Basics commands in Linux
The ls command
ls ----- Command is equivalent of the DOS dir command. It lists the files and subdirectories contained within the present directory.
Some possible flags which can be used with the ls command are:
ls -a List all files including hidden files which starts with.(Dot).these hidden files will not be displayed with simple ls command
ls | more Lists files and directories page after page on keystroke. The above command actually is a combination of two commands. It introduces a new concept called 'Piping'. It is done using the logical OR or | character found just above the Enter key on your keyboard. In Linux it is possible to give the output of one command to another command as an input. The ls command lists files & subdirectories and the more commands divides its input into page length views. Thus piping the ls output to more results in page length views of files and subdirectories.
ls –R It lists the files and subdirectories of a directory and further lists the contents of each subdirectory recursively. The output of this command is usually large and is best seen when piped through more.
pwd The pwd or the present working directory command gives you the path to the directory in which you presently are. It is used without flags simply as 'pwd'
su Many times you might have logged in as a normal used and might need to be root to install a software or for some other small task. You could logout then login as root complete the work logout and login back as a normal user. Instead, you can just use the su command. The format is:
su username
e.g.: su root
When you 'su' to become root from a normal user, you are asked for the root password. But if you are root, you can use 'su' to become any user without using a password. Once your work is finished, use 'exit' to become yourself.
whoami It will tell you which user you are logged in as. Useful when you have used 'su' many times and now don't know who you are.
cp This one copies files / directories from one place to another its syntax is
cp source_file_with_path destination_path
e.g.: cp /home/bala/secret.txt /ftp/pub
This would make a copy of secrets.txt from /home/bala to /ftp/pub.
cp –i Interactive copying, prompts before overwriting files or directories
cp -l source_file_with_path destination_path
Makes a link (shortcut) to the source_file at the destination path instead of actually copying it there.
cp –p Preserve file attributes while copying if possible
cp –R Copy Recursively. Used when copying directories. This command also copies the contents of the subdirectories.
cp –u Update i.e. Copy only if the source file is newer than the destination file or the destination file does not exist.
rm The rm command is used to remove or delete files or directories. Its general format is:
rm -flag file_or_directory_with_path
Eg: rm /home/bala/recycle.txt
Some flags which can be used with the rm command are
rm -v test.txt
Remove verbosely, explain what is being done.
rm -r directory
Remove the directory and its contents recursively.
mkdir This command is used to create new a new directory. Its syntax is
mkdir -optional_flag directory_name
The possible flags are
mkdir -v directory_name
Tell what is going on.
mkdir -p directory_with_path
This is a cool command. Suppose you need a directory named data within another directory called report in /usr/local and the parent directory report itself does not exist, then you can use :
mkdir -p /usr/local/report/data
This command creates the report directory and the data subdirectory in one go.
man For someone new to linux, the man command is one of the most important commands. The syntax is:
man command_name
Suppose you have not understood fully one of the above commands or want to find out about a new command you have learnt, the man command provides a manual for that command
