mpg123:tldr:3c26e

This command is used to play an mp3 file using the mpg123 command-line audio player. Here's a breakdown of how it works:

1. cat: This command is used to concatenate and display the content of files. In this case, it is used to read the content of the specified file.

2. ${file-mp3}: This is a shell variable substitution. It attempts to expand the value of the file variable, and if it is not set or empty, it uses the string "mp3" as a default value.

3. |: This is the pipe symbol, which is used to redirect the output of one command as the input to another command. In this case, it takes the output of cat ${file-mp3} and passes it as input to the mpg123 command.

4. mpg123: This is a command-line audio player for playing mp3 files. It takes the mp3 data from the cat command and plays it.

In summary, this command concatenates the content of an mp3 file (specified by the variable file or using "mp3" as default) and passes it as input to the mpg123 command, which will play it as audio.