003 scripting
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  • 1. SHATRIXScripting A  Creating and Running Scripts  Basic Script Architecture G  echo E  Variables N read   Conditional statements D  Loops A  Examples
  • 2. Creating and Running Scripts Scripts are normal text files with x permission  touch  script­name  chmod  777  script­name  chmod  u+x  script­name To run a script:  full path  ./script­name  sh  script­name  bash  script­name
  • 3. Basic Script Architecure #!(shell-path) #!/bin/bash  variables definition  echo ”Welcome”  read var1  read variables from user  echo $var1  loops  conditional statements  print output to terminal  pipe & redirection to other files
  • 4. echo echo displays a line of text  echo  ”string”  echo  $variable­name  echo  ”string  $var­name”  echo  ”string  $var­name  another­string”  echo $(command) echo ”Welcome Linux users”
  • 5. Variables Define a variable  variable­name=VALUE Print a variable to screen  echo  $variable­name System variables:  Normal: has to be changed with each user  HOME     PWD    SHELL  Environmental: changes with the login shell only  login shell with (su ­)  PATH env
  • 6. read read take a value from the user to a variable  read  variable­name  read  ­p  ”string”  variable­name read  ­p  ”Enter your name”  name echo  ”Your name is $name”
  • 7. Conditional Statements if statement #!/bin/bashif [ condition ] x=5 if [ $x = 5 ] then then   things to do echo ”right” elif [ another­cond. ] else echo ”wrong” then fi   things to do else   things to dofi
  • 8. Conditional Statements case statement #!/bin/bashcase $variable­name in x=5   value_1) case $x in      things to do;; 4) echo ”x=4”;;   value_2) 5)      things to do;; echo ”x=5” echo ”ok”;;   *) *)      default action;; echo ”I dont know”;;esac esac
  • 9. Loops for loopfor  VARIABLE  in  ARRAYdo    things on each valuedone #!/bin/bash for i in 1 2 3 4 5 do echo ”current value is $i” done
  • 10. Loops while loopwhile  [ condition ]do #!/bin/bash    things to do VAR=0done while [ $VAR ­lt 3 ]; do    echo $VAR    VAR=$[$VAR+1] equal (=) done not equal (!=) Less than (­lt) Greater than (­gt)
  • 11. Examples (User Login) #!/bin/bash user_name="shatrix" password="13" read ­p "User Name: " login_name stty ­echo read ­p "Password: " login_pass stty echo echo "" if [ $login_name = $user_name ];  then if [ $login_pass = $password ];  then echo "Now you are logged in....." else echo "Error, wrong password, try again" fi else echo "Error, user name doesnt exist" fi
  • 12. Examples (Calculator) #!/bin/bash read ­p "Enter First Number: " f_num read ­p "Enter Second Number: " s_num read ­p "Enter Operation: " op case $op in +)     echo "$f_num + $s_num = $[$f_num+$s_num]";; ­)     echo "$f_num ­ $s_num = $[$f_num­$s_num]";; x)     echo "$f_num x $s_num = $[$f_num*$s_num]";; /)     echo "$f_num / $s_num = $[$f_num/$s_num]";; esac
  • 13. Examples (Modified Calculator) #!/bin/bash read ­p "Enter First Number: " f_num read ­p "Enter Second Number: " s_num read ­p "Enter Operation: " op case $op in +)     echo "$f_num + $s_num = $[$f_num+$s_num]";; ­)     echo "$f_num ­ $s_num = $[$f_num­$s_num]";; x)     echo "$f_num x $s_num = $[$f_num*$s_num]";; /)     if [ $s_num != 0 ];  then       echo "$f_num / $s_num = $[$f_num/$s_num]"     else       echo "Error, division by zero"     fi;; *)     echo "Wrong operation, please try again !!!" esac
  • 14. Examples (PhoneBook)