Linux Shell Scripting Interview Questions & Answers 2026

#!/bin/bash
# This script backs up the /etc directory — production safe
echo "Starting backup..."
cp -r /etc /backup/etc-$(date +%Y%m%d)
echo "Done."

✅ Interview Answer:

"The shebang line tells the kernel which interpreter to invoke. Using #!/bin/bash explicitly ensures the script runs under Bash regardless of what shell the user is logged into. Omitting it is a portability bug."

# Step 1: Grant execute permission
chmod +x myscript.sh

# Step 2: Run it (two valid ways)
./myscript.sh
bash myscript.sh

✅ Interview Answer:

"I use chmod +x to set the execute bit, then run with ./script.sh. In automated pipelines, I often use bash script.sh directly to avoid permission issues."

$0   # Name of the script itself
$1   # First argument passed to the script
$#   # Number of arguments passed
$?   # Exit code of the last command (0 = success)
$$   # PID of the current script
$@   # All arguments as separate words

✅ Pro Move:

Always mention $? and explain how you use it for error handling. That one detail shows production-level thinking.

#!/bin/bash
# cleanup.sh — Daily maintenance script
# Run via cron: 0 2 * * * /opt/scripts/cleanup.sh

LOG_DIR="/var/log/myapp"
BACKUP_DIR="/backup/logs"
DAYS_TO_KEEP=7

# Create backup dir if missing
mkdir -p "$BACKUP_DIR"

# Archive logs older than 7 days
find "$LOG_DIR" -name "*.log" -mtime +$DAYS_TO_KEEP -exec gzip {} \;

# Move compressed logs to backup
mv "$LOG_DIR"/*.gz "$BACKUP_DIR/" 2>/dev/null

# Report result
echo "[$(date)] Cleanup complete. Logs older than ${DAYS_TO_KEEP}d archived."

✅ Interview Answer:

"I always quote variables with double quotes to handle spaces in paths, use mkdir -p to avoid errors if the directory exists, and timestamp log output so I can trace when the script ran. This script is cron-safe and HIPAA-friendly for log retention compliance."

#!/bin/bash
set -Eeuo pipefail
# -E  → ERR trap inherited by functions and subshells
# -e  → exit immediately if any command fails
# -u  → treat unset variables as errors (no silent $UNDEFINED)
# -o pipefail → catch failures inside pipes (not just last command)

# Trap errors and print useful message
trap 'echo "ERROR: Script failed at line $LINENO" >&2' ERR

deploy_app() {
  echo "Deploying to AWS us-east-1..."
  aws s3 sync ./dist s3://my-bucket --delete
  echo "Deploy complete."
}

deploy_app

✅ Interview Answer:

"I start every production script with set -Eeuo pipefail. Without it, a failed command in the middle of a script is silently ignored and the rest runs anyway — which can cause data loss in AWS deployments or SOC2-audited environments."

# FOR loop — use when you know the list in advance
for server in web01 web02 web03; do
  echo "Checking $server..."
  ssh "$server" "systemctl status nginx"
done

# WHILE loop — use when condition drives iteration
RETRIES=0
while ! ping -c1 8.8.8.8 &>/dev/null; do
  echo "Network down, waiting... (attempt $RETRIES)"
  RETRIES=$((RETRIES + 1))
  sleep 5
  [ $RETRIES -ge 10 ] && { echo "Giving up."; exit 1; }
done
echo "Network restored."

✅ Interview Answer:

"I use for loops when iterating over a fixed list — servers, files, regions. I use while loops for polling or retry logic where the stop condition depends on runtime state."

#!/bin/bash
set -euo pipefail

APP_DIR="/opt/myapp"
BACKUP_DIR="/opt/myapp-backup-$(date +%Y%m%d-%H%M%S)"
NEW_BUILD="./dist"

rollback() {
  echo "[ROLLBACK] Deployment failed. Restoring backup..."
  rm -rf "$APP_DIR"
  cp -r "$BACKUP_DIR" "$APP_DIR"
  systemctl restart myapp
  echo "[ROLLBACK] Complete. Service restored."
  exit 1
}

trap rollback ERR

# Step 1: Backup current version
echo "Backing up current version..."
cp -r "$APP_DIR" "$BACKUP_DIR"

# Step 2: Deploy new build
echo "Deploying new build..."
rsync -av --delete "$NEW_BUILD/" "$APP_DIR/"

# Step 3: Restart and verify
systemctl restart myapp
sleep 3
systemctl is-active --quiet myapp || { echo "Service failed to start"; exit 1; }

echo "Deployment successful."

✅ Interview Answer:

"I use trap ERR to catch any failure and trigger a rollback function automatically. This pattern is used in CI/CD pipelines at AWS, GitHub Actions, and any environment where failed deploys need automatic recovery."

# Edit crontab for current user
crontab -e

# Cron syntax: min hour day month weekday command
0 2 * * *  /opt/scripts/cleanup.sh >> /var/log/cleanup.log 2>&1
30 8 * * 1 /opt/scripts/weekly-report.sh

# Debug a failing cron job:

# 1. Check if cron ran at all
grep CRON /var/log/syslog | tail -20

# 2. Run the script manually as cron would (no env vars)
env -i HOME=/root PATH=/usr/bin:/bin bash /opt/scripts/cleanup.sh

# 3. Check script output in log file
tail -50 /var/log/cleanup.log

✅ Interview Answer:

"The most common cron failure I see is PATH issues — the cron environment has almost no PATH, so commands that work manually fail silently. I always use absolute paths in cron scripts and always redirect both stdout and stderr to a log file with >> /logfile 2>&1."