nl:tldr:1ffad

This command is broken down into several parts:

1. cat: Short for "concatenate," it is a command in Unix-like operating systems used to read and display the contents of files.
2. ${filename}: This is a variable placeholder that should be replaced with the actual name of the file you want to display.
3. |: Known as a pipe symbol, it redirects the output of one command as input to another command.
4. nl: A command used to number lines in files or standard input.
5. ${options}: This is another variable placeholder for any additional options or flags you want to pass to the nl command.
6. -: The hyphen or dash is often used as a placeholder in commands to signify reading data from standard input.

So, when you execute this command, it will read the contents of the specified file using cat, pipe the output to nl command to add line numbers, and then display the result. The ${filename} and ${options} placeholders need to be replaced with the actual values for this command to work correctly.