[NTLUG:Discuss] shrink images globally

[Terry Henderson]

I sometimes find the need to resize a whole directory of images to a
certain size and would like to learn some efficient way to do it
globally.  I use gimp, but it's several mouse clicks and you manually
enter pixel sizes each time for each image and if there are 20 or 30
images, well, you can imagine, it's time consuming.
I'm usually wanting to make them smaller and all the same size. 
convert -size 512x348 * 
works well, but what you end up with is all of the originals
untouched, and a whole new set of resized files with new names like,
[assume we have just 4 files, p0001.jpg - p0004.jpg] p0004.jpg.0 
p0004.jpg.1 p0004.jpg.2  p0004.jpg.3  When, what I'd rather do is just
overwrite with same 'ol filenames as before.  Or just something
besides adding .1 .2 .3 etc. to end of files, like p00040.jpg
p00041.jpg p00042.jpg p00043.jpg Or just simply overwrite all and 
leave them all same filenames, but just smaller images.

I can use command:
convert -size 512x348 * +profile '*' smaller.jpg
and that just gives me:  smaller.jpg.0 smaller.jpg.1 smaller.jpg.2 smaller.jpg.3
Sounds so simple, but just don't see any way to do what I really want to do.
Am I just using the wrong application?  or?