File Extension Change Shortcut

Changing the extension of a file seems like something you would do often enough to know how to do it from command line.  One annoying part of moving a file is repeating the file name a second time when all I want to do is change the extension.  A minor annoyance but an annoyance nonetheless.

I recently found that you can quickly change a file's extension with this handy shortcut:

# mv filename.{old,new}
mv code.{txt,js}

The braced syntax provides a way to quickly swap out the file extension without needing to repeat the file name.  Sweet!