Question

Can someone please explain me how to use “>” and “|” in linux commands and convert me these three lines into one line of code please?

mysqldump --user=*** --password=*** $db --single-transaction -R > ${db}-$(date +%m-%d-%y).sql
tar -cf ${db}-$(date +%m-%d-%y).sql.tar ${db}-$(date +%m-%d-%y).sql
gzip ${db}-$(date +%m-%d-%y).sql.tar
rm ${db}-$(date +%m-%d-%y).sql (after conversion I guess this line will be useless)

Answer 1

The GNU tar program can itself do the compression normally done by gzip. You can use the -z flag to enable this. So the tar and gzip could be combined into:

tar -zcf ${db}-$(date +%m-%d-%y).sql.tar.gz ${db}-$(date +%m-%d-%y).sql

Getting tar to read from standard input for archiving is not a simple task but I would question its necessity in this particular case.

The intent of tar is to be able to package up a multitude of files into a single archive file but, since it’s only one file you’re processing (the output stream from mysqldump), you don’t need to tar it up, you can just pipe it straight into gzip itself:

mysqldump blah blah | gzip > ${db}-$(date +%m-%d-%y).sql.gz

That’s because gzip will compress standard input to standard output if you don’t give it any file names.

This removes the need for any (possibly very large) temporary files during the compression process.