Syntax for a for Loop in Bash

The for loop in Bash is a control structure that allows you to iterate over a list of items or a range of numbers. It is particularly useful when you know the number of iterations in advance. Below, we will explore the syntax of the for loop in detail, along with sample code.

Basic Syntax of the for Loop

The basic syntax of a for loop in Bash is as follows:

for variable in list
do
    # commands to execute for each item
done

In this syntax:

• variable is the name of the variable that will hold the current item from the list during each iteration.
• list is a space-separated list of items or a range of numbers.
• The do keyword indicates the start of the commands to be executed for each item.
• The done keyword marks the end of the for loop.

Example of a for Loop

Here’s a simple example of using a for loop to iterate over a list of fruits:

#!/bin/bash
# Using a for loop to iterate over a list of fruits
for fruit in apple banana cherry
do
    echo "I like $fruit"
done

In this example:

• The loop iterates over the list of fruits: apple, banana, and cherry.
• For each fruit, it prints a message indicating that the user likes that fruit.

Using a for Loop with a Range

You can also use a for loop to iterate over a range of numbers. The syntax for this is:

for variable in {start..end}
do
    # commands to execute for each number
done

Here’s an example that prints numbers from 1 to 5:

#!/bin/bash
# Using a for loop with a range
for i in {1..5}
do
    echo "Number $i"
done

In this example:

• The loop iterates over the numbers from 1 to 5.
• For each number, it prints the current number.

Using C-style Syntax in a for Loop

Bash also supports a C-style syntax for for loops, which is useful for more complex iterations:

for (( initialization; condition; increment ))
do
    # commands to execute
done

Here’s an example using C-style syntax to print numbers from 1 to 5:

#!/bin/bash
# Using C-style for loop
for (( i=1; i<=5; i++ ))
do
    echo "Number $i"
done

In this example:

• The loop initializes i to 1, checks if i is less than or equal to 5, and increments i by 1 in each iteration.
• For each number, it prints the current value of i.

Conclusion

The for loop in Bash is a versatile tool for iterating over lists and ranges. It allows for clear and concise code, making it easier to perform repetitive tasks. By understanding the different syntaxes available, you can choose the most appropriate one for your specific use case, enhancing the efficiency and readability of your scripts.