Archives and Compression

Two separate ideas get bundled together so often that people mix them up: archiving (combining many files into one) and compression (shrinking the size of a file). tar does the first, gzip does the second, and together they produce the .tar.gz files you have almost certainly downloaded before.

tar: packing many files into one

The name is short for "tape archive" - it dates back to literal magnetic tape backups, which is why the flags feel a bit old-fashioned. Three flags cover most of what you need:

tar -cf site.tar site/        # create an archive from the site/ directory
tar -tf site.tar               # list what's inside, without extracting
tar -xf site.tar               # extract into the current directory

Read the letters as: create, extract, table-of-contents, and file (always followed by the archive's name).

Adding compression

tar bundles files but does not shrink them by itself. Add -z to also gzip-compress the result, which is where the familiar .tar.gz (or .tgz) extension comes from:

tar -czf site.tar.gz site/     # create AND compress in one step
tar -xzf site.tar.gz            # decompress AND extract in one step

gzip and gunzip on their own

You do not need tar to compress a single file:

gzip access.log          # replaces access.log with access.log.gz
gunzip access.log.gz     # reverses it, restoring access.log
gzip -k access.log       # -k keeps the original instead of replacing it

Try it

mkdir -p site/css
echo "<h1>hi</h1>" > site/index.html
echo "body { color: navy; }" > site/css/style.css
tar -czf site.tar.gz site
tar -tzf site.tar.gz
rm -r site
tar -xzf site.tar.gz
cat site/index.html

Everything comes back exactly as it was, even though site/ itself was deleted in between.

Further reading

• "The Linux Command Line" by William Shotts (No Starch Press) - its chapter on archiving and backup covers tar, gzip, and their relatives (bzip2, xz, zip) side by side, including when to reach for each one.
• "How Linux Works" by Brian Ward (No Starch Press) - explains what compression is actually doing to the bytes, which demystifies why some file types (already-compressed video or images) barely shrink at all.