Understanding Linux commands
Instructions entered at the command line are called commands. Some commands that you enter at the command line are programs located on your hard drive. Some commands cause an automatic response from the shell; these are called built-in commands. Commands that are not built in to the shell, require the shell to search for a program with the same command name and then execute it. The shell returns an error message if it cannot find the specified command or program.
Corel LINUX commands are case-sensitive. Most commands use lowercase letters. At the command line, make sure that you use the appropriate case for commands and file and directory names. For example, if you try to list the contents of a directory by typing LS instead of ls, the shell returns the error message LS: command not found.
Linux commands are structured so that you can obtain either general or specific results. You can modify basic commands by applying options and arguments to the command line text.
For example, you can obtain a general list of all the files and subdirectories in your current directory using the List command (ls).
Mabel:~$ ls
autosave Desktop test1.txt draw2.jpg test2.txt test3.txt file1 draw1.jpg
Some commands have command options which let you add more specific instructions to the command. Command syntax usually requires a hyphen sign (-) preceding the command option to indicate that the option is activated. You can use multiple options with the same command. For example, instead of only listing the files and subdirectories as above, you can add multiple options to list the content of your current directory, marking subdirectories with a slash (/), and sorting all files by their file extension.
Mabel:~$ ls -pX
autosave/ Desktop/ file1 draw1.jpg draw2.jpg test1.txt test2.txt test3.txt
Arguments are specific to the command. You can use command arguments, such as filenames or directories, in combination with command options. For example, you can run the List command with the options used above and specify the Desktop/ directory as the command argument. The result lists the content of the desktop directory, marking subdirectories with a slash (/), and sorting files in this directory by their file extension.
Mabel:~$ ls -pX Desktop
Templates/ Trash/ MyHome.kdelnk