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Basic Commands in Linux


									Linux Workshop
            Session 1
     Khadka, Santosh and Panthi, Sanjeeb
          Computer Science Department
                       Lamar University
       What is covered?

Working with files
 Working with directories
 Some basic commands
 Process related commands
 Working with vi editor
 Brief Introduction to Nano Editor
   Galaxy Account can be used to access all the Linux
    machines in the lab 208, both locally and remotely
• To access locally, go to the any machines in 208 and use your
  username and password to login.
• To access remotely, use any secure shell (ssh) software.
  Example puTTY .
• Open a terminal by right clicking on your desktop.
• Type pwd -> shows the current working directory. You are in
  your home directory.
      Tools Required for Remote Access
• ssh client
     - Example: putty for Windows platform

• sftp client
     - Example: WinScp for Windows platform

• remote sftp compatible editor
    - Example: jEdit for platform that supports java
                  Working with files
• To list all the files and/or folders in a current directory by
  ls [option]… [file]…
• Options:
   • -a: to list all files
   • -l: to list in long format showing file attributes and
   • --author : gives the author name of the files. Better use
      with the combination of –l.
• File: Default is current working directory.
                 Working with files
• vi <filename> -opens a file to edit if exist, otherwise creates
                      new file to edit
• ls      - lists contents in current directory
• ls /etc - lists contents in directory /etc
• ls -a - this will list all file including those beginning with
            the'.' that would normally be hidden from view.
• Output redirection - Copies the output to some other file.
  Example: ls –l > filename (overwritten)‫‏‬
               ls –l >> filename (appended)‫‏‬
                    Working with files
• ls -l   - this gives a long listing showing file attributes and file
  drwxrwxr-x 6 santoshk santoshk 4096 Sep 14 11:39 test
  -rw-rw-r-- 1 santoshk santoshk 140 Nov 17 09:08 test1.c
• cat <filename>
   - displays the content of the file
   - example: cat filename
   - cat –n filename (-n option for giving the line number)d
• cp <sourcefile> <destinationfile>
   - copy the content of the file
   - example: cp sourcefile.txt destnationfile.txt (source file is
      not deleted/modified)‫‏‬
                   Working with files
• script
        - to make script file
        - records everything printed on your screen. The record is
          recorded to the filename specified.
        - starts scripting, once done, type in <ctrl>+d to end
  script filename - makes a script file with the given filename
  script -a filename - append the session record to filename,
                         rather than overwrite it
• mv <sourcefile> <destinationfile>
   - example: mv sourcefile.txt destiantionfile.txt (the sourcefile
      file is deleted)‫‏‬
                    Working with files
• tar - create archives and add or extract files
• tar –cvf output.tar inputfile
  Example: tar –cvf aos.tar AOS
• restore a tar file
   - tar -xvf inputfile.tar
   - .tar file is not compressed by itself. It just bundles the list of
      files in one folder.
   - add -z option to create a compressed tar file

    Example: tar -cvzf file.tar.gz
                  Working with files
.gzip – compress the files

           gzip <filename>
.gunzip –decompress the file
           gunzip <filename.gz>
                 Working with files
• wc     - counts the number of lines,words and bytes in the file
         - example: wc –l filename

• head - outputs the first part of the file
       - prints the first 10 lines by default
       - example: head filename
                    head -n count filename

• tail - outputs the last part of the file.
       - example: tail mylist.cpp
                 Working with files
• lpr - print command
       - command: lpr -p printername filename
   Example: lpr -p lab208Printer -#2 file1.txt file2.txt
            (this will print two copies of file1.txt and file2.txt)‫‏‬

   Note: This is not available at present.
            Working with directories
• cd - changes the directory
     - example: cd <foldername>

• mkdir - creates a directory under the current working
        - example: mkdir <foldername>

• rmdir - remove files
        - example: rmdir <directoryname> (for empty directory)‫‏‬
          rmdir –rf directoryname (recursive deletion with force)‫‏‬
            Working with files contd..
• Absolute path: start with / (root) to go specific directory
  regardless of where you are now.
• Relative path : start with the current directory to go specific
• Example:
   • If, pwd: /home/myfolder then to go /home/myfolder/c++
   • Absolute path : cd /home/myfolder/c++
   • Relative path : cd c++
           A few basic commands
• man - help manual
       - example: man keyword
       - press <Space bar> to view the next page
       - press <return> to view next line
       - type‫“‏‬q”‫‏‬exit‫‏‬
• date - display or change the date
       - example: date --date‫ 2„=‏‬days‫‏‬ago‟
              date --set=“2009-9-4 11:59”
              date '+DATE: %m/%d/%y%n TIME:%H:%M:%S'
               DATE: 02/08/01
             A few basic commands
• chmod      - used to change the access permission
              - used to set file permissions to owner, group, and
  -rw-rw-r-- 1 santoshk santoshk 140 Nov 17 09:08 test1.c
              - r = 4, w = 2, x = 1
              - example: chmod 444 mylist
• clear
             - clear the screen

• grep       - search the file for the specific text
             - example: grep string filname
             A few basic commands
• hostname - displays or set the system name
                - example: hostname [name]
                - with no arguments prints the current host name.
                - with arguments sets the current host name to the
                  specified string.
• more
               - display output one screen at a time
               - related command: less
• quota      - display disk usage and limits
             - related command: du, df
   du –estimate the file space uses
   df – disk space uses (amount of disk space available)
            Process related commands
• ps    - gives information about the running processes
        - example: ps -ef
                    ps -fu username

• kill - sends a signal to a process to kill (ends the running
       - example: kill -9 pid

• exit - exit from the shell. If there are suspended jobs one
         cannot exit from the shell , so kill the processes
         using the kill command.
           Brief Introduction to vi Editor
• vi filename
•  esc - to enter vi command mode
• h: moves the cursor one character left (l right)
• j :moves the cursor one character down (k up)
• u :undo the last changes in the file
• x :deletes the character under the cursor
• d^: deletes all the characters from current cursor to beginning of
  the line
• d$ :deletes all the characters from current cursor to end of the line
• dw: deletes one word from the cursor.
   Brief Introduction to vi Editor contd..
• Insert text
   Enter input mode and:
   i a - insert text before ('i') or after ('a') the current character
   I A - insert text at beginning ('I') or end ('A') of current line
   o O - open new blank line after ('o') or before ('O') current line
    r R - replace‫‏‬one(„r‟)‫‏‬or‫‏‬more‫‏‬character‫„(‏‬R‟)‫‏‬by‫‏‬overwriting
       Brief Introduction to vi Editor
• Exiting and Saving
    - Press esc and type
        :q to quit
        :wq or ZZ to save and quit
        :q! to quit without saving (!= Forcefully)
        :w to save the file
        :w filename to save current file under name filename

• Copy and Paste text
     nyy or nY - 'copies' n number of line
     pP        - insert the contents of the paste buffer [ after /
          before ] the current line/character.
           Brief Introduction to vi Editor
• Delete text
    x X         - Delete current ('x') or previous ('X') character
    dw          - Delete the current word
    dd                   - Delete the current line
    D           - Delete the rest of the line
    5dd         - Delete the next five lines
   37Gdd        - Delete line 37
   J            - Join lines

•   Undo
       u        - Undo most recent change to the file
         Brief Introduction to vi Editor
• Global Searching and replace:
      /text - Search forward for some <text>
      ?text - Search backward for some <text>
      n       - Repeat the previous search for the 'next' occurrence
      N       - Repeat the previous search but in the opposite
      ' ' (two single quotes) - Go back to where you where
       :1,$s/oldtext/newtext/g - global substitutions
        Brief Introduction to vi Editor
• Other popular commands
         ^      - go to start of line
         $      - go to end of line
        :1      - goes to top of file
        :5      - goes to fifth line of file
        :$      - goes to bottom of file
       :set nu - will number all your lines
       :set nonu - turn off line numbering
       Ctrl-g - show line number of current line
   Brief Introduction to Nano Editor
• To edit a file called filename, type nano filename.
• cntrl g - (^G) with display a Help file with a bunch of
                     information about using nano.
• cntrl o - (^O) or (f3) will write or save the file
• cntrl x - (^X) will exit the program and return you to the
• cntrl d - (^D) delete character currently under the cursor
• cntrl k - (^K) delete entire line
• cntrl u - (^U) paste text
• ^\      - search for (and replace) a string of characters
• BackSpace delete character currently in front of the cursor
             Compiling files in linux
• C++ file
              g++ [options] source_file –o outputfile
              g++ myfile.cpp
              g++ -Wall myfile.cpp -o outputfile

• C file
   gcc [options] source_file –o outputfile
   gcc myfile.c
• java file
              java Myfile
                 Debuggin c/c++ file
• gdb outputfile
• To set the break
   • (gdb) break filename:line number
   • (gdb) functionname
• To remove the break
   • (gdb) clear function /line number
• To run
   • (gdb) r
   • (gdb) step (each step)
   • (gdb) next [count] // how many line
               Debuggin c/c++ file
• To watch the variables
   • (gdb) watch variablename
   • (gdb) watch expression
• To quit
   • (gdb) q
Thank You !!!

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