What command can be used to compress a file using gzip?

The command used to compress a file using gzip is indeed "gzip". This utility is specifically designed for compressing and decompressing files using the GNU zip format. When you run the command followed by a file name, it creates a compressed version of that file with a ".gz" extension. For example, executing "gzip filename" will produce "filename.gz", effectively reducing the file size and helping in efficient storage and quicker transfer times.

The other commands listed have different purposes or file formats. "compress" is a legacy compression command that uses a different algorithm and creates files with a ".Z" extension. "zip" is a separate compression and file archiving tool that combines multiple files into a single compressed file with a ".zip" extension, but it does not use gzip format. Lastly, "tar" is primarily used for archiving multiple files and directories into a single file, but while it can be used in conjunction with gzip (as in "tar -czf"), by itself it does not compress files in the gzip format.