Note :- read is command to read variable form the user
.Read command reads value form keyboard up to space or enter key.
3. Logical operators
1. Arithmetic
Operators
Operator Meaning
+ Sum
-
Difference
* Product
/ Division
% Modulus
division
2. Numeric comparison
operator
Operator Meaning
-gt greater
than
-ge greater
than equal to
-lt less
than
-le less
than or equal to
-eq equal
to
-ne not
equal to
3. String
Comparison Operators
Operator Meaning
> Greater
than
< Less
than
= Equal
to
!= Not
equal to
4.Logical
Operators
Operator Meaning
-a Logical
AND
-o Logical
OR
! logical
NOT
5.Assignment operator =
In UNIX for each and every
operator, note that there should be space before and after operators.
If we don’t give space for “=”
operator it can be consider as assignment else string comparison operator
6)WAS, to read 2
float numbers and display sum, difference, product and division
$vi sp7
echo “enter 2 float numbers” read a b
c=`echo $a + $b I bc`
echo “a+b=$c”
7)WAS, to read 2
numbers an d display sum, difference, product and division
visp6
echo “enter 2 numbers”
read a b
c=`expr $a + Sb`
echo “a+b$c”
c=`expr $a - $b`
echo “a-b=$c”
c=`expr $a \* $b`
echo “a*b=$a”
c=`expr $a / $b`
echo “alb=$c”
:wq(save and quit)
Note: expr is
the command to evaluating arithmetic expressions. But expr is capable of
carring out only integer arithmetic.
....WAS, to read 2 float number and display Sum,
difference, product and division
$vi sp7
echo “enter 2 float numbers”
read a b
c=`echo $a+$b | bc`
echo”a+b=$c”
c=`echo.$a - $b | bc`
echo “a-b=$c”
c=`echo $a \* $b bc`
echo “a*b=$a”
c=`echo $a / $b | bc`
echo “alb=$c”
:wq(save and quit)
CONTROL
STATEMENTS:
There are four types of control instructions in shell.
They-are:
1. Sequence Control Instruction
2. Selection or Decision Control Instructions
3. Repetition or Loop Control Instruction
4. Case Control Instruction
The sequence control instruction ensures that the
instructions are executed in the same order in which they appear in the
program. Decision and case control instructions allows the computer to take a
decision as to which instruction is to be executed next. The loop control
instruction helps computer to executer group of statements repeatedly.
Decision Control
Statement
1. if —then-fl statement
2. if-then-else-if statement
3. if-then-elif-fi statement
4. case-esac statement
1.if-then-fi
statement
Syntax:
if control command
…………..
…………
…………..
fi
The if statement of UNIX is concerned with the the exit
status of a command. The exit status indicates whether the command was executed
successfully or not. The exit status of a command is 0 if it has been executed
successfully, 1 otherwise.
8) WAS, to change
directory
$vi sp8
echo enter directory name
read dname
if cd $dname
then
echo “changed to $dnarne”
pwd
fi
:wq(save and quit)
2.Jf-then-else-fi
Statement
syntax
if condition
then
………
………
else
………
………
fi
The exit status of the control command is 0 then it
executes then statement otherwise it executes else statements.
9) WAS, to copy a
file
$vi sp9
echo enter source filename and target file and name
read src trg
if cp $src
$trg
then
echo file copied
successfully
else
echo failed to
copy the file
fi
:wq(save and quit)
10) WAS, to search string in a file
$vi sp10.sh
echo “enter a file name”
read fname
echo “enter to string to search”
read str
if grep $str $fname
then
echo “$str is found in the file $file”
else
echo “$str is not found in $fname”
fi
:wq(save and quit)
11)WAS, to find
greatest number of 2 numbers
vi sp 11
echo enter two numbers
read a b
if [ $a –gt $b ]
then
echo $a is the greatest value
else
echo $b is the greatest value
fi
:wq(save and quit)
12) WAS, to check
given no is even or odd
$vi sp12
echo enter a number
read n
if [ `expr $n %
2` -eq
0 ]
then
echo $n is even number
else
echo $n is odd number
fi
:wq(save and quit)
The Test Command
If constructs depends upon whether or not the condition
results into true or not.
If constructs are generally used in conjunction with the
test command. The test command helps us to find the contents of a variable, the
number of variables and the type of file or kind of file permission. The test
command returns an exit status after evaluating the condition.
Syntax: -
If test condition
Then
Commands
Else
Commands
fi
13) WAS, to check
how many users working on the system
$vi sp13
total=`who | wc –l`
if [ $total
-eq 1 ]
then
echo “you are the only user working…
else
echo “there are $total user working…
fi
:wq(save and quit)
14) WAS,
to check given number is +ve or –ve number
$vi sp14
echo “enter a number”
read num
if test $nurn
-gt 0
then
echo “$num is +ve number” else
echo “$num is —ve number”
fi
;wq(save and quit)
15) WAS, to find student result
4vispl5
echo “enter three subject marks:”
read ml m2 m3
if [ $ml
-ge 40 ]
then
if [ $m3
-gt 40 ]
then
if [
$m3 –gt 40 ]
then
echo “PASS”
else
echo “FAIL”
fi
else
echo “FAIL”
fi
else
echo “FAIL’
fi
:wq(save and qut)
16)WAS, to print
greeting
$vi spl6
hour=`date | cut
-c 12,33`
if [ $hour
—ge 0 —a
$hour —le 11]
then
echo “Good Morning”
else
if [
$hour -ge 12
-a $hour -Ie 17 ]
then
echo “Good Afternoon”
else
echo “Good Evening”
fi
fi
:wq(save and quit)
File Test Commands
The test command has several options for checking the
status of a file.
-e True
if the file exist.
-s True if the file exists and has a
size greater than 0
-f True
if the file exists and is not directory
-d True
if the file exists and is a directory file
-c True
if the file exists and character special file
-b True
if the file exists is a block special file
-r True
if the file exists and have a read permission to it
-x True
if the file exists and have a execute permission to it
-w True if
the file exists and have a write permission to it
17) WAS, to check for ordinary file and display it
contents
$vi sp17
echo enter a file name
read fname
if test -f $fname
then
cat $fname
else
echo “given file is not ordinary file”
:wq(save and quit)
18) WAS, to check give file is ordinary or directory file
$vi sp18
echo “enter a file name:”
read fnarne
if [ -f $fname ]
then
cat $fname
elif [ -d
$fname ]
then
ls
else
echo $fname is not file and not a directory
fi
:wq(save and quit)
19) WAS, to check
read permission
$vi sp19
echo “enter a file name
read fname
if [ -r
$fname ]
then
cat $fname
else
chmod u+r $fname
cat $fname
fi
:wq(save and quit)
20) WAS, to append
data to the file
$vi sp20
echo “enter a filename”
read $fname
if [ -f
$fname ]
then
if [ -w
$fname ]
then
echo “enter
data to file to stop press ctrl+d...”
cat >>$fnarne
else
chmod u+w
$fname
echo “enter
data to file to stop press ctrl+d…”
cat >>$fname
fi
else
echo “enter data to file to stop press ctrl+d…”
cat >>$fname
fi
:wq(save and quit)
String Test
Commands
Condition Meaning
String 1 = string2 True
if the strings are same
Stringi != string2 True
if the strings are different
-n string 1 True
if the length of string is greater than 0
-z string True
if the length of the string is zero
21) WAS, to
compare two strings
$vi sp21.sh
echo “enter first string:”
read str1
echo “enter second string:”
read str2
if test $str1
= $str2
then
echo “both strings are equal”
else
echo “strings are not equal”
fi
:wq(save and quit)
22) WAS, to check
given string is empty or not
$vi sp22
echo enter a string
read str
if [ -z
$str ]
then
echo “string is empty”
else
echo ‘given string is not empty”
fi
:wq(save and quit)
Case Control
Statement
Syntax -
Case value in
Choicel)
…………..
…………..
‘’
‘’
cho ice2)
………
………
‘’
‘’
choice3)
………
………
‘’
‘’
esac
Firstly, the expression following the case keyword is
evaluated. The value that it yields is then matched, one by one against the
potential choices (choice1, choice2 and choice3 in the above form). When a
match is found, the shell executes all commands in that case up to;;. This pair
of semicolons placed at the end of each choice is necessary.
23)Sarnple program
for case
$vi sp23
echo “enter a number between 1 to 4”\c”
read num
case $nurn in
1)echo “you entered 1” ;;
2)echo “you entered 2” ;;
3)echo “you entered 3” ;;
4)echo “you entered 4” ;;
*)echo “invalid number, enter number between 1to4 only”
;;
esac
:wq(save and quit)
24) WAS, to check
given character is upper case alphabet or lower case alphabet or digit or special
character
$vi sp24
echo “enter a single character”
read ch
case $ch in
[a-z])echo “you
entered a small case alphabet” ;;
[A-Z])echo “you entered
a upper case alphabet” ;;
[0-9])echo “you
entered a digit” ;;
?)echo “you
entered a special character”;;
*)echo “you entered more than one character”;;
esac
:wq(save and quit)
25)WAS, to display
file conten ts or write on to file or execute based on user choice
$vi sp25
echo “enter a file name:\c”
read fname
echo
“Main Menu”
echo
“======================”
echo “r. read
mode”
echo “w.write
mode”
echo “x. execute
mode”
echo “enter
mode:\c”
read mode
case $mode in
r)
if [ -f
$fname -a -r
$fname ]
then
cat $fname
fi
;;
w)
if [ -f $fname
-a -w $fname
]
then
echo “enter data to file at end press ctrl+d:”
cat >$fname
fi
;;
x)
if [ -f
$fname -a -x
$fname ]
then
chmod u+x $fname
$fname
fi
;;
*)echo ”you
entered invalid mode…”
;;
esac
:wq(save and quit)
Looping Control
Statements
A loop involves repeating some portion of the program
either a specified no of times of times or until a particular condition is
being satisfied. There are three methods by way of which we can repeat a part
of a program. There are
1) Using a while
statement
2) Using a until
statement’
3) Using a for
statement
While Statement
Syntax
while [condition j
do
……………
……………
……………
done
The statements within the while loop would keep on
getting executed till the condition is true. When the condition is false, the
control transfers to after done statement.
27) WAS, to
display numbers 1 to 10
$visp27
echo “the number form 1 to 10 are:”
i=1
while [ $i
-Ie 10 ]
do
echo $i
i=`expr $i + 1`
done
:wq(save and quit)
28) WAS, to copy
file from root to user directory
$vi sp28
flag=1
while [ $flag
-eq 1 ]
do
echo “enter a filename”
read fname
cp $fname /usr/sv/$fname
echo “$fname copied………..”
echo “do u wish to continue [1 -yes/0-no]: ”
read flag
done
:wq(save and quit)
The Break
Statement
When the keyword break is encountered inside any loop,
control automatically passes to the first statement after the loop.
The Continue
Statement
When the keyword continues is encountered inside any
loop, control automatically passes to the beginning of the loop.
29)WAS, to display
file contents if file existing
$vi sp29
x0
while test $x=0
do
echo “enter a file name:\c”
read fname
if test ! –f
$fname
then
echo “$fname is not found………..”
continue
else
break
fi
done
cat $fnarne | more
:wq(save and quit)
The Until Loop
Syntax
until [condition j
do
……………
……………
……………
done
The statements within the until loop keep on getting
executed till the condition is false. When the condition is true the control
transfers to after done statement.
30) WAS, to print
numbers 1 to 10
$vi sp3O
i=1
until [ $i
-gt 10 ]
do
echo $i
i=`expr$i+1`
done
:wq(save and quit)
The True and False
Command
To execute the loop an infinite
no of times.
31) Write sample
program for true command
$vi sp3l
while true
do
clear
banner “hello”
sleep 1
clear
banner “Tecnosoft”
sleep 1
done
:wq(save and quit)
Note: The above program executes continuous to stop
execution press ctrl + break
32) Write sample
program for false command
$vi sp32
until false
do
clear
banner “hello”
sleep 1
clear
banner “Tecnosoft”
sleep 1
done
:wq(save and quit)
The Sleep Command
The sleep command stops the execution of the program the
specified no of seconds.
The For Loop
Syntax
For variable in
va1ue1value2 value3 . ... . value
do
………………….
……………….
done
The for allows us to specify a list of values which the
variable in the loop can take. The loop is then executed for each value
mentioned in the list.
33) WAS, to
demonstrate for loop
$vi sp33
for i in 1 2 3 4 5
do
echo $i
done
:wq(save and quit)
34) WAS, to
demonstrate for loop
$vi sp34
for i in Multics is a training institute.
do
echo $i
done
:wq
35) WAS,to display
all files in current directory
$vi sp35
for i in *
do
if test -f
$i -a -r $i
then
cat $i |more
sleep 1
clear
fi
done
:wq(save and quit)
36)WAS, to display
all sub-directories in the current directory
$vi sp36
for I in*
do
if [ -d $i ]
then
echo $i
fi
done
:wq(save and quit)
Positional
Parameters
When the arguments are passed with the command line,
shell puts each word on the command line into special variables. For this, the
shell uses something called as “positional parameters;. These can be thought of
as variables defined by the shell, They are nine in number, named $1 through
$9.
Consider the following statement, where sp37 is any
executable shell script file and the remaining are the arguments
$sp37 Multics is a computer training and development institute
On entering such command, each word is automatically
stored serially in the positional parameters. $1 through $9
37) write program to
copy a file using positional parameters
vi sp37
if cp $1 $2
-
then
echo “file copied successfully”
else
echo “failed to copy”
fi
:wq(save and quit)
$chmod 744 sp37
$sp37 al a2
in above command it passes al to $1 and a2 into $2, then
it copies al
contents to a2.
Special Characters
$*, $@ Contains entire string of arguments
$# - Contains
the no for argument specified in the command
$? Holds
the value of exit status of the previous command
$$ Holds
user parent id
