"At least one output file must be specified" error when using concat protocol

Question

I've been attempting to concatenate all the .aac files in a directory to make one output .aac. Here is the command I'm using:

ffmpeg -i concat:1.aac|2.aac|3.aac -c copy output.aac

When I try to execute this command in the directory, I get this error:

At least one output file must be specified

I have no idea where I went wrong, but any guidance is appreciated.

Answer 1

Add quotes:

ffmpeg -i "concat:1.aac|2.aac|3.aac" -c copy output.aac