Bash For Loops Explained

Basic Bash for loop syntax

The basic pattern is:

for item in list; do
  command "$item"
done

Example:

for name in alpha beta gamma; do
  echo "$name"
done

alpha
beta
gamma

The variable name changes on each loop. First it is alpha, then beta, then gamma.

Loop through files

A common use for for loops is running a command against matching files.

for file in *.log; do
  echo "Found log file: $file"
done

Found log file: access.log
Found log file: error.log
Found log file: debug.log

The shell expands *.log before the loop runs. That means the loop sees a list of matching filenames.

Safely handle missing matches

If no .log files exist, Bash may leave the pattern unchanged. This can produce confusing output.

for file in ./*.log; do
  [ -e "$file" ] || continue
  echo "$file"
done

The line [ -e "$file" ] || continue means: if the path does not exist, skip this loop item.

Be careful looping through command output

This pattern is common, but risky:

for file in $(find . -name "*.log"); do
  echo "$file"
done

It breaks when filenames contain spaces, tabs or unusual characters. A safer pattern is:

find . -name "*.log" -print0 | while IFS= read -r -d '' file; do
  echo "$file"
done

./access.log
./old logs/error log 2026.log
./debug.log

For simple beginner scripts, looping over ./*.log is fine. For recursive file searches, prefer the safer find -print0 pattern.

Loop through a Bash array

Arrays are useful when you have a fixed list, such as services or domains.

SERVICES=("nginx" "mysql" "sshd")

for service in "${SERVICES[@]}"; do
  echo "$service"
done

nginx
mysql
sshd

The quoted "${SERVICES[@]}" form is the safe way to loop through each array item.

Check multiple Linux services

#!/usr/bin/env bash

SERVICES=("nginx" "mysql" "sshd")

for service in "${SERVICES[@]}"; do
  if systemctl is-active --quiet "$service"; then
    echo "[OK] $service is running"
  else
    echo "[WARN] $service is not running"
  fi
done

[OK] nginx is running
[WARN] mysql is not running
[OK] sshd is running

This is a practical loop for Linux troubleshooting. For more service commands, see the systemd guide.

Check multiple domains with dig

#!/usr/bin/env bash

DOMAINS=("example.com" "example.org" "commandlinequiz.com")

for domain in "${DOMAINS[@]}"; do
  echo "== $domain =="
  dig +short "$domain"
  echo
done

== example.com ==
93.184.216.34

== example.org ==
93.184.216.34

== commandlinequiz.com ==
104.21.10.123
172.67.150.45

For more DNS troubleshooting, read the dig command guide.

C-style Bash for loops

Bash also supports a counting style loop.

for ((i = 1; i <= 5; i++)); do
  echo "Attempt $i"
done

Attempt 1
Attempt 2
Attempt 3
Attempt 4
Attempt 5

This is useful for counters, retries and simple repeated attempts.

Using break and continue

continue skips to the next loop item. break exits the loop completely.

for file in ./*.log; do
  [ -e "$file" ] || continue

  if [ "$file" = "./error.log" ]; then
    echo "Found error.log"
    break
  fi
done

Found error.log

Common Bash for loop mistakes

Practice exercises

1. Loop through three service names and print each one.
2. Loop through all .txt files and print their size with ls -lh.
3. Loop through a list of domains and run dig +short.
4. Loop through log files and count lines with wc -l.