shellcheck v0.9 release: static analysis tool for shell scripts

by do son · Published July 28, 2019 · Updated December 13, 2022

ShellCheck – A shell script static analysis tool

The goals of ShellCheck are

To point out and clarify typical beginner’s syntax issues that cause a shell to give cryptic error messages.
To point out and clarify typical intermediate-level semantic problems that cause a shell to behave strangely and counter-intuitively.
To point out subtle caveats, corner cases, and pitfalls that may cause an advanced user’s otherwise working script to fail under future circumstances.

Changelog v0.9

Added

SC2316: Warn about ‘local readonly foo’ and similar (thanks, patrickxia!)
SC2317: Warn about unreachable commands
SC2318: Warn about backreferences in ‘declare x=1 y=$x’
SC2319/SC2320: Warn when $? refers to echo/printf/[ ]/[[ ]]/test
SC2321: Suggest removing ((..))inarray[((idx))]=val
SC2322: Suggest collapsing double parentheses in arithmetic contexts
SC2323: Suggest removing wrapping parentheses in a[(x+1)]=val

Fixed

SC2086: Now uses DFA to make more accurate predictions about values
SC2086: No longer warns about values declared as integer with declare -i

Changed

ShellCheck now has a Data Flow Analysis engine to make smarter decisions based on control flow rather than just syntax. Existing checks will gradually start using it, which may cause them to trigger differently (but more accurately).
Values in directives/shellcheckrc can now be quoted with ” or “”

Installing

On Debian based distros:

apt-get install shellcheck

On Arch Linux based distros:

pacman -S shellcheck

Use

On the web

Paste a shell script on https://www.shellcheck.net for instant feedback.

From your terminal

Run shellcheck yourscript in your terminal for instant output, as seen above.

In your editor

You can see ShellCheck suggestions directly in a variety of editors.

Vim, through ALE, Neomake, or Syntastic:

Emacs, through Flycheck:

Sublime, through SublimeLinter.
Atom, through Linter.
VSCode, through vscode-shellcheck.
Most other editors, through GCC error compatibility.

In your build or test suites

While ShellCheck is mostly intended for interactive use, it can easily be added to builds or test suites.

It makes canonical use of exit codes and can output simple JSON, CheckStyle compatible XML, GCC compatible warnings as well as human-readable text (with or without ANSI colors).