[![Build Status](https://travis-ci.org/koalaman/shellcheck.svg?branch=master)](https://travis-ci.org/koalaman/shellcheck) # ShellCheck - A shell script static analysis tool ShellCheck is a GPLv3 tool that gives warnings and suggestions for bash/sh shell scripts: ![Screenshot of a terminal showing problematic shell script lines highlighted](doc/terminal.png) 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. See [the gallery of bad code](README.md#user-content-gallery-of-bad-code) for examples of what ShellCheck can help you identify! ## Table of Contents - [How to use](#how-to-use) - [On the web](#on-the-web) - [From your terminal](#from-your-terminal) - [In your editor](#in-your-editor) - [In your build or test suites](#in-your-build-or-test-suites) - [Installing](#installing) - [Travis CI](#travis-ci) - [Compiling from source](#compiling-from-source) - [Installing Cabal](#installing-cabal) - [Compiling ShellCheck](#compiling-shellcheck) - [Running tests](#running-tests) - [Gallery of bad code](#gallery-of-bad-code) - [Quoting](#quoting) - [Conditionals](#conditionals) - [Frequently misused commands](#frequently-misused-commands) - [Common beginner's mistakes](#common-beginners-mistakes) - [Style](#style) - [Data and typing errors](#data-and-typing-errors) - [Robustness](#robustness) - [Portability](#portability) - [Miscellaneous](#miscellaneous) - [Testimonials](#testimonials) - [Ignoring issues](#ignoring-issues) - [Reporting bugs](#reporting-bugs) - [Contributing](#contributing) - [Copyright](#copyright) ## How to use There are a number of ways to use ShellCheck! ### On the web Paste a shell script on https://www.shellcheck.net for instant feedback. [ShellCheck.net](https://www.shellcheck.net) is always synchronized to the latest git commit, and is the easiest way to give ShellCheck a go. Tell your friends! ### 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](https://github.com/w0rp/ale), [Neomake](https://github.com/neomake/neomake), or [Syntastic](https://github.com/scrooloose/syntastic): ![Screenshot of Vim showing inlined shellcheck feedback](doc/vim-syntastic.png). * Emacs, through [Flycheck](https://github.com/flycheck/flycheck) or [Flymake](https://github.com/federicotdn/flymake-shellcheck): ![Screenshot of emacs showing inlined shellcheck feedback](doc/emacs-flycheck.png). * Sublime, through [SublimeLinter](https://github.com/SublimeLinter/SublimeLinter-shellcheck). * Atom, through [Linter](https://github.com/AtomLinter/linter-shellcheck). * VSCode, through [vscode-shellcheck](https://github.com/timonwong/vscode-shellcheck). * Most other editors, through [GCC error compatibility](shellcheck.1.md#user-content-formats). ### In your build or test suites While ShellCheck is mostly intended for interactive use, it can easily be added to builds or test suites. ShellCheck 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). See the [Integration](https://github.com/koalaman/shellcheck/wiki/Integration) wiki page for more documentation. ## Installing The easiest way to install ShellCheck locally is through your package manager. On systems with Cabal (installs to `~/.cabal/bin`): cabal update cabal install ShellCheck On systems with Stack (installs to `~/.local/bin`): stack update stack install ShellCheck On Debian based distros: apt-get install shellcheck On Arch Linux based distros: pacman -S shellcheck or get the dependency free [shellcheck-static](https://aur.archlinux.org/packages/shellcheck-static/) from the AUR. On Gentoo based distros: emerge --ask shellcheck On EPEL based distros: yum -y install epel-release yum install ShellCheck On Fedora based distros: dnf install ShellCheck On FreeBSD: pkg install hs-ShellCheck On OS X with homebrew: brew install shellcheck On OpenBSD: pkg_add shellcheck On openSUSE zypper in ShellCheck Or use OneClickInstall - https://software.opensuse.org/package/ShellCheck On Solus: eopkg install shellcheck On Windows (via [scoop](http://scoop.sh)): scoop install shellcheck From Snap Store: snap install --channel=edge shellcheck From Docker Hub: ```sh docker pull koalaman/shellcheck:stable # Or :v0.4.7 for that version, or :latest for daily builds docker run -v "$PWD:/mnt" koalaman/shellcheck myscript ``` or use `koalaman/shellcheck-alpine` if you want a larger Alpine Linux based image to extend. It works exactly like a regular Alpine image, but has shellcheck preinstalled. Alternatively, you can download pre-compiled binaries for the latest release here: * [Linux, x86_64](https://storage.googleapis.com/shellcheck/shellcheck-stable.linux.x86_64.tar.xz) (statically linked) * [Linux, armv6hf](https://storage.googleapis.com/shellcheck/shellcheck-stable.linux.armv6hf.tar.xz), i.e. Raspberry Pi (statically linked) * [Windows, x86](https://storage.googleapis.com/shellcheck/shellcheck-stable.zip) or see the [storage bucket listing](https://shellcheck.storage.googleapis.com/index.html) for checksums, older versions and the latest daily builds. Distro packages already come with a `man` page. If you are building from source, it can be installed with: pandoc -s -t man shellcheck.1.md -o shellcheck.1 sudo mv shellcheck.1 /usr/share/man/man1 ## Travis CI Travis CI has now integrated ShellCheck by default, so you don't need to manually install it. If you still want to do so in order to upgrade at your leisure or ensure the latest release, follow the steps to install the shellcheck binary, bellow. ## Installing the shellcheck binary *Pre-requisite*: the program 'xz' needs to be installed on the system. To install it on debian/ubuntu/linux mint, run `apt install xz-utils`. To install it on Redhat/Fedora/CentOS, run `yum -y install xz`. ```bash export scversion="stable" # or "v0.4.7", or "latest" wget "https://storage.googleapis.com/shellcheck/shellcheck-${scversion}.linux.x86_64.tar.xz" tar --xz -xvf shellcheck-"${scversion}".linux.x86_64.tar.xz cp shellcheck-"${scversion}"/shellcheck /usr/bin/ shellcheck --version ``` ## Compiling from source This section describes how to build ShellCheck from a source directory. ShellCheck is written in Haskell and requires 2GB of RAM to compile. ### Installing Cabal ShellCheck is built and packaged using Cabal. Install the package `cabal-install` from your system's package manager (with e.g. `apt-get`, `brew`, `emerge`, `yum`, or `zypper`). On MacOS (OS X), you can do a fast install of Cabal using brew, which takes a couple of minutes instead of more than 30 minutes if you try to compile it from source. brew install cask brew cask install haskell-platform cabal install cabal-install On MacPorts, the package is instead called `hs-cabal-install`, while native Windows users should install the latest version of the Haskell platform from https://www.haskell.org/platform/ Verify that `cabal` is installed and update its dependency list with $ cabal update ### Compiling ShellCheck `git clone` this repository, and `cd` to the ShellCheck source directory to build/install: $ cabal install Or if you intend to run the tests: $ cabal install --enable-tests This will compile ShellCheck and install it to your `~/.cabal/bin` directory. Add this directory to your `PATH` (for bash, add this to your `~/.bashrc`): ```sh export PATH="$HOME/.cabal/bin:$PATH" ``` Log out and in again, and verify that your PATH is set up correctly: ```sh $ which shellcheck ~/.cabal/bin/shellcheck ``` On native Windows, the `PATH` should already be set up, but the system may use a legacy codepage. In `cmd.exe`, `powershell.exe` and Powershell ISE, make sure to use a TrueType font, not a Raster font, and set the active codepage to UTF-8 (65001) with `chcp`: > chcp 65001 Active code page: 65001 In Powershell ISE, you may need to additionally update the output encoding: > [Console]::OutputEncoding = [System.Text.Encoding]::UTF8 ### Running tests To run the unit test suite: $ cabal test ## Gallery of bad code So what kind of things does ShellCheck look for? Here is an incomplete list of detected issues. ### Quoting ShellCheck can recognize several types of incorrect quoting: ```sh echo $1 # Unquoted variables find . -name *.ogg # Unquoted find/grep patterns rm "~/my file.txt" # Quoted tilde expansion v='--verbose="true"'; cmd $v # Literal quotes in variables for f in "*.ogg" # Incorrectly quoted 'for' loops touch $@ # Unquoted $@ echo 'Don't forget to restart!' # Singlequote closed by apostrophe echo 'Don\'t try this at home' # Attempting to escape ' in '' echo 'Path is $PATH' # Variables in single quotes trap "echo Took ${SECONDS}s" 0 # Prematurely expanded trap ``` ### Conditionals ShellCheck can recognize many types of incorrect test statements. ```sh [[ n != 0 ]] # Constant test expressions [[ -e *.mpg ]] # Existence checks of globs [[ $foo==0 ]] # Always true due to missing spaces [[ -n "$foo " ]] # Always true due to literals [[ $foo =~ "fo+" ]] # Quoted regex in =~ [ foo =~ re ] # Unsupported [ ] operators [ $1 -eq "shellcheck" ] # Numerical comparison of strings [ $n && $m ] # && in [ .. ] [ grep -q foo file ] # Command without $(..) [[ "$$file" == *.jpg ]] # Comparisons that can't succeed (( 1 -lt 2 )) # Using test operators in ((..)) ``` ### Frequently misused commands ShellCheck can recognize instances where commands are used incorrectly: ```sh grep '*foo*' file # Globs in regex contexts find . -exec foo {} && bar {} \; # Prematurely terminated find -exec sudo echo 'Var=42' > /etc/profile # Redirecting sudo time --format=%s sleep 10 # Passing time(1) flags to time builtin while read h; do ssh "$h" uptime # Commands eating while loop input alias archive='mv $1 /backup' # Defining aliases with arguments tr -cd '[a-zA-Z0-9]' # [] around ranges in tr exec foo; echo "Done!" # Misused 'exec' find -name \*.bak -o -name \*~ -delete # Implicit precedence in find # find . -exec foo > bar \; # Redirections in find f() { whoami; }; sudo f # External use of internal functions ``` ### Common beginner's mistakes ShellCheck recognizes many common beginner's syntax errors: ```sh var = 42 # Spaces around = in assignments $foo=42 # $ in assignments for $var in *; do ... # $ in for loop variables var$n="Hello" # Wrong indirect assignment echo ${var$n} # Wrong indirect reference var=(1, 2, 3) # Comma separated arrays array=( [index] = value ) # Incorrect index initialization echo $var[14] # Missing {} in array references echo "Argument 10 is $10" # Positional parameter misreference if $(myfunction); then ..; fi # Wrapping commands in $() else if othercondition; then .. # Using 'else if' f; f() { echo "hello world; } # Using function before definition [ false ] # 'false' being true if ( -f file ) # Using (..) instead of test ``` ### Style ShellCheck can make suggestions to improve style: ```sh [[ -z $(find /tmp | grep mpg) ]] # Use grep -q instead a >> log; b >> log; c >> log # Use a redirection block instead echo "The time is `date`" # Use $() instead cd dir; process *; cd ..; # Use subshells instead echo $[1+2] # Use standard $((..)) instead of old $[] echo $(($RANDOM % 6)) # Don't use $ on variables in $((..)) echo "$(date)" # Useless use of echo cat file | grep foo # Useless use of cat ``` ### Data and typing errors ShellCheck can recognize issues related to data and typing: ```sh args="$@" # Assigning arrays to strings files=(foo bar); echo "$files" # Referencing arrays as strings declare -A arr=(foo bar) # Associative arrays without index printf "%s\n" "Arguments: $@." # Concatenating strings and arrays [[ $# > 2 ]] # Comparing numbers as strings var=World; echo "Hello " var # Unused lowercase variables echo "Hello $name" # Unassigned lowercase variables cmd | read bar; echo $bar # Assignments in subshells cat foo | cp bar # Piping to commands that don't read printf '%s: %s\n' foo # Mismatches in printf argument count ``` ### Robustness ShellCheck can make suggestions for improving the robustness of a script: ```sh rm -rf "$STEAMROOT/"* # Catastrophic rm touch ./-l; ls * # Globs that could become options find . -exec sh -c 'a && b {}' \; # Find -exec shell injection printf "Hello $name" # Variables in printf format for f in $(ls *.txt); do # Iterating over ls output export MYVAR=$(cmd) # Masked exit codes case $version in 2.*) :;; 2.6.*) # Shadowed case branches ``` ### Portability ShellCheck will warn when using features not supported by the shebang. For example, if you set the shebang to `#!/bin/sh`, ShellCheck will warn about portability issues similar to `checkbashisms`: ```sh echo {1..$n} # Works in ksh, but not bash/dash/sh echo {1..10} # Works in ksh and bash, but not dash/sh echo -n 42 # Works in ksh, bash and dash, undefined in sh trap 'exit 42' sigint # Unportable signal spec cmd &> file # Unportable redirection operator read foo < /dev/tcp/host/22 # Unportable intercepted files foo-bar() { ..; } # Undefined/unsupported function name [ $UID = 0 ] # Variable undefined in dash/sh local var=value # local is undefined in sh time sleep 1 | sleep 5 # Undefined uses of 'time' ``` ### Miscellaneous ShellCheck recognizes a menagerie of other issues: ```sh PS1='\e[0;32m\$\e[0m ' # PS1 colors not in \[..\] PATH="$PATH:~/bin" # Literal tilde in $PATH rm “file” # Unicode quotes echo "Hello world" # Carriage return / DOS line endings echo hello \ # Trailing spaces after \ var=42 echo $var # Expansion of inlined environment #!/bin/bash -x -e # Common shebang errors echo $((n/180*100)) # Unnecessary loss of precision ls *[:digit:].txt # Bad character class globs sed 's/foo/bar/' file > file # Redirecting to input while getopts "a" f; do case $f in "b") # Unhandled getopts flags ``` ## Testimonials > At first you're like "shellcheck is awesome" but then you're like "wtf are we still using bash" Alexander Tarasikov, [via Twitter](https://twitter.com/astarasikov/status/568825996532707330) ## Ignoring issues Issues can be ignored via environmental variable, command line, individually or globally within a file: https://github.com/koalaman/shellcheck/wiki/Ignore ## Reporting bugs Please use the GitHub issue tracker for any bugs or feature suggestions: https://github.com/koalaman/shellcheck/issues ## Contributing Please submit patches to code or documentation as GitHub pull requests! Check out the [DevGuide](https://github.com/koalaman/shellcheck/wiki/DevGuide) on the ShellCheck Wiki. Contributions must be licensed under the GNU GPLv3. The contributor retains the copyright. ## Copyright ShellCheck is licensed under the GNU General Public License, v3. A copy of this license is included in the file [LICENSE](LICENSE). Copyright 2012-2018, Vidar 'koala_man' Holen and contributors. Happy ShellChecking! ## Other Resources * The wiki has [long form descriptions](https://github.com/koalaman/shellcheck/wiki/Checks) for each warning, e.g. [SC2221](https://github.com/koalaman/shellcheck/wiki/SC2221). * ShellCheck does not attempt to enforce any kind of formatting or indenting style, so also check out [shfmt](https://github.com/mvdan/sh)!