man tar
tar --help # Shows all available params

# c = create
# z = filter the archive through gzip
# v = verbosely list files processed
# f = use the archive file or device archive

# tar -czvf <name_of_tar_gz_file> <directory_or_file_to_compress>

tar -czvf plugins.tar.gz plugins

tar --help # Shows all available params

# x = extract from the arhive
# z = filter the archive through gzip
# v = verbosely list files processed
# f = use the archive file or device archive

# tar -czvf <name_of_tar_gz_file> <directory_or_file_to_compress>
tar -czvf plugins.tar.gz plugins

man du
du --help # Shows all available params

# you may or maynot need to sudo pending the file and folder 
# permissions of the directory you are wanting to calculate

# s = summarize
# h = human readable (my favourite)

# du -sh <path>/*
du -sh ./* # will display summary of the current working directory

man rsync
rsync --help

# a = archive mode; equals -rlptgoD (no -H,-A,-X)
# v = increase verbosity
# z = compress file data during the transfer
# h = output numbers in a human-readable format
# --dry-run = simulates what would happen but does not actualy copy or sync

# local example
# rsync -avzh <source> <dest> --dry-run

# copy a file/folder from local to server over ssh
# rsync -avzh <source>/* <user>@<host>:<dest>/ --dry-run

# copy a file/folder from local to a server over ssh with a non standard port
# rsync -avzh --rsh='ssh -p2345' <source>/* user@host:<dest>/ --dry-run

rsync -avzh ./ /tmp/backups # copy files/folders from current working directory to backup directory

man free
free --help

# m = show output in mebibytes
# h = show human-readable output

free -mh # available memory

man ps
ps --help simple

ps aux  | awk '{print $6/1024 " MB\t\t" $11}'  | sort -n # memory used by what