Shellcheck

ShellCheck - Shell Script Static Analysis

Auto-routes when user mentions shellcheck, shell linting, bash script analysis, or SC error codes.

Overview

ShellCheck is a GPLv3-licensed static analysis tool that identifies bugs in bash/sh shell scripts. It detects:

• Syntax errors and parsing issues
• Semantic problems causing unexpected behavior
• Quoting issues and word splitting bugs
• POSIX compatibility warnings
• Style and best practice violations

Voice Notification

When executing a workflow, do BOTH:

1. Send voice notification:

   curl -s -X POST http://localhost:8888/notify \
     -H "Content-Type: application/json" \
     -d '{"message": "Running the WORKFLOWNAME workflow from the ShellCheck skill"}' \
     > /dev/null 2>&1 &
   

2. Output text notification:

   Running the **WorkflowName** workflow from the **ShellCheck** skill...
   

Workflow Routing

Workflow	Trigger	File
Analyze	"shellcheck this", "lint script", "check shell"	Workflows/Analyze.md
Fix	"fix shell errors", "apply shellcheck fixes"	Workflows/Fix.md
Setup	"setup shellcheck", "configure shellcheck"	Workflows/Setup.md
Explain	"explain SC2086", "what is SC code"	Workflows/Explain.md

Quick Reference

Basic Usage

# Check a script
shellcheck myscript.sh

# Specify shell dialect
shellcheck -s bash myscript.sh

# Exclude specific codes
shellcheck -e SC2086,SC2046 myscript.sh

# Output formats
shellcheck -f gcc myscript.sh      # Editor integration
shellcheck -f json myscript.sh     # Machine readable
shellcheck -f diff myscript.sh     # Auto-fix patches

Common SC Codes

Code	Issue	Fix
SC2086	Unquoted variable	"$var"
SC2046	Unquoted command substitution	"$(cmd)"
SC2034	Unused variable	Remove or export
SC2154	Unassigned variable	Assign or disable
SC2155	Declare and assign separately	Split declaration

Inline Directives

# Disable for next command
# shellcheck disable=SC2086
echo $var

# Disable for entire file (after shebang)
#!/bin/bash
# shellcheck disable=SC2086,SC2046

Full Documentation

• Error Codes: SkillSearch('shellcheck error codes') -> loads ErrorCodes.md
• Configuration: SkillSearch('shellcheck config') -> loads Configuration.md
• CI/CD Integration: SkillSearch('shellcheck ci') -> loads Integration.md
• Best Practices: SkillSearch('shellcheck practices') -> loads BestPractices.md

Examples

Example 1: Analyze a script

User: "shellcheck my deploy script"
-> Invokes Analyze workflow
-> Runs shellcheck with JSON output
-> Presents findings grouped by severity
-> Suggests fixes with wiki links

Example 2: Fix common issues

User: "fix the shellcheck errors in scripts/"
-> Invokes Fix workflow
-> Generates diff output
-> Applies fixes interactively
-> Re-runs validation

Example 3: Setup for project

User: "setup shellcheck for this repo"
-> Invokes Setup workflow
-> Creates .shellcheckrc
-> Adds pre-commit hook
-> Configures CI workflow

Example 4: Explain an error code

User: "what does SC2086 mean?"
-> Invokes Explain workflow
-> Fetches wiki documentation
-> Shows examples and fixes
-> Provides context-specific guidance

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Gotchas

• SC2086 is wrong inside [[ ]]: Bash's [[ ]] does not word-split, so [[ -n $var ]] is safe unquoted. Disabling SC2086 on [[ ]] blocks is a sign you're applying the lint to the wrong construct, not a sign the rule is broken.
• SC2034 fires on indirectly-used variables: Variables consumed via ${!prefix*} indirection, declare -p introspection, or sourced into another script trigger "unused" false positives. Use # shellcheck disable=SC2034 with a comment explaining the indirection — don't silence globally.
• Shebang determines the dialect, not the filename: script.sh with #!/bin/sh is checked as POSIX sh and rejects bashisms like [[ ]] or arrays. Either set the correct shebang or pass -s bash explicitly; never rely on the .sh extension.
• shellcheck -e SC2086,SC2046 in .shellcheckrc hides real bugs: Project-wide disables compound — a year later nobody remembers why and unquoted expansions ship to prod. Prefer inline disables with a justification comment over global suppression.
• Source-following requires -x flag: source ./lib.sh is not analyzed by default. Run with shellcheck -x script.sh for full coverage, or add # shellcheck source=./lib.sh directives. CI configs frequently miss this and ship un-linted sourced files.
• -f diff patches assume the script parses cleanly: Syntax errors prevent the auto-fix output entirely, with no clear message. If -f diff produces nothing, run without -f first and fix parse errors before re-running for patches.