actual file format. And some are not going to be easily greppable. It's not impossible, just not straight forward.
- For example, something like epub is going to be hard because the format is really just a zip file with a specific internal file structure. So, it's not really the .epub file you want to grep, but one of the files within that zip file you want to grep through.
  ePub is a zip file contains a batch of HTML file for contents and some XML files for metadata. So you can extract it and do grep as you do for HTML files.
  
  That was just the first example to pop to mind where you couldn't just grep search * and I didn't want to get into a bunch of specific file formats. For something like epub you could probably just use zcat and then pipe the output to grep. Perhaps using a for loop if you want to do other fancy stuff along the way (e.g. output file names as headers).
  So ya, "hard" may have been a bit overblown. "not simple" may have been better. But, without the OP actually stating what format the ebooks were in, I wasn't going to write a primer on dealing with any format.

16 comments