The df command reports on the space left on the file system. For example:
% df .
The du command outputs the number of kilobytes used by each subdirectory. Useful if you have gone over quota and you want to find out which directory has the most files. In your home-directory, type
% du
These compress a file. gzip is older, while xz compresses better. For example, to zip science.txt, type
% gzip science.txt
This will zip the file and place it in a file called science.txt.gz
To unzip the file, use the gunzip command.
% gunzip science.txt.gz
Similarly, you can use:
% xz science.txt
And:
% xz -d science.txt.xz
file classifies the named files according to the type of data they contain, for example ascii (text), pictures, compressed data, etc.. To report on all files in your home directory, type
% file *