Basic Commands in Linux

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

• Working with files
• Working with directories
• Some basic commands
• Process related commands
• Working with vi editor
• Brief Introduction to Nano Editor

3
Login!

• 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 -gt shows the current working directory.
  You are in your home directory.

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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

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Working with files

• To list all the files and/or folders in a current
  directory by default.
• ls option file
• Options
• -a to list all files
• -l to list in long format showing file
  attributes and permission
• --author gives the author name of the files.
  Better use with the combination of l.
• File Default is current working directory.

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Working with files

• vi ltfilenamegt -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 gt filename (overwritten)?
• ls l gtgt filename (appended)?

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Working with files

• ls -l - this gives a long listing showing
  file attributes and file
• permissions.
• drwxrwxr-x 6 santoshk santoshk 4096 Sep 14
  1139 test
• -rw-rw-r-- 1 santoshk santoshk 140 Nov 17
  0908 test1.c
• cat ltfilenamegt
• - displays the content of the file
• - example cat filename
• - cat n filename (-n option for giving the line
  number)d
• cp ltsourcefilegt ltdestinationfilegt
• - copy the content of the file
• - example cp sourcefile.txt destnationfile.txt
  (source file is not deleted/modified)?

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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 ltctrlgtd to end
• scripting
• Example
• script filename - makes a script file
  with the given filename
• script -a filename - append the session
  record to filename,
• rather than
  overwrite it
• mv ltsourcefilegt ltdestinationfilegt
• - example mv sourcefile.txt destiantionfile.txt
  (the sourcefile file is deleted)?

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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

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Working with files
.gzip compress the files Example
gzip ltfilenamegt .gunzip decompress the
file Example gunzip ltfilename.gzgt
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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

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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.

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Working with directories

• cd - changes the directory
• - example cd ltfoldernamegt
• mkdir - creates a directory under the current
  working
• directory.
• - example mkdir ltfoldernamegt
• rmdir - remove files
• - example rmdir ltdirectorynamegt
  (for empty directory)?
• rmdir rf directoryname (recursive
  deletion with force)?

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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 directory.
• Example
• If, pwd /home/myfolder then to go
  /home/myfolder/c
• Absolute path cd /home/myfolder/c
• Relative path cd c

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A few basic commands

• man - help manual
• - example man keyword
• - press ltSpace bargt to view the next page
• - press ltreturngt to view next line
• - type q exit
• date - display or change the date
• - example date --date 2 days ago
• date --set2009-9-4 1159
• date 'DATE m/d/yn TIMEHMS'
• DATE
  02/08/01
  TIME164455

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A few basic commands

• chmod - used to change the access permission
  
• - used to set file
  permissions to owner, group, and other
• -rw-rw-r-- 1 santoshk santoshk 140 Nov 17
  0908 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

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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)

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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 process)
• - 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.

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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.

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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 - replace one(r) or more character
  (R) by overwriting

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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
• p P - insert the contents of the
  paste buffer after / before the
  current line/character.

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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

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Brief Introduction to vi Editor

• Global Searching and replace
• /text - Search forward for some lttextgt
• ?text - Search backward for some lttextgt
• n - Repeat the previous search for the 'next'
  occurrence
• N - Repeat the previous search but in the
  opposite direction
• ' ' (two single quotes) - Go back to where you
  where previously
• 1,s/oldtext/newtext/g - global substitutions
  

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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

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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 prompt
• 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

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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
• javac Myfile.java
• java Myfile

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Debuggin c/c file

• gdb outputfile
• To set the break
• (gdb) break filenameline 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

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Debuggin c/c file

• To watch the variables
• (gdb) watch variablename
• (gdb) watch expression
• To quit
• (gdb) q

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Thank You !!!