shellcheck - Man Page

Shell script analysis tool

Examples (TL;DR)

tldr.sh

Synopsis

shellcheck [Options...] FILES...

Description

ShellCheck is a static analysis and linting tool for sh/bash scripts. It's mainly focused on handling typical beginner and intermediate level syntax errors and pitfalls where the shell just gives a cryptic error message or strange behavior, but it also reports on a few more advanced issues where corner cases can cause delayed failures.

ShellCheck gives shell specific advice. Consider this line:

(( area = 3.14*r*r ))

Options

-a, --check-sourced

Emit warnings in sourced files. Normally, shellcheck will only warn about issues in the specified files. With this option, any issues in sourced files will also be reported.

-C[WHEN], --color[=WHEN]

For TTY output, enable colors always, never or auto. The default is auto. --color without an argument is equivalent to --color=always.

-i CODE1[,CODE2...], --include=CODE1[,CODE2...]

Explicitly include only the specified codes in the report. Subsequent -i options are cumulative, but all the codes can be specified at once, comma-separated as a single argument. Include options override any provided exclude options.

-e CODE1[,CODE2...], --exclude=CODE1[,CODE2...]

Explicitly exclude the specified codes from the report. Subsequent -e options are cumulative, but all the codes can be specified at once, comma-separated as a single argument.

--extended-analysis=true/false

Enable/disable Dataflow Analysis to identify more issues (default true). If ShellCheck uses too much CPU/RAM when checking scripts with several thousand lines of code, extended analysis can be disabled with this flag or a directive. This flag overrides directives and rc files.

-f FORMAT, --format=FORMAT

Specify the output format of shellcheck, which prints its results in the standard output. Subsequent -f options are ignored, see Formats below for more information.

--list-optional

Output a list of known optional checks. These can be enabled with -o flags or enable directives.

--norc

Don't try to look for .shellcheckrc configuration files.

--rcfile RCFILE

Prefer the specified configuration file over searching for one in the default locations.

-o NAME1[,NAME2...], --enable=NAME1[,NAME2...]

Enable optional checks. The special name all enables all of them. Subsequent -o options accumulate. This is equivalent to specifying enable directives.

-P SOURCEPATH, --source-path=SOURCEPATH

Specify paths to search for sourced files, separated by : on Unix and ; on Windows. This is equivalent to specifying search-path directives.

-s shell, --shell=shell

Specify Bourne shell dialect. Valid values are sh, bash, dash, ksh, and busybox. The default is to deduce the shell from the file's shell directive, shebang, or .bash/.bats/.dash/.ksh extension, in that order. sh refers to POSIX sh (not the system's), and will warn of portability issues.

-S SEVERITY, --severity=severity

Specify minimum severity of errors to consider. Valid values in order of severity are error, warning, info and style. The default is style.

-V, --version

Print version information and exit.

-W NUM, --wiki-link-count=NUM

For TTY output, show NUM wiki links to more information about mentioned warnings. Set to 0 to disable them entirely.

-x, --external-sources

Follow source statements even when the file is not specified as input. By default, shellcheck will only follow files specified on the command line (plus /dev/null). This option allows following any file the script may source.

This option may also be enabled using external-sources=true in .shellcheckrc. This flag takes precedence.

FILES...

One or more script files to check, or "-" for standard input.

Formats

tty

Plain text, human readable output. This is the default.

gcc

GCC compatible output. Useful for editors that support compiling and showing syntax errors.

For example, in Vim, :set makeprg=shellcheck\ -f\ gcc\ % will allow using :make to check the script, and :cnext to jump to the next error.

<file>:<line>:<column>: <type>: <message>
checkstyle

Checkstyle compatible XML output. Supported directly or through plugins by many IDEs and build monitoring systems.

<?xml version='1.0' encoding='UTF-8'?>
<checkstyle version='4.3'>
  <file name='file'>
    <error
      line='line'
      column='column'
      severity='severity'
      message='message'
      source='ShellCheck.SC####' />
    ...
  </file>
  ...
</checkstyle>
diff

Auto-fixes in unified diff format. Can be piped to git apply or patch -p1 to automatically apply fixes.

--- a/test.sh
+++ b/test.sh
@@ -2,6 +2,6 @@
 ## Example of a broken script.
 for f in $(ls *.m3u)
 do
-  grep -qi hq.*mp3 $f \
+  grep -qi hq.*mp3 "$f" \
     && echo -e 'Playlist $f contains a HQ file in mp3 format'
 done
json1

Json is a popular serialization format that is more suitable for web applications. ShellCheck's json is compact and contains only the bare minimum. Tabs are counted as 1 character.

{
  comments: [
    {
      "file": "filename",
      "line": lineNumber,
      "column": columnNumber,
      "level": "severitylevel",
      "code": errorCode,
      "message": "warning message"
    },
    ...
  ]
}
json

This is a legacy version of the json1 format. It's a raw array of comments, and all offsets have a tab stop of 8.

quiet

Suppress all normal output. Exit with zero if no issues are found, otherwise exit with one. Stops processing after the first issue.

Directives

ShellCheck directives can be specified as comments in the shell script. If they appear before the first command, they are considered file-wide. Otherwise, they apply to the immediately following command or block:

# shellcheck key=value key=value
command-or-structure

For example, to suppress SC2035 about using ./*.jpg:

# shellcheck disable=SC2035
echo "Files: " *.jpg

To tell ShellCheck where to look for an otherwise dynamically determined file:

# shellcheck source=./lib.sh
source "$(find_install_dir)/lib.sh"

Here a shell brace group is used to suppress a warning on multiple lines:

# shellcheck disable=SC2016
{
  echo 'Modifying $PATH'
  echo 'PATH=foo:$PATH' >> ~/.bashrc
}

Valid keys are:

disable

Disables a comma separated list of error codes for the following command. The command can be a simple command like echo foo, or a compound command like a function definition, subshell block or loop. A range can be be specified with a dash, e.g. disable=SC3000-SC4000 to exclude 3xxx. All warnings can be disabled with disable=all.

enable

Enable an optional check by name, as listed with --list-optional. Only file-wide enable directives are considered.

extended-analysis

Set to true/false to enable/disable dataflow analysis. Specifying # shellcheck extended-analysis=false in particularly large (2000+ line) auto-generated scripts will reduce ShellCheck's resource usage at the expense of certain checks. Extended analysis is enabled by default.

external-sources

Set to true in .shellcheckrc to always allow ShellCheck to open arbitrary files from 'source' statements (the way most tools do).

This option defaults to false only due to ShellCheck's origin as a remote service for checking untrusted scripts. It can safely be enabled for normal development.

source

Overrides the filename included by a source/. statement. This can be used to tell shellcheck where to look for a file whose name is determined at runtime, or to skip a source by telling it to use /dev/null.

source-path

Add a directory to the search path for source/. statements (by default, only ShellCheck's working directory is included). Absolute paths will also be rooted in these paths. The special path SCRIPTDIR can be used to specify the currently checked script's directory, as in source-path=SCRIPTDIR or source-path=SCRIPTDIR/../libs. Multiple paths accumulate, and -P takes precedence over them.

shell

Overrides the shell detected from the shebang. This is useful for files meant to be included (and thus lacking a shebang), or possibly as a more targeted alternative to 'disable=SC2039'.

RC Files

Unless --norc is used, ShellCheck will look for a file .shellcheckrc or shellcheckrc in the script's directory and each parent directory. If found, it will read key=value pairs from it and treat them as file-wide directives.

Here is an example .shellcheckrc:

# Look for 'source'd files relative to the checked script,
# and also look for absolute paths in /mnt/chroot
source-path=SCRIPTDIR
source-path=/mnt/chroot

# Since 0.9.0, values can be quoted with '' or "" to allow spaces
source-path="My Documents/scripts"

# Allow opening any 'source'd file, even if not specified as input
external-sources=true

# Turn on warnings for unquoted variables with safe values
enable=quote-safe-variables

# Turn on warnings for unassigned uppercase variables
enable=check-unassigned-uppercase

# Allow [ ! -z foo ] instead of suggesting -n
disable=SC2236

If no .shellcheckrc is found in any of the parent directories, ShellCheck will look in ~/.shellcheckrc followed by the XDG config directory (usually ~/.config/shellcheckrc) on Unix, or %APPDATA%/shellcheckrc on Windows. Only the first file found will be used.

Note for Snap users: the Snap sandbox disallows access to hidden files. Use shellcheckrc without the dot instead.

Note for Docker users: ShellCheck will only be able to look for files that are mounted in the container, so ~/.shellcheckrc will not be read.

Environment Variables

The environment variable SHELLCHECK_OPTS can be set with default flags:

export SHELLCHECK_OPTS='--shell=bash --exclude=SC2016'

Its value will be split on spaces and prepended to the command line on each invocation.

Return Values

ShellCheck uses the following exit codes:

Locale

This version of ShellCheck is only available in English. All files are leniently decoded as UTF-8, with a fallback of ISO-8859-1 for invalid sequences. LC_CTYPE is respected for output, and defaults to UTF-8 for locales where encoding is unspecified (such as the C locale).

Windows users seeing commitBuffer: invalid argument (invalid character) should set their terminal to use UTF-8 with chcp 65001.

Known Incompatibilities

(If nothing in this section makes sense, you are unlikely to be affected by it)

To avoid confusing and misguided suggestions, ShellCheck requires function bodies to be either { brace groups; } or ( subshells ), and function names containing []*=! are only recognized after a function keyword.

The following unconventional function definitions are identical in Bash, but ShellCheck only recognizes the latter.

[x!=y] () [[ $1 ]]
function [x!=y] () { [[ $1 ]]; }

Shells without the function keyword do not allow these characters in function names to begin with. Function names containing {} are not supported at all.

Further, if ShellCheck sees [x!=y] it will assume this is an invalid comparison. To invoke the above function, quote the command as in '[x!=y]', or to retain the same globbing behavior, use command [x!=y].

ShellCheck imposes additional restrictions on the [ command to help diagnose common invalid uses. While [ $x= 1 ] is defined in POSIX, ShellCheck will assume it was intended as the much more likely comparison [ "$x" = 1 ] and fail accordingly. For unconventional or dynamic uses of the [ command, use test or \[ instead.

Reporting Bugs

Bugs and issues can be reported on GitHub:

https://github.com/koalaman/shellcheck/issues

Authors

ShellCheck is developed and maintained by Vidar Holen, with assistance from a long list of wonderful contributors.

See Also

sh(1) bash(1)

Info

Shell script analysis tool