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tar --help

Create Archive Of Specific Files

tar -vfcz outputfilename.gz inputfile1 inputfile2

Zipping Files And Directories

Use this to move to the directory containing the files and / or directories you want to zip

cd projects/myfolder

Zip 1 File

tar -vczf zip_output_filename.gz file_to_zip.a

Zip 2 Files

tar -vczf zip_output_filename.gz file_to_zip1.a file_to_zip2.a

Zip A File & 2 Directories

tar -vczf zip_output_filename.gz file_to_zip1.a directory_to_zip1 directory_to_zip2

"-vczf" are the options being used for the compress.

​Unziping

tar zxvf zip_filename.gz

"zxvf" are the options being used and will cause an overwrite if any files already exist

Note that if a file was set as executable when zipped this permission will remain when it is unzipped whether overwriting an existing file or not.

Unzipping From Dropbox

See here.