To rename multiple files using the command line, you can use the rename command or a shell script. Its syntax is as follows.
$ rename regular_expression files
As you can see, the catch is that you need to know regular expressions. But for simpler tasks, regular expressions are really easy. For example,
$ rename *.htm *.html
This changes the extension of all files from .htm to .html.
$ rename "s/ *//g" *.jpg
This code removes spaces from filenames. Rename functions can be used for more powerful renaming features but the limitation is what you can do with a regular expression. For more powerful features, you need to write a shell script. The following shell script renames all photos in a folder to rockies-100.jpg, rockies-101.jpg, ...
i=100 for j in *.jpg; do mv "$j" "rockies-$i.jpg" ;(( i++ )); done
A note about shell scripts. Do not add additional space i = 1 is not the same as i=1