gzip, gunzip, zcat

What it does

How to write it

gzip [OPTION]... [FILE]...
gunzip [OPTION]... [FILE]...
zcat [OPTION]... [FILE]...

Most used

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$ run as a normal user# run as root (or with sudo)

1. 1Compress a file

   $gzip access.log
   $ls access.log*
   access.log.gz

   The original is replaced by the .gz file.

2. 2Decompress

   $gunzip access.log.gz

   Same as gzip -d access.log.gz.

3. 3Keep the original

   $gzip -k database.sql

   You get database.sql and database.sql.gz.

4. 4Read a compressed log without unpacking

   $zcat /var/log/messages-20261018.gz | tail

   No temporary file, no extra space used.

5. 5Search in compressed logs

   $zgrep -i "failed password" /var/log/secure-*.gz

   Searches old rotated logs directly.

6. 6See the compression ratio

   $gzip -l backup.tar.gz

   Shows compressed size, original size and ratio.

7. 7Test a file after a transfer

   $gzip -t backup.sql.gz && echo OK

   Finds broken downloads or cut transfers.

8. 8Compress a database dump on the fly

   $pg_dump appdb | gzip -9 > appdb-$(date +%F).sql.gz

   The dump never touches the disk uncompressed.

9. 9Restore a compressed dump directly

   $gunzip -c appdb-2026-10-25.sql.gz | psql appdb

   -c writes to stdout, the file stays.

10. 10Compress all old files in a folder

    $find /srv/exports -name "*.csv" -mtime +7 -exec gzip {} \;

    Saves space for data you rarely read.

11. 11Compress every file in a tree

    $gzip -r /tmp/old-reports/

    Each file is compressed alone; folders stay.

12. 12Faster compression with all CPU cores

    $tar -cf - /data | pigz > data.tar.gz

    pigz is a parallel gzip; the output works with normal gunzip.

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