most important linux commands

Here is the list of most important linux commands and easy description of the linux commands.It will provide you the great capability to access the linux operating system by by using applications on terminal using commands.

1. alias

   It provides an alias name to a command using a variable
   eg:
   • root@kali:~# alias shift=cd  /Desktop
   
   
   • shift
   
   
   • root@kali:~/Desktop#


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2. apropos

   It provides proper description of manual pages.
   It is provided a keyword and it describes that keyword completely
   eg:
   • root@kali:~# apropos mkdir
   
   in the terminal it'll describe mkdir completely

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3. apt-get

   It is the command line tool which first searches
   package and then installs it
   eg:
   • root@kali:~# apt-get install python
   
   
   • It will install python in linux

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4. aptitude

   It is the command line tool which also first searches
   package and then installs it
   eg:
   • root@kali:~# aptitude install python
   
   
   • It will install python in linux

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5. aspell

   It is an interactive tool which also first scans the files
   and if any spelling mistakes found,it helps to correct the spelling
   Syntax: aspell [options] command
   eg:
   • root@kali:~# aspell check --sug-mode=fast -d en_US imtheking.txt
   
   
   • It will check the file imtheking.txt by using fast suggestion mode and the American English dictionary

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6. awk

   It is used to parse and manipulate tabular data. It operates on a line-by-line basis and iterates through the entire file.
   
   • The basic format of an awk command is:
     awk  '/search_pattern/  { action_to_take_on_matches}'   file_to_parse

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7. bzip2

   It is used to both compress or decompress the specified file name
   
   • To compress any file say iamtheking.txt the command is
   • root@kali:~/Desktop#  bzip2 iamtheking.txt
   • the file will be converted to iamtheking.txt.bz2
   • To decompress the same file the command is
   • root@kali:~/Desktop#  bzip2 -d iamtheking.txt.bz2
   • the file will be converted to iamtheking.txt again

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8. bg

   It is the command to control the jobs.
   It is used to again resume suspended jobs by sending them to run in background
   
   • Syntax: bg [job]
   Example: bg %6
   • It will send the process with PID 6 to the background

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9. break

   It is the shell function which is use to escape from the loops
   like for,foreach,while or until loop
   • example  for sandy in 1 2 3 4 5 6 8 9
     do
     echo -n "$sandy"
     if [ "$sandy" -eq 5 ]
     then
     break #This line will break us out of the for loop

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10. basename

    It is use to disammble directory names and suffix from file names
    • for a file named magic in directory apache2, the command is:
    • root@kali:~# basename  /etc/apache2/magic
    • magic

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11. cat

    It does two things:
    • copies standard input to standard output
    • concatenates files into bigger ones
    Examples:
    • root@kali:~/Desktop# cat iamtheking.txt
    • It will display the contents of file iamtheking.txt on the terminal screen
    • root@kali:~/Desktop# cat iamtheking.txt iaminfinity.txt
    • It will copy all contents of file iamtheking.txt to iaminfinity.txt

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12. cd

    It is the linux command mainly used to change directories
    Example
    • root@kali:~# cd /Desktop
    • root@kali:~/Desktop#  
    • to go to home directory
    • root@kali:~# cd ~
    • to go to parent directory
    • root@kali:~# cd ..
    • to go to previous directory
    • root@kali:~# cd -

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13. cp

    It is use to copy file(s) or directory to another file or directory
    example
    • root@kali:~# cp iamtheking.txt iaminfinity.txt
    • contents of iamtheking.txt is copied to iaminfinity.txt
    • root@kali:~# cp iaminfinity.txt dircommand
    • file iaminfinity.txt is copied to directory dircommand

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14. clear

    It clears the full terminal screan

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15. chmod

    It stands for change mode and it is used to change the permission bits of the given file
    example
    • let i have file named iamtheking.txt and i want it like
    • others can only read my file
    • group members can read & execute my file
    • and the user can read, write and execute the file
    • chmod g=rx,u=rwx,o=r iamtheking.txt
    • Here u means user , g means group and o means other

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16. cal

    It is used to display calender on the terminal screen
    Examples
    • cal -y
    • desplays the current year
    • cal -m anymonth
    • displays the month of the year written at the place of variable anymonth

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17. cmp

    It is the linux command used to compare two files of any directory byte by byte
    If the two files are differ, then it will specify the byte and the line number where they are different
    Example
    • root@kali:~/Desktop#  cmp iamtheking.txt iaminfinity.txt
    • iamtheking.txt  iaminfinity.txt differ: byte 10, line 1
    • root@kali:~/Desktop#  cmp  -b  iamtheking.txt  iaminfinity.txt
    iamtheking.txt  iaminfinity.txt  differ:  byte 10, line 1 is 153 k 151 i
    

    Here -b is used to display the bytes that are different from each other

    • root@kali:~/Desktop# cmp -l iamtheking.txt iaminfinity.txt
    • 10 153 151
      11 151 156
      12 156 146
      13 147 151
      cmp: EOF on iamtheking.tx
      

      Here -l is used to output the differing bytes numbers and their values

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18. comm

    It is the linux command used to compare two sorted files on a line by line basis
    • Examples
    • comm  iamtheking.txt  iaminfinity.txt
    • sorted files iamtheking.txt and iaminfinity.txt will be compared line by line
    • With no options, produce three-column output. Column one contains lines unique to iamtheking.txt, column two contains lines unique to iaminfinity.txt, and column three contains lines common to both files.
    • we can also use options
      -1 suppress column 1 (lines unique to FILE1)
      -2 suppress column 2 (lines unique to FILE2)
      -3 suppress column 3 (lines that appear in both files)
      for eg,
      comm -1 -2 iamtheking.txt iaminfinity.txt
      it will display lines common to both files.

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19. curl

    It is a tool to transfer data from or to a server, using one of the supported protocols (DICT, FILE, FTP, FTPS, GOPHER, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3, POP3S, RTMP, RTSP, SCP, SFTP, SMTP, SMTPS, TELNET and TFTP). The command is designed to work without user inter‐ action.
    
    • To recover a webpage and display it on the command prompt
    • curl http://hackingbylinux.blogspot.com
    • To show header info also, the command is
    • curl http://hackingbylinux.blogspot.com  -i