Shell script - 3

Shell script - 3

To go to Session 1 click here
To go to Session 2 click here
To go to UNIX basic commands click here

Starting with “hello”

            The basic things for any program is input and output this can be achived using the two commands

1.      echo which similar to printf in c

2.      read which similar to scanf in c

First script

Example 7

            #!/bash/sh

            echo “hello”

            echo “Enter ur name”

            read nam

            echo “This is my first program $nam”

The Branching Statements

The next important thing in programming is branching to do a specific task based on specific condition.

1.      if .. fi

2.      if..else..fi

3.      if..elif..else..fi

4.      case..esac

if..fi syntax

if [ condition ]

then

            statements

fi

if..else..fi syntax

if [ condition ]

then

            statements

else

            statements

fi

if..elif..fi syntax

if [ condition ]

then

            statements

elif [ condition ]

            statements

else

            statements

fi

in these condition branching statements can be nested or there may be more than one elif based on requirements.

Example 7:

            #!/bin/sh

            filename=$1

if [-r filename] then

echo "file is readable"

elif [-x filename] then

echo "file is executable"

elif [-w filename] then

echo "file is writable"

else

echo "ERRROR: $filename HAS PERMISSION PROB"

fi

            case..esac syntax

            case variable in

                        pattern1)

                                    statements

                        ;;

                        pattern2)

                                    statements

                        ;;

                        ……

                        ……

                        patternn)

                                    statements

                        ;;

            esac

Example 8:

            #!/bin/sh

            name=$1

            case $name in

                        “jaya”)

                                    echo “Welcome buddy”

                                    ;;

                        “devi”)

                                    echo “Welcome sir”

                                    ;;

                        “Shiv”)

                                    echo “Welcome $name”

                                    ;;

            esac

Output

Testhome/l685360# ./test jaya

Welcome buddy

Testhome/l685360#

           

The looping

            The next important thing in programming is looping to do a specific task for some n times loops available in shell script are:

1.      while

2.      for

3.      unitil

4.      select

While Loop:

            Syntax:

                        While [ condition ]

                        do

                                    statements

                        done

Example 9:

#!/bin/sh

echo "Enter n "

read n

i=0

while [ $i -le $n ]

do

        echo "Welcome"

        i=`expr $i+1 `

done

Out Put:

            Testhome/l685360# ./test

Enter n

2

Welcome

Welcome

Welcome

Testhome/l685360#

*note : break can be used to break the loop

*note : continue can be used to continue the looping without executing the rest of lines.

            Example:

                        n=0

                        While [ $n < 10]

                        do

                                    if[ $n == 1]

                                    then

                                                continue;

                                    fi

                                    #if n==1 n becomes true it goes directly go to continue the loop without incrementing because of this, this loop will be endless loop

                                    n=`expr $n+1`

                        done

For loop:

Example 10:

#i!/bin/sh

n1="0 1 2 3 4 5 6 7 8 9 0 10"

for n in $n1

do

        echo $n

        echo "Welcome"

done

Out put:

Testhome/l685360# ./test

0

Welcome

1

Welcome

2

Welcome

3

Welcome

4

Welcome

5

Welcome

6

Welcome

7

Welcome

8

Welcome

9

Welcome

0

Welcome

10

Welcome

Testhome/l685360#

Until loop:

Until syntax:

 until  [ condition ]

 do

            statements

 done

Example 11:

#!/bin/sh

n = 10

x=0

until [ $x –lt $n ]

do

            echo $x

            x = `expr $x + 1`

done

Select Loop:

Select loop syntax:

select variable in word1 word2 …. Wordn

do

            statements

done

Example 12:

#!/bin/sh

select food in breakfast lunch dinner

do

        if [ $food == "breakfast" ]

        then

                echo "Good morning"

        elif [ $food == "lunch" ]

        then

                echo "Good After noon"

        elif [ $food == "dinner" ]

        then

                echo "Good night"

        else

                echo "Invalid option"

        fi

done

                       

Out put:

Testhome/l685360# ./test

1) breakfast

2) lunch

3) dinner

#? 1

Good morning

#? 2

Good After noon

#? 3

Good night

#?
Don't forget to put your feed back as comments which encourages me to do this and you can also post your questions or solve/give answers for others questions, Thanks in advance friends.....

To go to session 4 click here