Control Structures

Control structures allow your script to make decisions and repeat tasks.

1. Conditionals: if-else

In Bash, we use [ or [[ to perform tests.

#!/bin/bash
 
read -p "Enter your age: " AGE
 
if [ "$AGE" -ge 18 ]; then
    echo "You are an adult."
elif [ "$AGE" -gt 12 ]; then
    echo "You are a teenager."
else
    echo "You are a child."
fi

Common Operators

• -eq: Equal to.
• -ne: Not equal to.
• -gt: Greater than.
• -lt: Less than.
• -z: String is empty.
• -f: File exists and is a regular file.

2. Loops

for Loop

Used to iterate over a list of items.

#!/bin/bash
 
# Loop through a range
for i in {1..5}; do
    echo "Iteration $i"
done
 
# Loop through files
for FILE in *.txt; do
    echo "Processing $FILE..."
done

while Loop

Repeats as long as a condition is true.

#!/bin/bash
 
COUNT=1
while [ $COUNT -le 3 ]; do
    echo "Waiting for service... attempt $COUNT"
    ((COUNT++))
    sleep 1
done

Summary Matrix

[!TIP] Use Double Brackets Whenever possible, use [[ ... ]] instead of [ ... ]. It is more powerful and handles things like empty variables or regex much better.