Parameter Substitution

That is a bloody boring title for a blog post. AAAAAnyway, it means that when you are farting around with variables holding filenames in bash scripts, or single commands, you may want to edit the file name. For instance, remember in the PDF compression script we strip the file extension off the filename and add .pdf to create the output filename. Very useful.

This post was prompted by trying to compress a 1000+ page pdf document. The pain was that the pdfimage command only switches to 4 digit file names at 1000. So for 1-999 you get 001 etc instead of 0001. This has the potential to screw everything up when you come to compile your final pdf. You do not want page 1000 to be before page 200, just because it starts with a lower number.

So how do we insert the missing 0?

for file in imageroot-???.*; do mv $file  imageroot-0${file#imageroot-}; echo $file; done