nl:tldr:a5471

The command "nl -t ${filename}" is used to display a file with each line numbered. Here is a breakdown of the command:

• "nl" is the command itself, which is used to number lines in a file. It treats standard input or specified files as input and adds line numbers before each line.
• "-t" is an option used with the "nl" command. It specifies the format of the line numbering.
• "${filename}" is a placeholder for the name of the file you want to display with line numbers. You would replace "${filename}" with the actual filename.

So, when you execute the command "nl -t ${filename}", it will print the contents of the specified file with line numbers, using the specified format for the line numbering.