1. Lab 8 Shell Script Reference:
Linux Shell Scripting Tutorial v1.05r3 A Beginner's handbook

2. Positional parameters or command line arguments
Special shell variables $0…$9
Positional parameters or command line arguments
myscript foo bar
myscript $0
foo $1
Bar $2
$# tells you how many parameter your script was given

3. if condition
if condition which is used for decision making in shell script, If given condition is true then command1 is executed.
Syntax:
if condition
then
command1... fi
-cat command:
Display text files on screen.
cat file-name

4. test expression or [ expr ]
- -True  return zero(0)
Is used to see if an expression is true
- -False returns nonzero
Syntax: test expression OR [ expression ]
$ vi ispositive
# Script to see whether argument is positive # if test $1 -gt 0 then echo "$1 number is positive" fi
Run it as follows:
$ chmod 755 ispositive
$ ./ispositive 5

8. test expression or [ expr ]
For test statement with if commandFor [ expr ] statement with if command
Mathematical Operator in  Shell Script Meaning
if [ 5 -eq 6 ]
if test 5 -eq 6
is equal to
-eq
if [ 5 -ne 6 ]
if test 5 -ne 6
is not equal to
-ne
if [ 5 -lt 6 ]
if test 5 -lt 6
is less than
-lt
if [ 5 -le 6 ]
if test 5 -le 6
is less than or equal to
-le
if [ 5 -gt 6 ]
if test 5 -gt 6
is greater than
-gt
if [ 5 -ge 6 ]
if test 5 -ge 6
is greater than or equal to
-ge

9. test expression or [ expr ]
String Comparisons
Meaning
Operator           
string1 is equal to string2
string1 = string2
string1 is NOT equal to string2
string1 != string2
string1 is NOT NULL or not defined 
string1
string1 is NOT NULL and does exist
-n string1
string1 is NULL and does exist
-z string1

10. test expression or [ expr ]
Logical Operators
Meaning
Operator           
Logical NOT
! expression
Logical AND
expression1  -a  expression2
Logical OR
expression1  -o  expression2

11. if …else…fi
If given condition is true then command1 is executed otherwise command2 is executed.
Syntax:
if condition
then
command1
else
if condition is not true then execute all commands up to fi fi

12. Exercise ( if..else with parameters)
if [ $# -eq 0 ]
then
echo " Enter one argument “
exit 1
else
  echo " The first argument is $1 " fi

14. if …else…fi $ chmod 755 isnump_n $ ./isnump_n 5
$ vi isnump_n
# Script to see whether argument is positive or negative if [ $# -eq 0 ] then echo "$0 : You must give/supply one integers" exit 1 fi
if test $1 -ge 0 then echo "$1 number is positive" else echo "$1 number is negative" fi
$ chmod 755 isnump_n
$ ./isnump_n 5

16. if …else…fi Syntax: if condition Then then ..... .. do this else ....

17. Nested if-else-fi
$ vi nestedif
osch=0 echo "1. Unix (Sun Os)" echo "2. Linux (Red Hat)" echo –n "Select your os choice [1 or 2]? " read osch if [ $osch -eq 1 ] ; then      echo "You Pick up Unix (Sun Os)" else        if [ $osch -eq 2 ] ; then              echo "You Pick up Linux (Red Hat)"        else              echo "error only 1 or 2"        fi fi
$ chmod 755 nestedif
$ ./ nestedif

20. Multilevel if-then-else
Syntax:
if condition
then
condition is zero (true - 0)
execute all commands up to elif statement
elif condition1 then
condition1 is zero (true - 0)
elif condition2
condition2 is zero (true - 0)
else
None of the above condtion,condtion1,condtion2 are true
(i.e. all of the above nonzero or false)
execute all commands up to fi fi

21. $ vi elf
# Script to test if..elif...else # if [ $1 -gt 0 ]; then   echo "$1 is positive" elif [ $1 -lt 0 ] then   echo "$1 is negative" elif [ $1 -eq 0 ] then   echo "$1 is zero" else   echo "Opps! $1 is not number, give number" fi
$ chmod 755 elf
$ ./ elf 8
$ ./ elf -3
$ ./ elf 0
$ ./ elf a

22. for Loop
Syntax:
for { variable name } in { list } Do
execute one for each item in the list until the list is not finished (And repeat all statement between do and done)
done
$ vi testfor
for NUMBER in do echo "Welcome $NUMBER times" done
$ vi for2
LIMIT = 10
for ((  i = 1 ;  i <= LIMIT;  i++  )) do   echo "Welcome $i times" done

24. for Loop
$ vi nestedfor
for (( i = 1; i <= 5; i++ ))      ### Outer for loop ### do     for (( j = 1 ; j <= 5; j++ )) ### Inner for loop ###     do           echo -n "$i "     done   echo "" #### print the new line ### done

25. while loop Syntax: i=$1 while test $i != 0 do echo –n "$i ,"
while [ condition ] do
command1
command2
command3
done
Write script to print numbers as 5,4,3,2,1, using while loop. The biggest number is supplied as command line argument.
i=$1
while test $i != 0 do
echo –n "$i ,"
i=`expr $i - 1`
done
echo " "

26. for (( i=1; i<=5; i++ )) do for (( j=1; j<=i; j++ ))
Exercise (1) Write shell script using for loop to print the following patterns .
for (( i=1; i<=5; i++ )) do
for (( j=1; j<=i; j++ ))
echo -n "$i"
done
echo ”“