Loop Control

Loop control statements give you fine-grained control over loop execution. break exits a loop early, continue skips to the next iteration, exit terminates the entire script, and return exits a function. Understanding these control mechanisms is essential for writing robust, efficient scripts that can handle edge cases and terminate gracefully!

Break Statement

The break statement immediately exits the innermost loop, regardless of the loop's normal termination condition. It's useful when you've found what you're looking for or encountered an error condition.

Click Run to execute your code

# Basic break usage
for i in {1..10}; do
    if [ $i -eq 5 ]; then
        echo "Breaking at $i"
        break
    fi
    echo "$i"
done

# Output:
# 1
# 2
# 3
# 4
# Breaking at 5

# Break in while loop
count=0
while true; do
    count=$((count + 1))
    if [ $count -ge 5 ]; then
        break
    fi
    echo "Count: $count"
done

Continue Statement

The continue statement skips the rest of the current loop iteration and jumps to the next iteration. It's useful for skipping specific cases while continuing the loop.

# Continue example: Skip even numbers
for i in {1..10}; do
    if [ $((i % 2)) -eq 0 ]; then
        continue  # Skip to next iteration
    fi
    echo "$i"  # Only prints odd numbers
done

# Output:
# 1
# 3
# 5
# 7
# 9

# Continue in while loop
count=0
while [ $count -lt 10 ]; do
    count=$((count + 1))
    if [ $((count % 3)) -eq 0 ]; then
        continue  # Skip multiples of 3
    fi
    echo "Count: $count"
done

Breaking Nested Loops

By default, break only exits the innermost loop. To break out of multiple nested loops, you need to use flags or restructure your code.

# Break only exits inner loop
for i in {1..3}; do
    for j in {1..3}; do
        if [ $j -eq 2 ]; then
            break  # Only breaks inner loop
        fi
        echo "i=$i, j=$j"
    done
    echo "After inner loop: i=$i"
done

# Output:
# i=1, j=1
# After inner loop: i=1
# i=2, j=1
# After inner loop: i=2
# i=3, j=1
# After inner loop: i=3

# Breaking outer loop using a flag
outer_done=false
for i in {1..3}; do
    for j in {1..3}; do
        if [ $i -eq 2 ] && [ $j -eq 2 ]; then
            outer_done=true
            break  # Break inner loop
        fi
        echo "i=$i, j=$j"
    done
    if [ "$outer_done" = true ]; then
        break  # Break outer loop
    fi
done

Exit vs Return

exit and return are related but different: exit terminates the entire script, while return exits only the current function.

# Exit: Terminates entire script
echo "Before exit"
exit 0  # Script stops here, exit code 0
echo "This never executes"

# Return: Exits function only
function test_function() {
    echo "Inside function"
    return 0  # Exits function, returns to caller
    echo "This never executes"
}

echo "Before function"
test_function
echo "After function"  # This executes

# Exit codes
exit 0   # Success
exit 1   # General error
exit 2   # Misuse of shell command
# ... other codes

# Return codes (functions)
return 0   # Success
return 1   # Error
# Check with $?

Common Mistakes

# Wrong - exit terminates entire script
for i in {1..10}; do
    if [ $i -eq 5 ]; then
        exit 0  # Script ends here!
    fi
    echo "$i"
done
echo "This never executes"

# Correct - break exits loop only
for i in {1..10}; do
    if [ $i -eq 5 ]; then
        break  # Only exits loop
    fi
    echo "$i"
done
echo "This executes"

# Wrong - return only works in functions
#!/bin/bash
if [ $# -eq 0 ]; then
    return 1  # Error: can only return from function
fi

# Correct - use exit in main script
#!/bin/bash
if [ $# -eq 0 ]; then
    exit 1  # Exit script with error
fi

# Wrong - break exits loop when we want to skip
for i in {1..10}; do
    if [ $((i % 2)) -eq 0 ]; then
        break  # Wrong! Exits loop entirely
    fi
    echo "$i"
done  # Only prints 1

# Correct - continue skips to next iteration
for i in {1..10}; do
    if [ $((i % 2)) -eq 0 ]; then
        continue  # Skips even numbers, continues loop
    fi
    echo "$i"
done  # Prints all odd numbers

Exercise: Control Loop Execution

#!/bin/bash
# Loop control exercises

# 1. Break example
echo "Break example (stops at 5):"
for i in {1..10}; do
    if [ $i -eq 5 ]; then
        echo "Breaking at $i"
        break
    fi
    echo "  $i"
done

# 2. Continue example
echo -e "\nContinue example (skips even):"
for i in {1..10}; do
    if [ $((i % 2)) -eq 0 ]; then
        continue
    fi
    echo "  $i"
done

# 3. Breaking nested loops
echo -e "\nBreaking nested loops:"
outer_done=false
for i in {1..3}; do
    for j in {1..3}; do
        if [ $i -eq 2 ] && [ $j -eq 2 ]; then
            echo "  Breaking at i=$i, j=$j"
            outer_done=true
            break
        fi
        echo "  i=$i, j=$j"
    done
    [ "$outer_done" = true ] && break
done

# 4. Exit vs Return
echo -e "\nExit vs Return:"
function test_return() {
    echo "  Inside function"
    return 0
    echo "  This won't execute"
}

echo "Before function"
test_return
echo "After function (script continues)"

Summary

What's Next?

Perfect! You've mastered loop control statements. Next, we'll learn about Select Menus - interactive menu loops that let users choose from options. Select loops are perfect for creating user-friendly command-line interfaces!