# decompress .gz file (compressed .gz file will be removed after decompression)

gzip -d sample.fastq.gz

  sample.fastq

# view the content of a .gz file, and
zcat sample.fastq.gz

# view top 20 line  - pass decompressed content via unix pipe to head command
zcat sample.fastq.gz | head -20 

# tar   decompress .tar.gz files

tar -zxvf samples.tar.gz

# unix pipe  pass decompressed file into a pipe: extract all tar archive files to standard output (option -O)
tar -zxOf samples.tar.gz | head -20   # views the first 20 lines

Compression

# compress single file gzip (original file will be removed after compression)
gzip sample.fastq
 sample.fastq.gz

# tar archive - compress complete directory
tar -zcvf samples_compressed.tar.gz /path/to/sample/directory/

# to change gzip level used in tar archive (default compression level is 6, max level is 9)

# a) providing the compression command by option -I

tar -I 'gzip -9' -cvf samples_compressed.tar.gz /path/to/sample/directory/
# b) combine tar and gzip using a unix pipe
tar cvf - /path/to/sample/directory/  | gzip -9 > samples_compressed.tar.gz

Extract single file from tar archive

# list content (all files) of a .tar.gz archive
tar -tf samples.tar.gz
sample_1.fastq
sample_2.fastq

# extract selected file from .tar.gz archive
tar -zxvf samples.tar.gz sample_1.fastq
sample_1.fastq

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see also
 → www.gzip.org