1. date: show current date and time.
2. cal: calendar.
3. df: to see the current amount of free space on your disk drives.
4. free: show the amount of the free memory(if using this command at Cygwin, crocps package should be installed first).
5. exit: to end a terminal session.
6. pwd: print name of current working directory. The working directory is the current directory that we are standing in of the file system.
7. cd: change directory. Symbol "/" stands for the root directory of a file system. And the English name of the symbol is leading slash.
The directory in which most of your system's programs are installed is /usr/bin.
The symbol "."(dot) refers to the current working directory and the ".."(two dot) refers to the parent directory of current working directory.
The symbol "./" which stands for the current directory can be omitted. "./bin" is equal to "bin"
The symbol "~" refers to your home directory.
"$ cd" changes to your home directory.
"$ cd -" changes to the previous directory.
"$ cd ~user_name" changes to the user_name's home directory.
BTW: Linux supports space character in a file name. But it's not recommended to do that.(the discussion about that)
8. ls: list directory contents.
-l option list more info of files.
There are some more options that can be found on the help page.
If the prefix of a file is a period, it means that the file is hidden. So it will not be listed. Except appending -a(--all) option to ls.
-d option list the info of the directory itself instead of its contents.
--color colorize the file names. You can redefine ls to ls --color in /home/your_name/.bashrc to make the option always setted.(a post about this)
9. file: to determine a file type.
10. less: to display the content of a file. The name "less" is from "less is more". And "more" is a old pager command that does the similar thing as "less".
To enable the color control characters in the file, add -r option to less.
11. cp: copy files and directories.
12. mv: move or rename files and directories.
13. mkdir: create directories.
eg: mkdir dir1...
when the argument of a command is followed by three periods, that means the argument can be repeated. As mkdir dir1 dir2 dir3.
14. rm: remove files and directories.
-r or -R recursively rm directory and its contents.
-d or --dir remove empty directory.
-f or --force never prompt.
gvfs-trash: to move file to the trash rather than delete it like rm does. Just have tried in Ubuntu.
15. ln: create hard and symbolic links.
