TLDR; Control structures in Linux allow you to control the flow of your code. There are three main types of conditional statements in Linux: if, if-else, and if-elif-else. Looping structures in Linux include while, for, and until. Case statements allow you to execute different code blocks depending on a variable’s value.
Control Structures
Control structures are a fundamental part of programming that allow you to control the flow of your program. In Linux, there are several different control structures that you can use to control the flow of your code, including conditional statements, looping structures, and case statements.
Conditional Statements in Linux
Conditional statements in Linux allow you to execute code based on whether a certain condition is true or false. There are three main types of conditional statements in Linux: the if statement, the if-else statement, and the if-elif-else statement.
The if statement
The if statement is the simplest type of conditional statement in Linux. It allows you to execute a block of code only if a certain condition is true. Here’s an example:
if [ $x -eq 5 ]
then
echo "x is equal to 5"
fi
In this example, we use the if statement to check if the variable x is equal to 5. If it is, we execute the echo command to print a message to the console.
The if-else statement
The if-else statement is a type of conditional statement that allows you to execute one block of code if a certain condition is true, and another block of code if it is false. Here’s an example:
if [ $x -eq 5 ]
then
echo "x is equal to 5"
else
echo "x is not equal to 5"
fi
In this example, we use the if-else statement to check if the variable x is equal to 5. If it is, we execute the first echo command, and if it’s not, we execute the second echo command.
The if-elif-else statement
The if-elif-else statement is a type of conditional statement that allows you to check multiple conditions and execute different blocks of code depending on which condition is true. Here’s an example:
if [ $x -eq 5 ]
then
echo "x is equal to 5"
elif [ $x -eq 6 ]
then
echo "x is equal to 6"
else
echo "x is not equal to 5 or 6"
fi
In this example, we use the if-elif-else statement to check if the variable x is equal to 5, 6, or neither. Depending on the result, we execute different echo commands.
Looping Structures in Linux
Looping structures in Linux allow you to execute a block of code multiple times. There are three main types of looping structures in Linux: the while loop, the for loop, and the until loop.
The while loop
The while loop is a type of looping structure that allows you to execute a block of code repeatedly while a certain condition is true. Here’s an example:
x=1
while [ $x -le 5 ]
do
echo $x
x=$(( $x + 1 ))
done
In this example, we use a while loop to print the numbers 1 to 5 to the console.
The for loop
The for loop is a type of looping structure that allows you to iterate over a list of items and execute a block of code for each item. Here’s an example:
for i in 1 2 3 4 5
do
echo $i
done
In this example, we use a for loop to print the numbers 1 to 5 to the console.
The until loop
The until loop is a type of looping structure that allows you to execute a block of code repeatedly until a certain condition is true. Here’s an example:
x=1
until [ $x -gt 5 ]
do
echo $x
x=$(( $x + 1 ))
done
In this example, we use an until loop to print the numbers 1 to 5 to the console.
Case Statements in Linux
Case statements in Linux allow you to execute different blocks of code depending on the value of a certain variable. Here’s an example:
case $x in
1)
echo "x is 1"
;;
2)
echo "x is 2"
;;
*)
echo "x is not 1 or 2"
;;
esac
In this example, we use a case statement to check the value of the variable x. Depending on the value, we execute different echo commands.
