Question: I have a few hundred files named hortstu01-01-14 then hortstu01-02-14... Do you get the idea?

Well half of the files are named hortstu\_01-03-14 then hortstu\_01-04-14.

This messes up sorting the files by name and getting them in the order I'd prefer them to be. So I'd like to rename the ones without the underscore to hortstu\_ 

Is it possible to do this in a batch operation? If so how?

Answer: 
Open a terminal. Firstly, double check you have the perl `rename`, by typing `man rename`. At the bottom, it should say `perl v5.18.2` or similar. (I think Ubuntu always ships the perl `rename`, but other distros ship other versions.)

If it's the correct version, then `cd` to the directory that contains these files. Then run

```
 rename 's/^hortstu/hortstu_/' hortstu[!_]*

```

Explanation
-----------

* This will rename all files that match `hortstu[!_]*`. This means files that start with `hortstu`, and do *not* have `_` next.
* It will then rename them by
	+ finding `^hortstu` (i.e. `hortstu` at the beginning of the string)
	+ replacing it with `hortstu_`.
* N.B. the format for `hortstu[!_]*` is a [bash glob](http://www.tldp.org/LDP/GNU-Linux-Tools-Summary/html/x11655.htm). The format for `^hortstu` is a regular expression.
For those who prefer GUI applications or just like the ability to preview the result, you might want to install Thunar. It's the main file manager of XFCE; you find it in the repositories.

When you select multiple files in Thunar and rename them (via context menu or F2), you get an elaborate dialog which support all kinds of rename operations. You can solve your problem like so:

![enter image description here](https://i.stack.imgur.com/iN737.png)