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
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
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
