some Linux shell commands

Posted 2020-06-21

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 have been 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 well 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)

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