Ubuntu Manpage: shellcheck - Shell script analysis tool

NAME

       shellcheck - Shell script analysis tool

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 ))

       • For scripts starting with #!/bin/sh (or when using -s sh), ShellCheck will warn that  ((
         .. )) is not POSIX compliant (similar to checkbashisms).

       • For  scripts  starting  with  #!/bin/bash  (or using -s bash), ShellCheck will warn that
         decimals are not supported.

       • For scripts starting with #!/bin/ksh (or using -s ksh), ShellCheck will not warn at all,
         as ksh supports decimals in arithmetic contexts.

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.

-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.

-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 and ksh. 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.

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

# 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:

       • 0: All files successfully scanned with no issues.

       • 1: All files successfully scanned with some issues.

       • 2: Some files could not be processed (e.g.  file not found).

       • 3: ShellCheck was invoked with bad syntax (e.g.  unknown flag).

       • 4: ShellCheck was invoked with bad options (e.g.  unknown formatter).

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.

COPYRIGHT

       Copyright 2012-2021, Vidar Holen and contributors.  Licensed under the GNU General  Public
       License version 3 or later, see https://gnu.org/licenses/gpl.html