Basic Linux Commands

• Inside the linux terminal:-
  • the $ represents the normal user
  • the # represents the root or admin user

• To check the hostname we can use the hostname command For Eg:-

    ```
    Input: hostname
    Output: {returns the hostname}
    ```
  

• To check the current logged in user we can use the whoami command For Eg:-

    ```
    Input: whoami
    Output: {returns the current logged in user}
    ```
  

• To check the IP on Linux we can use the ip addr command

  IP address is an unique address that identifies a device on the internet or a local network

  For Eg:-

    ```
    Input: ip addr   
    Output: {returns the ip address} 
    ```
  

• To print out the working directory we can use the pwd command For Eg:-

    ```
    Input: pwd
    Output: {prints the working directory}
    ```
  

• To make a folder on linux we can use the mkdir command For Eg:-

    ```
    Input: mkdir {directory_name}
    ```
  

• To change location or to move to another directory we can use the cd command For Eg:-

    ```
    Input: cd {directory_name}
    ```
  

• To move back to another directory we can use the cd command For Eg:-

    ```
    Input: cd ..
    ```
  

  Here, the .. means that we should move one step back.

• To clear the screen we use the clear command For Eg:-

    ```
    Input: clear
    ```
  

• To search for our folder/file inside a specific location we can use the findcommand

  • To search for folder For Eg:-

      ```
      Input: find path -name {folder/directory name}
      ```
    

  • To search for file For Eg:-

      ```
      Input: find . -type f -name {filename}
      ```
    

  We can also use the locate command for finding files or folders

• To create a file we can use the touch command For Eg:-

    ```
    Input: touch {file_name}
    ```
  

• Removing a directory

  • To remove or delete a directory we can use the rmdir command For Eg:-

      Input: rmdir {directory_name}
    

  • To remove the directory and all the other files inside of it. For Eg:-

      Input: rm -r {directory_name}
    

• To view more information about the files we can use the ls -ltr command For Eg:-

    Input: ls -ltr
  

  Here, the -l means we use a long listing format. -t means we sort by time, newest first, and -r means in the reverse order while sorting.

  

• To view more information about the command we can use either the man command or the --help arguement For Eg:-

    Input: ls --help 
            OR
    Input: man ls
  

• To edit or write into a file we can use the vi editor. For Eg:-

    Input: vi {file_name} 
  

  To start editing we need to go to insert mode for which we must press i key. Then we can insert the text as we like. To escape from the insert mode we can press the escape key. Now, to save the file, we can press :wq where wq means save and quit.

• To print the file content into the shell we use cat command. For Eg:-

    Input: cat {file_name}
  

• To count the no.of words and lines we use the wc command.

  • To count only the no of lines we use wc -l For Eg:-

      Input: wc -l {file_name}
    

• To compare two files we use the diff command. For Eg:-

    ```
    Input: diff {file_1} {file_2}
    ```
  

• To compree and decompress files We use the tar do to the packaging of files. For Eg:-

    ```
    Input: tar {options} {tar_file_name} {file_1} {file_2}
    Eg: tar cvf files.tar file1 file2
    Output: files.tar
    ```   Now, we need to compress the files.tar using the `gzip` command    For Eg:-
  
    ```
    Input: gzip {tar_file}
    Eg:- gzip files.tar
    Output:  files.tar.gz
    ```
  

  Now, to decompress the compresseed file we use the gunzip command For Eg:-

    ```
    Input: gunzip {zipped_file}
    Eg:- gunzip gzip files.tar.gz
    Output: files.tar
    ```   And lastly, we need to untar the tar files   For Eg:-
  
    ```
    Input tar xvf {tar_file}
    Eg:- tar xvf files.tar
    Output: file1, file2s
    ```
  

• To copy file rom one folder to another we use the cp command. For Eg:-

    Input: cp {source_file} {destination_path}
    Eg:- cp files.tar.gz  folder1/
  

• To rename a file we use the mv command For Eg:-

    ```
    Input: mv {old_file_name} {new_file_name}
    ```
    Here, what we do is move the contents of the old file to the new file with a new name and then delete the old file. In linux, we use such indirect renaming of a file. 
  

• To split and combine the files

  • To combine a file For Eg:- Let’s suppose we want to create a new file- filec with the contents of two different files: filea and fileb. To do this we use the > operator. For Example:-

          ```
          Input: cat filea fileb > filec
          ```
    

  • To split a file For Eg:- Let’s suppose we want to split the content of a filea into two files fileb and filec then we use the split command. For Example:-

      ```
      Input: split -l 1 filea
      ```
    

• To search for words in a file and show them in a console we use the grep command For Example:-

    Input cat {file_name} | grep {word}
  

  Here, the | is the pipe operator which is used to chain the operations. Here, the ‘cat {file_name}’ returns some output, and its output is sent as an input to the ‘grep {word}` command.

• To read the start and end of the files we use the head and tail command respectively For Example:-

    ```
    Input: head -2 {filename}
    Output: prints the first two line from the file. 
    Input: tail -2 {filename}
    Output: prints the last two line from the file.
    ```
  

• To sort the file we use the sort command For Example:-

    Input: sort {file_name}
  

• To prin only the unique value we use the uniq command For Example:-

    Input: sort {file_name} | uniq