Is there a jpg file resizing program that can be run from thje command line so that I can write a batch file to resize many files?

i.e. works something like:

resize -50 myBig.jpg mySmall.jpg


where -50 is percentage
myBig.jpg is input file
mySmall.jpg is resized output file.

I do not want to open each file, resize, save to new file etc. as that isfar too slow.

You could use something like http://www.rw-designer.com/picture-resize

but it doesn't do percentages just a fixed output size.

or

http://www.1000files.com/Multimedia_and_Design/Image_Conversion/Batch_Image_Commander_19485_Review.html

Paint Shop Pro
Will do all but rename.
But will save the resized files to a different directory

Pixresiszer does exactly that

ACDSee will do it but it's not free ... ever heard of torrents

It's a file viewer, I've used it for years, comes with an editor and can batch convert/rename amongst other things.

Yes,

ImageMagick - http://www.imagemagick.org/

It's free and the command line syntax is almost exactly as you wrote it.