Q : How do I launch a file located inside the folder I have in focus, Without browsing into that folder?

To launch a file that is somewhere under the folder that currently is in focus you need to create a multi-script command. And then you can assign that command to a keyboard shortcut and you can run this command by just hitting a key.

Create Command

1. Open the "User Defined Command" dialog from the configuration menu.

2. Click the "New" button and name you command and select "Multi-Script" as command type.

3. Write the script. (See below)

4. Press the Save button.

5. Press the Hotkey button to open the Keyboard customization dialog

6. Under Module select " User Defined Command".

7. Select the command that you created above and Assign a shortcut key for it. For example Ctrl+P 

8. Close all dialog and now stand on the folder that has the file that you want to launch.

9. Press Ctrl+P. Now the default launch action for the file will be execute. If it is a mp3 or avi file it will be played by the default player for that file type, If it is a exe file it will start that program. It will do all this without you having to browse into the folder and launch the file yourself.
 

The Script

The file you want to launch can be anything that you normal can double click on to launch, a MP3 file , AVI File, TXT file , EXE file, and more.

If you for example want to view the the first .txt file that is found inside the folder that are in focus, Then script can look like this

@var $file
$file = _findfirstfile( "{focusfilepath}\*.txt" );
MC.Run CMD={$file} SHELL

First you need to create a variable that will store path to the txt file that we are going to look for.  Here we calls it $file.

The tag {focusfilepath} will be replace with the full path to the file or folder that are currently in focus.
_findfirstfile wants a path with a search filter. So add "\*.txt" to the path we get from the {focusfilepath}. This will tell the function to return the first file ending with ".mp3" it finds in that folder.

If a file was found the the full path to that file is now stored in $file. We now want Windows to launch that txt just like if we double clicked on it.

That is done we telling the Windows Shell to launch the file. This is done with the MC.Run command

MC.Run CMD={$file} SHELL

We need to but the $file parameter inside { } because the MC.Run command is not a script command, It is a custom command, So to transfer a script parameter to the custom command we need to enclose it with { } 

If the file you want to launch is in a subfolder of the folder you has in focus, you just enter that in the path to the _findfirstfile command

$file = _findfirstfile( "{focusfilepath}\subfolder\*.txt" );

If _findfirstfile does not find any matching file it will return an empty string. And MC.Run will never run an empty command so it is safe to send an empty string to it.

More Information

User Defined Commands

Multi-Script