Shell Scripting

#!/bin/bash
# The shebang tells the OS to use bash
set -euo pipefail  # exit on error, undefined var, pipe failure

# Variables (no spaces around =)
NAME="World"
echo "Hello, $NAME!"
echo "Script: $0, Arg1: $1, All args: $@"

# Command substitution
TODAY=$(date +%Y-%m-%d)
FILE_COUNT=$(ls | wc -l)
echo "Today: $TODAY, Files: $FILE_COUNT"

# if/elif/else
if [ -f "file.txt" ]; then
    echo "File exists"
elif [ -d "mydir" ]; then
    echo "Directory exists"
else
    echo "Neither exists"
fi

# for loop
for file in *.txt; do
    echo "Processing: $file"
done

# while loop
COUNT=0
while [ $COUNT -lt 5 ]; do
    echo "Count: $COUNT"
    COUNT=$((COUNT + 1))
done

#!/bin/bash
set -euo pipefail

# Function
backup() {
    local SRC=$1
    local DST=$2
    local DATE=$(date +%Y%m%d_%H%M%S)
    cp -r "$SRC" "${DST}_${DATE}"
    echo "Backed up $SRC to ${DST}_${DATE}"
}

# Error handling
if ! command -v docker &>/dev/null; then
    echo "Error: Docker not installed" >&2
    exit 1
fi

# Run backup
backup /var/www/html /backup/html

# Edit crontab
crontab -e

# Format: minute hour day month weekday command
# Run backup every day at 2am
0 2 * * * /home/bo/scripts/backup.sh >> /var/log/backup.log 2>&1

# Every 15 minutes
*/15 * * * * /home/bo/scripts/check-disk.sh

# Every Monday at 9am
0 9 * * 1 /home/bo/scripts/weekly-report.sh