Get the number of files

ls . | wc -l
ls /foo/*.imgs | wc -l

Get the disk size of folder

du -hs ./datasets

Create and delete files

touch foo.txt
mkdir a_folder
rm foo.txt
rm -r a_folder

Compression

Compress and Uncompress:

tar -cvzf a_folder.tar.gz a_folder
tar -xvzf a_folder.tar.gz  # uncompression

Split and Concat:

split -b 1024m -d --verbose a_folder.tar.gz a_folder.tar.gz.part_
cat a_folder.tar.gz.part_* > a_folder.tar.gz

-b: split file by size. (use -n to split by number) -d: use numeric suffixes starting at 0, not alphabetic;

Copy huge amount of files

rsync -ahW --no-i-r --info=progress2 source destination

-a: keep file information, including owners, permissions, etc.
-h: make output human-readable.
-W: copy files whole (w/o delta-xfer algorithm), faster. --no-i-r: scan files before copying, rather than at the same time. Faster when lots of files.
--info=progress2: display a progress bar.
--dry-run: perform a trial run that doesn’t make any changes (and produces mostly the same output as a real run).
source and destination: the source file/folder and destination folder.
source/: If a trailing slash added, the content in source will be copied into the destination. So if destination doesn't exist or is empty, this works like a combination of copy and rename.