UNIX - Class3 - Programming Constructs
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The document provides an overview of Unix programming constructs, particularly focusing on nested if-else statements, loops, and case statements. It showcases various examples of these constructs in shell scripting, including their syntax and usage for different scenarios. Additionally, it highlights useful shell commands such as break, continue, and exit.
![Nested ifs
You can write the entire if-else construct within either the body of the if statement of
the body of an else statement. This is called the nesting of ifs.
Ex :
chos=0
echo "1. Unix (Sun Os)"
echo "2. Linux (Red Hat)"
echo -n "Select your os choice [1 or 2]? "
read chos
if [ $chos -eq 1 ] ; then
echo "You Pick up Unix (Sun Os)"
else
if [ $chos -eq 2 ] ; then
echo "You Pick up Linux (Red Hat)"
else
echo "What you don't like Unix/Linux OS."
fi
fi
Nihar R Paital](https://image.slidesharecdn.com/class3programmingconstructs-120626111911-phpapp01/85/UNIX-Class3-Programming-Constructs-2-320.jpg)
![Multilevel if-then-else
#!/bin/ksh
echo Enter a number :
read n
if [ $n -gt 0 ]; then
echo "$n is positive"
elif [ $n -lt 0 ]
then
echo "$n is negative"
elif [ $n -eq 0 ]
then
echo "$n is zero"
else
echo "Opps! $n is not number, give number"
fi Nihar R Paital](https://image.slidesharecdn.com/class3programmingconstructs-120626111911-phpapp01/85/UNIX-Class3-Programming-Constructs-3-320.jpg)
![for Loop
1) for x in 10 20 30 40 50
do
echo $x
done
2) Ex: Arrays with for loop
#!/bin/ksh
y="shell scripting Training"
for x in ${y[*]}
do
echo $x
done
Nihar R Paital](https://image.slidesharecdn.com/class3programmingconstructs-120626111911-phpapp01/85/UNIX-Class3-Programming-Constructs-5-320.jpg)
![while loop
Syntax:
while [ condition ]
do
command1
command2
command3
..
....
done
Nihar R Paital](https://image.slidesharecdn.com/class3programmingconstructs-120626111911-phpapp01/85/UNIX-Class3-Programming-Constructs-7-320.jpg)
![Ex: while statement.
x=1
while [ $x -lt 10 ]
do
echo $x
x=`expr $x + 1`
done
Nihar R Paital](https://image.slidesharecdn.com/class3programmingconstructs-120626111911-phpapp01/85/UNIX-Class3-Programming-Constructs-8-320.jpg)
![until statement
Syntax:
until control command
do
<commands>
Done
Ex:
x=1
until [ $x -gt 10 ]
do
echo $x
x=`expr $x + 1`
done
Nihar R Paital](https://image.slidesharecdn.com/class3programmingconstructs-120626111911-phpapp01/85/UNIX-Class3-Programming-Constructs-9-320.jpg)
UNIX - Class3 - Programming Constructs
- 1. UNIX Programming Construct Presentation By Nihar R Paital
- 2. Nested ifs You can write the entire if-else construct within either the body of the if statement of the body of an else statement. This is called the nesting of ifs. Ex : chos=0 echo "1. Unix (Sun Os)" echo "2. Linux (Red Hat)" echo -n "Select your os choice [1 or 2]? " read chos if [ $chos -eq 1 ] ; then echo "You Pick up Unix (Sun Os)" else if [ $chos -eq 2 ] ; then echo "You Pick up Linux (Red Hat)" else echo "What you don't like Unix/Linux OS." fi fi Nihar R Paital
- 3. Multilevel if-then-else #!/bin/ksh echo Enter a number : read n if [ $n -gt 0 ]; then echo "$n is positive" elif [ $n -lt 0 ] then echo "$n is negative" elif [ $n -eq 0 ] then echo "$n is zero" else echo "Opps! $n is not number, give number" fi Nihar R Paital
- 4. Loops in Shell Scripts Bash supports: – for loop – while loop In each and every loop, (e) First, the variable used in loop condition must be initialized, then execution of the loop begins. (b) A test (condition) is made at the beginning of each iteration. (c) The body of loop ends with a statement that modifies the value of the test (condition) variable. Nihar R Paital
- 5. for Loop 1) for x in 10 20 30 40 50 do echo $x done 2) Ex: Arrays with for loop #!/bin/ksh y="shell scripting Training" for x in ${y[*]} do echo $x done Nihar R Paital
- 6. Ex: for statement 3) for x in `ls` do echo $x done 4) for x in `ls` `cat forloop` do echo $x done Nihar R Paital
- 7. while loop Syntax: while [ condition ] do command1 command2 command3 .. .... done Nihar R Paital
- 8. Ex: while statement. x=1 while [ $x -lt 10 ] do echo $x x=`expr $x + 1` done Nihar R Paital
- 9. until statement Syntax: until control command do <commands> Done Ex: x=1 until [ $x -gt 10 ] do echo $x x=`expr $x + 1` done Nihar R Paital
- 10. case statement. The case statement is good alternative to Multilevel if-then-else-fi statement. It enable you to match several values against one variable. Its easier to read and write. Syntax: case $variable-name in choice1) commands ;; choice2) commands ;; .... .... Esac The $variable-name is compared against the cases until a match is found. The shell then executes all the statements up to the two semicolons that are next to each other. The default is *) and its executed if no match is found. For e.g. write script as follows: Nihar R Paital
- 11. Ex: case statement echo enter value for x read x case $x in 1)ls;; 2)cal;; 3)date;; *)echo invalid esac Nihar R Paital
- 12. Useful Shell Scripting commands. break – To come out of a loop. continue – To jump to the start of loop. exit – To prematurely terminate a program. # – To interpret the rest of line as comments. Nihar R Paital
- 13. Nihar R Paital