1 .Shell Scripting- if control STATEment programS
Conditional Statements: There are a total of five conditional statements which can be used in bash programming.
This block will process if specified condition is true. Syntax:
if [ expression ] then
An example of the code:
#Initializing two variables a=20
if [ $a == $b ] then
#If they are equal then print this echo “a is equal to b”
#else print this
echo “a is not equal to b”
If specified condition is not true in if part then else part will be executed. Syntax:
if [ expression ] then
if..elif..else..fi statement (Else If ladder)
To use multiple conditions in one if-else block, then the elif keyword is used in shell. If expression1 is true then it executes statement 1 and 2, and this process continues. If none of the conditions is true then it processes else part.
if [ expression1 ] then
elif [ expression2 ] then
2. Shell Scripting- while control statement.
Here command is evaluated and based on the result loop will executed, if command raise to false then loop will be terminated
while [CONDITION] do
The while statement starts with the while keyword, followed by the conditional expression.
The condition is evaluated before executing the commands. If the condition evaluates to true, commands are executed. Otherwise, if the condition evaluates to false, the loop is terminated, and the program control will be passed to the command that follows.
In the example below, on each iteration, the current value of the variable i is printed and incremented by one.
while [ $i -le 2 ] do
echo Number: $i ((i++))
loop iterates as long as i is less or equal than two. It will produce the following output:
3 . Shell Scripting- for control statement.
The for loop operate on lists of items. It repeats a set of commands for every item in a list.
Here var is the name of a variable and word1 to wordN are sequences of characters separated by spaces (words). Each time the for loop executes, the value of the variable var is set to the next word in the list of words, word1 to wordN.
for var in word1 word2 …wordn do
Statement to be executed done
#Start of for loop
for a in 1 2 3 4 5 6 7 8 9 10 do
# if a is equal to 5 break the loop if [ $a == 5 ]
# Print the value echo “Iteration no $a”
$bash -f main.sh Iteration no 1
Iteration no 2
Iteration no 3
Iteration no 4