Shell

Google Shell Style Guide

Official Google Shell scripting standards for consistent, maintainable Bash scripts.

Quick Reference

Golden Rules

1. Use `#!/bin/bash` — specify interpreter 2. Quote variables — "$var" not $var 3. Check exit codes — set -e or explicit checks 4. Use functions — organize code logically 5. Avoid parsing `ls` — use globs or find 6. Use `[[` over `[` — more features, fewer gotchas 7. ShellCheck for linting — catch common mistakes

Naming Conventions (Preview)

Basic Patterns (Preview)

#!/bin/bash
# ✓ CORRECT

set -euo pipefail  # Exit on error, undefined vars, pipe failures

readonly SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"

function main() {
  local user_count="$1"
  
  if [[ -z "${user_count}" ]]; then
    echo "Error: user_count required" >&2
    return 1
  fi
  
  echo "Processing ${user_count} users"
}

main "$@"

When to Use This Guide

• Writing new shell scripts
• Refactoring existing scripts
• Code reviews
• Setting up ShellCheck
• Onboarding new team members

Install

npx skills add testdino-hq/google-styleguides-skills/shell

Full Guide

See shell.md for complete details, examples, and edge cases.

Google Shell Style Guide

Source: https://google.github.io/styleguide/shellguide.html

Golden Rules

1. Use Bash — #!/bin/bash for all shell scripts 2. 2-space indentation — no tabs 3. 80-character line limit — for readability 4. Quote variables — always use "${var}" 5. Check return values — never ignore errors 6. Use ShellCheck — lint your scripts 7. Keep scripts under 100 lines — or rewrite in another language

---

1. File Structure

#!/bin/bash
#
# Brief description of script purpose.
# Detailed usage information if needed.

set -euo pipefail  # Exit on error, undefined vars, pipe failures

readonly SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
readonly CONST_VALUE="constant"

main() {
  # Main script logic here
  do_something "$@"
}

do_something() {
  local arg="$1"
  echo "Processing: ${arg}"
}

main "$@"

---

2. Naming

---

3. Functions

# CORRECT - function with comments
#######################################
# Cleanup files from backup directory.
# Globals:
#   BACKUP_DIR
# Arguments:
#   None
# Returns:
#   0 on success, 1 on error
#######################################
cleanup() {
  local file
  for file in "${BACKUP_DIR}"/*; do
    rm "${file}" || return 1
  done
  return 0
}

# CORRECT - function call
cleanup || {
  echo "Cleanup failed" >&2
  exit 1
}

---

4. Variables

# CORRECT - always quote variables
echo "${my_var}"
echo "${1}"
echo "${file_name}"

# CORRECT - use local in functions
my_function() {
  local local_var="value"
  echo "${local_var}"
}

# CORRECT - readonly for constants
readonly MAX_RETRIES=3
readonly CONFIG_FILE="/etc/myapp.conf"

# AVOID - unquoted variables
echo $my_var  # AVOID
echo $1  # AVOID

---

5. Conditionals

# CORRECT - use [[ ]] for tests
if [[ -f "${file}" ]]; then
  echo "File exists"
fi

if [[ "${var}" == "value" ]]; then
  do_something
fi

if [[ -z "${var}" ]]; then
  echo "Variable is empty"
fi

# CORRECT - numeric comparisons
if (( count > 10 )); then
  echo "Count is greater than 10"
fi

# AVOID - use [ ] (old test command)
if [ -f "${file}" ]; then  # Use [[ ]] instead
  echo "File exists"
fi

---

6. Loops

# CORRECT - iterate over array
for item in "${array[@]}"; do
  process "${item}"
done

# CORRECT - C-style for loop
for (( i = 0; i < 10; i++ )); do
  echo "${i}"
done

# CORRECT - while loop
while read -r line; do
  echo "Line: ${line}"
done < "${file}"

# CORRECT - process substitution (not pipe to while)
while read -r line; do
  echo "${line}"
done < <(command)

---

7. Error Handling

# CORRECT - check return values
if ! command; then
  echo "Command failed" >&2
  exit 1
fi

# CORRECT - use || for error handling
command || {
  echo "Command failed" >&2
  exit 1
}

# CORRECT - check $?
command
if (( $? != 0 )); then
  echo "Command failed" >&2
  exit 1
fi

# CORRECT - set options for safety
set -e  # Exit on error
set -u  # Exit on undefined variable
set -o pipefail  # Exit on pipe failure

---

8. Command Substitution

# CORRECT - use $() not backticks
result="$(command)"
files="$(ls -1)"

# AVOID - backticks
result=`command`  # AVOID

---

9. Arrays

# CORRECT - declare and use arrays
declare -a files
files=("file1.txt" "file2.txt" "file3.txt")

# CORRECT - append to array
files+=("file4.txt")

# CORRECT - iterate over array
for file in "${files[@]}"; do
  echo "${file}"
done

# CORRECT - array length
echo "Array has ${#files[@]} elements"

---

10. Pipes and Redirection

# CORRECT - pipe to while with process substitution
while read -r line; do
  process "${line}"
done < <(command)

# CORRECT - redirect stderr
command 2>&1 | tee log.txt

# CORRECT - redirect to file
echo "output" > file.txt
echo "append" >> file.txt

# CORRECT - here document
cat <<EOF
Line 1
Line 2
EOF

---

11. Case Statements

# CORRECT - case statement
case "${option}" in
  start)
    start_service
    ;;
  stop)
    stop_service
    ;;
  restart)
    stop_service
    start_service
    ;;
  *)
    echo "Unknown option: ${option}" >&2
    exit 1
    ;;
esac

---

12. Best Practices

# CORRECT - use set for safety
set -euo pipefail

# CORRECT - use readonly for constants
readonly CONFIG_DIR="/etc/myapp"

# CORRECT - use local for function variables
my_func() {
  local temp_file
  temp_file="$(mktemp)"
  # Use temp_file
}

# CORRECT - use shellcheck
# shellcheck disable=SC2034  # Unused variable
unused_var="value"

# CORRECT - use meaningful variable names
user_count=10  # GOOD
uc=10  # AVOID

---

Common Mistakes