Apple - Make existing PDF searchable ( OCR ) via command line / script
What you want is Tesseract OCR. It's an open source OCR that is maintained by Google and supports a variety of platforms. It also has a native command line interface. It's exactly what you're looking for and available from the Mac ports project as well as homebrew.
Project Home: https://github.com/tesseract-ocr
How to install on OS X: http://blog.matt-swain.com/post/26419042500/installing-tesseract-ocr-on-mac-os-x-lion
Usage Example: tesseract -l eng input.pdf output
Disclaimer: NOT AN OCR SOLUTION (but this answer is still useful to extract text from pdf)
There is an Apache Software Foundation project called Apache Tika:
A toolkit detects and extracts metadata and structured text content from various documents using existing parser libraries
They support PDF text extraction using PDFBox:
allows creation of new PDF documents, manipulation of existing documents and the ability to extract content from documents. Apache PDFBox also includes several command line utilities
And they recently also added support for OCR (via Tesserac)
For a text based solution, PDFBox makes very simple to extract text from a PDF:
- Download the
pdfbox-apppackage from https://pdfbox.apache.org/downloads.html run the
ExtractTextcommand on it:java -jar pdfbox-app-x.y.z.jar ExtractText myNiceBook.pdf myNiceBook.txt
It also has some other nice options that you can see in ExtractText docs.
It's not entirely clear to me what your requirements are for being able to "script" this from the "command line".
If you are talking about automation, then that is possible with any number of utilities.
ABBYY FineReader Express + Keyboard Maestro + Hazel
I use ABBYY FineReader Express + Keyboard Maestro + Hazel like so:
Hazel monitors a given folder for any new PDFs
if a PDF is found, it is opened in "ABBYY FineReader Express"
Keyboard Maestro then automates the process of turning the PDF into a Searchable PDF (OCR) and saves the file to a different directory.
Now, if you don't own Hazel and Keyboard Maestro already, your initial costs are going to rise pretty quickly (although I depend on both so much I consider them a bargain).
PDFPen + AppleScript + Folder Actions
You could do something similar with PDFPen (or PDFPenPro) and folder actions and AppleScript. See https://gist.github.com/prenagha/1355037 for one example.
Marco Arment did a survey of OCR apps for Mac and found that PDFPen had great results and was easy to automate.
A google search for "PDFpen applescript OCR" will turn up a number of alternatives.