How to command line rotate an image?

[joe at actionline.com]

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How can I use the 'convert' utility to rotate an image?

After searching the 'net for example syntax, the only thing I have been
able to find is: convert "-rotate90" filename.jpg ... which did not work.
I've tried a dozen other variations to no avail.  One variation I tried
was this: convert filename.jpg "-rotate90" and that created a file named
-rotate90 which I am now unable to remove. In fact, I cannot even list
this file with a leading "-", much less remove it.

I tried: ls -ltr *rotat* and get this error message response:

ls: invalid option -- e
Try `ls --help' for more information.

Good grief, what have I done? And how can I unscramble my mess?