30. Loops: for and while Loops for Repetitive Tasks

Loops are essential for automating tasks that need to be performed multiple times, such as processing a list of files or repeating until a condition is met.

1. The for Loop (Iterating over a list)

The for loop iterates over a defined list of items (words, files, numbers).

Syntax:

bash for VARIABLE in LIST_OF_ITEMS; do # Commands using $VARIABLE done

Example: Processing Log Files

bash #!/bin/bash

LOGS=$(ls *.log)

for logfile in $LOGS; do echo "Processing $logfile..." # Example: Check the last line of the log tail -n 1 $logfile done

2. The while Loop (Repeating until Condition is False)

The while loop continues executing commands as long as the condition remains true.

Syntax:

bash while [ condition ]; do # Commands done

Example: Countdown Timer

bash #!/bin/bash

COUNTER=5

while [ $COUNTER -gt 0 ]; do echo "$COUNTER seconds remaining..." sleep 1 # Wait for 1 second COUNTER=$((COUNTER - 1)) done

echo "Time's up!"

(Note: $(( )) is used for arithmetic operations in Bash.)