gzip
Transfer and archivesPackage: gzip
Compresses a file, replacing it with its .gz version. gzip -k keeps the original; without it, it disappears, which surprises the first time on a log still open.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
gzip -t- Checks the archive’s integrity without decompressing it.
gzip -l- Reports compressed and uncompressed size without extracting.