Shellcheck Configuration

# shellcheck-configuration — detailed patterns and worked examples

## ShellCheck Fundamentals

### What is ShellCheck?

ShellCheck is a static analysis tool that analyzes shell scripts and detects problematic patterns. It supports:

- Bash, sh, dash, ksh, and other POSIX shells
- Over 100 different warnings and errors
- Configuration for target shell and flags
- Integration with editors and CI/CD systems

### Installation

```bash
# macOS with Homebrew
brew install shellcheck

# Ubuntu/Debian
apt-get install shellcheck

# From source
git clone https://github.com/koalaman/shellcheck.git
cd shellcheck
make build
make install

# Verify installation
shellcheck --version
```

## Configuration Files

### .shellcheckrc (Project Level)

Create `.shellcheckrc` in your project root:

```
# Specify target shell
shell=bash

# Enable optional checks
enable=avoid-nullary-conditions
enable=require-variable-braces

# Disable specific warnings
disable=SC1091
disable=SC2086
```

### Environment Variables

```bash
# Set default shell target
export SHELLCHECK_SHELL=bash

# Enable strict mode
export SHELLCHECK_STRICT=true

# Specify configuration file location
export SHELLCHECK_CONFIG=~/.shellcheckrc
```

## Common ShellCheck Error Codes

### SC1000-1099: Parser Errors

```bash
# SC1004: Backslash continuation not followed by newline
echo hello\
world  # Error - needs line continuation

# SC1008: Invalid data for operator `=='
if [[ $var =  "value" ]]; then  # Space before ==
    true
fi
```

### SC2000-2099: Shell Issues

```bash
# SC2009: Consider using pgrep or pidof instead of grep|grep
ps aux | grep -v grep | grep myprocess  # Use pgrep instead

# SC2012: Use `ls` only for viewing. Use `find` for reliable output
for file in $(ls -la)  # Better: use find or globbing

# SC2015: Avoid using && and || instead of if-then-else
[[ -f "$file" ]] && echo "found" || echo "not found"  # Less clear

# SC2016: Expressions don't expand in single quotes
echo '$VAR'  # Literal $VAR, not variable expansion

# SC2026: This word is non-standard. Set POSIXLY_CORRECT
# when using with scripts for other shells
```

### SC2100-2199: Quoting Issues

```bash
# SC2086: Double quote to prevent globbing and word splitting
for i in $list; do  # Should be: for i in $list or for i in "$list"
    echo "$i"
done

# SC2115: Literal tilde in path not expanded. Use $HOME instead
~/.bashrc  # In strings, use "$HOME/.bashrc"

# SC2181: Check exit code directly with `if`, not indirectly in a list
some_command
if [ $? -eq 0 ]; then  # Better: if some_command; then

# SC2206: Quote to prevent word splitting or set IFS
array=( $items )  # Should use: array=( $items )
```

### SC3000-3999: POSIX Compliance Issues

```bash
# SC3010: In POSIX sh, use 'case' instead of 'cond && foo'
[[ $var == "value" ]] && do_something  # Not POSIX

# SC3043: In POSIX sh, use 'local' is undefined
function my_func() {
    local var=value  # Not POSIX in some shells
}
```

## Practical Configuration Examples

### Minimal Configuration (Strict POSIX)

```bash
#!/bin/bash
# Configure for maximum portability

shellcheck \
  --shell=sh \
  --external-sources \
  --check-sourced \
  script.sh
```

### Development Configuration (Bash with Relaxed Rules)

```bash
#!/bin/bash
# Configure for Bash development

shellcheck \
  --shell=bash \
  --exclude=SC1091,SC2119 \
  --enable=all \
  script.sh
```

### CI/CD Integration Configuration

```bash
#!/bin/bash
set -Eeuo pipefail

# Analyze all shell scripts and fail on issues
find . -type f -name "*.sh" | while read -r script; do
    echo "Checking: $script"
    shellcheck \
        --shell=bash \
        --format=gcc \
        --exclude=SC1091 \
        "$script" || exit 1
done
```

### .shellcheckrc for Project

```
# Shell dialect to analyze against
shell=bash

# Enable optional checks
enable=avoid-nullary-conditions,require-variable-braces,check-unassigned-uppercase

# Disable specific warnings
# SC1091: Not following sourced files (many false positives)
disable=