Quick Answer
ShellCheck analyzes bash scripts for mistakes that work on happy-path input but fail on edge cases — unquoted variables, unreachable commands, deprecated syntax, and pipelines that hide errors. An unquoted `$var` splits on whitespace and expands globs, breaking filenames with spaces. Reading the raw rule text means context switching between the error code, the wiki, and your editor. This decoder accepts any SC code such as SC2086 and returns the rule name, a plain-English explanation of what is wrong, why it matters in production, and a before/after example showing the fix. Click Copy Fix to paste the corrected line directly. Lookup runs client-side with no login. Fixing warnings before deploy prevents the exact failures ShellCheck was designed to catch — silent breakage on unexpected input. A warning-free script still needs the operational layer around it — strict mode, an ERR trap, lock, timeout and cleanup — packaged as bashlib.sh and template.sh in The Production Bash Toolkit at /starter-kit.
What is ShellCheck?
ShellCheck is an open-source static analysis tool for bash and sh scripts. It detects common mistakes — unquoted variables, incorrect conditionals, portability issues, and deprecated syntax — before they cause failures in production. It is available as a CLI tool and integrates with most editors.
How do I run ShellCheck on my script?
Install ShellCheck with `apt install shellcheck` on Debian/Ubuntu or `brew install shellcheck` on macOS. Then run `shellcheck script.sh`. For CI pipelines, ShellCheck exits non-zero if any warnings are found, making it easy to enforce as a gate.
What does ShellCheck SC2086 mean?
SC2086 warns that a variable is not double-quoted, which exposes it to word splitting and glob expansion. `echo $var` should be `echo "$var"`. If $var contains spaces or special characters, the unquoted version breaks silently in ways that are hard to debug.
Why does ShellCheck flag my script if it works fine?
ShellCheck warns about patterns that work in normal cases but fail in edge cases — variables with spaces, filenames with special characters, or pipelines that swallow errors. Each warning is a real bug risk. The script appears to work until it encounters unexpected input.
6 scripts + shared library + 52-page field guide. The production layer the free snippets don't cover.
Get the Toolkit →Ten functions I source into every script on my own boxes — strict-mode setup, an ERR trap that names the failing line, lock and timeout wrappers, and cleanup that runs on every exit path. One email, no sequence.
Accepts SC codes, numbers, or pasted ShellCheck messages
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