sponge:tldr:fadef

This command performs a specific operation on a file using the "grep" and "sponge" commands.

Here is a breakdown of the command:

1. "grep" is a command-line utility used for searching files and filtering text based on patterns. It is used here with the "-v" option, which instructs grep to select non-matching lines.
2. "^" is a regular expression pattern that matches the start of a line.
3. "${#}" is a shell variable that represents the length of an argument passed to the command. In this case, it refers to zero-length lines.
4. "filename" is a placeholder representing the name of the file to be processed by the command. You should replace it with the actual filename you want to work with.
5. The "|" symbol is a pipe operator that redirects the output of the "grep" command to the input of the "sponge" command.
6. "sponge" is another command-line utility that soaks up standard input and writes it to a file. It is useful when you want to modify the contents of a file without using temporary files.

Overall, this command is used to remove lines that have zero length (empty lines) from a file, and the modified content is then written back to the same file.