break - Linux

Overview

The break command in Linux is a shell builtin that exits from a loop (for, while, until, or select) in shell scripting. This command is used primarily within scripts to terminate the execution of loops based on specific conditions, thus allowing for more granular control of script flow.

Syntax

The basic syntax of the break command is as follows:

break [n]

Where [n] is an optional argument representing the number of enclosing loops to break out of. If n is omitted, it defaults to 1, meaning it will exit only the current loop.

Options/Flags

The break command has only one optional argument:

n : An integer which specifies the number of nested loops to exit. This allows breaking out of multiple loops with a single break command. If n is greater than the number of enclosing loops, all enclosing loops are exited.

Examples

Basic Example
Exit a loop after processing five items:

for i in {1..10}; do
    if [ $i -eq 6 ]; then
        break
    fi
    echo "Processing item $i"
done

Advanced Example
Exiting multiple loops:

for i in {1..5}; do
    for j in {1..5}; do
        if [ $i -eq 3 -a $j -eq 3 ]; then
            break 2  # Breaks out of both loops
        fi
        echo "Processing item $i, $j"
    done
done

Common Issues

Exceeding Loop Count
Using a number with break that exceeds the number of nested loops will not produce an error; instead, it breaks out of all possible loops.
Misplacement
Placement of break outside of any loop will cause a syntax error. Ensure that break is used within a loop structure.

Integration

break is often combined with other commands and constructs to effectively manage script workflows:

num=0
while true; do
    num=$((num+1))
    read -p "Continue (y/n)? " answer
    if [ "$answer" = "n" ]; then
        break
    fi
    echo "Iteration $num"
done
echo "Loop has been exited."

continue – Skips the remainder of the current loop iteration and begins the next iteration.
exit – Exits the shell or a shell script entirely.

For more details and advanced usage, you might consider reviewing the official Bash documentation here.