Often you might find you have a folder containing hundreds of files, and you want to rename them all, for example to create a numbered list. In the Finder this would take ages, but luckily you can use the Automator app that comes free with every make to save yourself time and effort.

Start by opening up the Automator app (in the Applications folder) and create a new workflow. Add the following actions by dragging them from the list on the left. First add “Get Specified Finder Items” followed by “Sort Finder Items” followed by “Rename Finder Items”. Your workflow should look something like the screenshot below. When you add the “Rename Finder Items” action, you will be asked if you want to create a copy of the files. Generally you won't want to do this, so click the "Don't Add” button.

Also, once added, the name of the “Rename Finder Items” action will change to “Add Date or Time to Finder Items” - don’t worry, this is normal. This is just the default setting, which you can change by choosing a different option from the first drop-down menu inside the action.

What the workflow does is pretty straightforward. When you click Run in the top right, it gets the files you have added to the list in the first action. You can add the files by clicking the Add button below the list before you run the workflow. The second action then sorts the files by name, size, kind, or whatever you specify. The final action takes this list of files and modifies their file names.

There are a huge amount of options in the “Rename Finder Items” action. The first drop-down menu allows you to choose between adding a date or time, adding text, changing uppercase/lowercase, making a sequential list or performing a find and replace for a string of text.

The second action, “Sort Finder Items” is really optional and only makes a difference if you have the renaming action set to “Make Sequential”. This takes the list in the order it is given and places sequential numbers before or after the file names depending on the files position in the list.

There are a couple of alternative actions that you can use instead of the first “Get Specified Finder Items”. One option is to use “Get Selected Finder Items” instead, which will perform the renaming on whatever files you currently have selected is in the Finder. Another is “Ask for Finder Items”, which will open up a dialog prompting you to choose the files each time you run the workflow. This is a good choice if you want to regularly perform the same renaming on different batches of files. You can then save the workflow as an application (File, Save As... and then choose Application from the File Format menu) that simply runs the workflow when you open it. This gives you a shortcut so you don’t have to open up Automator every time.