znew:tldr:d4b7f

This command is using the "znew" command to compress and decompress files in the ".Z" compressed format.

Here is an explanation of the individual parts of the command:

• "znew" is a utility command in Unix-like operating systems used to convert ".Z" files created by compress into ".gz" files compatible with gzip.
• "-v" is an optional flag that stands for "verbose". When used, it provides more detailed output and progress information during the execution of the command.
• "${filename1-Z}" is a variable that represents the first file name. The value of this variable is substituted in place of this expression. If the variable is not set or empty, "Z" is used as a placeholder.
• "${filename2-Z}" represents the second file name, and again, if the variable is not set or empty, "Z" is used.
• "${filename3-Z}" represents the third file name, and similarly to the previous variables, if it is not set or empty, "Z" is used.

In summary, this command is using the "znew" command to compress or decompress files that have the ".Z" extension. The verbosity flag (-v) is optional and can be used to provide more detailed output. The filenames are represented by variables, and if the variable is not set, a default value of "Z" is used.