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Double quote to prevent globbing and word splitting. Open
exec ${RAILS} runner $(readlink -f $(dirname $0))/3scale $*
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Double quote to prevent globbing and word splitting.
Problematic code:
echo $1
for i in $*; do :; done # this done and the next one also applies to expanding arrays.
for i in $@; do :; done
Correct code:
echo "$1"
for i in "$@"; do :; done # or, 'for i; do'
Rationale
The first code looks like "print the first argument". It's actually "Split the first argument by IFS (spaces, tabs and line feeds). Expand each of them as if it was a glob. Join all the resulting strings and filenames with spaces. Print the result."
The second one looks like "iterate through all arguments". It's actually "join all the arguments by the first character of IFS (space), split them by IFS and expand each of them as globs, and iterate on the resulting list". The third one skips the joining part.
Quoting variables prevents word splitting and glob expansion, and prevents the script from breaking when input contains spaces, line feeds, glob characters and such.
Strictly speaking, only expansions themselves need to be quoted, but for stylistic reasons, entire arguments with multiple variable and literal parts are often quoted as one:
$HOME/$dir/dist/bin/$file # Unquoted (bad)
"$HOME"/"$dir"/dist/bin/"$file" # Minimal quoting (good)
"$HOME/$dir/dist/bin/$file" # Canonical quoting (good)
When quoting composite arguments, make sure to exclude globs and brace expansions, which lose their special meaning in double quotes: "$HOME/$dir/src/*.c"
will not expand, but "$HOME/$dir/src"/*.c
will.
Note that $( )
starts a new context, and variables in it have to be quoted independently:
echo "This $variable is quoted $(but this $variable is not)"
echo "This $variable is quoted $(and now this "$variable" is too)"
Exceptions
Sometimes you want to split on spaces, like when building a command line:
options="-j 5 -B"
make $options file
Just quoting this doesn't work. Instead, you should have used an array (bash, ksh, zsh):
options=(-j 5 -B) # ksh: set -A options -- -j 5 -B
make "${options[@]}" file
or a function (POSIX):
make_with_flags() { make -j 5 -B "$@"; }
make_with_flags file
To split on spaces but not perform glob expansion, Posix has a set -f
to disable globbing. You can disable word splitting by setting IFS=''
.
Similarly, you might want an optional argument:
debug=""
[[ $1 == "--trace-commands" ]] && debug="-x"
bash $debug script
Quoting this doesn't work, since in the default case, "$debug"
would expand to one empty argument while $debug
would expand into zero arguments. In this case, you can use an array with zero or one elements as outlined above, or you can use an unquoted expansion with an alternate value:
debug=""
[[ $1 == "--trace-commands" ]] && debug="yes"
bash ${debug:+"-x"} script
This is better than an unquoted value because the alternative value can be properly quoted, e.g. wget ${output:+ -o "$output"}
.
As always, this warning can be [[ignore]]d on a case-by-case basis.
this is especially relevant when BASH many not be available for the array work around. For example, use in eval or in command options where script has total control of the variables...
FLAGS="-av -e 'ssh -x' --delete --delete-excluded"
...
# shellcheck disable=SC2086
eval rsync $FLAGS ~/dir remote_host:dir
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Double quote to prevent globbing and word splitting. Open
exec ${RAILS} runner $(readlink -f $(dirname $0))/3scale $*
- Read upRead up
- Exclude checks
Double quote to prevent globbing and word splitting.
Problematic code:
echo $1
for i in $*; do :; done # this done and the next one also applies to expanding arrays.
for i in $@; do :; done
Correct code:
echo "$1"
for i in "$@"; do :; done # or, 'for i; do'
Rationale
The first code looks like "print the first argument". It's actually "Split the first argument by IFS (spaces, tabs and line feeds). Expand each of them as if it was a glob. Join all the resulting strings and filenames with spaces. Print the result."
The second one looks like "iterate through all arguments". It's actually "join all the arguments by the first character of IFS (space), split them by IFS and expand each of them as globs, and iterate on the resulting list". The third one skips the joining part.
Quoting variables prevents word splitting and glob expansion, and prevents the script from breaking when input contains spaces, line feeds, glob characters and such.
Strictly speaking, only expansions themselves need to be quoted, but for stylistic reasons, entire arguments with multiple variable and literal parts are often quoted as one:
$HOME/$dir/dist/bin/$file # Unquoted (bad)
"$HOME"/"$dir"/dist/bin/"$file" # Minimal quoting (good)
"$HOME/$dir/dist/bin/$file" # Canonical quoting (good)
When quoting composite arguments, make sure to exclude globs and brace expansions, which lose their special meaning in double quotes: "$HOME/$dir/src/*.c"
will not expand, but "$HOME/$dir/src"/*.c
will.
Note that $( )
starts a new context, and variables in it have to be quoted independently:
echo "This $variable is quoted $(but this $variable is not)"
echo "This $variable is quoted $(and now this "$variable" is too)"
Exceptions
Sometimes you want to split on spaces, like when building a command line:
options="-j 5 -B"
make $options file
Just quoting this doesn't work. Instead, you should have used an array (bash, ksh, zsh):
options=(-j 5 -B) # ksh: set -A options -- -j 5 -B
make "${options[@]}" file
or a function (POSIX):
make_with_flags() { make -j 5 -B "$@"; }
make_with_flags file
To split on spaces but not perform glob expansion, Posix has a set -f
to disable globbing. You can disable word splitting by setting IFS=''
.
Similarly, you might want an optional argument:
debug=""
[[ $1 == "--trace-commands" ]] && debug="-x"
bash $debug script
Quoting this doesn't work, since in the default case, "$debug"
would expand to one empty argument while $debug
would expand into zero arguments. In this case, you can use an array with zero or one elements as outlined above, or you can use an unquoted expansion with an alternate value:
debug=""
[[ $1 == "--trace-commands" ]] && debug="yes"
bash ${debug:+"-x"} script
This is better than an unquoted value because the alternative value can be properly quoted, e.g. wget ${output:+ -o "$output"}
.
As always, this warning can be [[ignore]]d on a case-by-case basis.
this is especially relevant when BASH many not be available for the array work around. For example, use in eval or in command options where script has total control of the variables...
FLAGS="-av -e 'ssh -x' --delete --delete-excluded"
...
# shellcheck disable=SC2086
eval rsync $FLAGS ~/dir remote_host:dir
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
PROXY_ENV appears unused. Verify it or export it. Open
PROXY_ENV="http_proxy=${SQUID} https_proxy=${SQUID}"
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foo appears unused. Verify it or export it.
Problematic code:
foo=42
echo "$FOO"
Correct code:
foo=42
echo "$foo"
Rationale:
Variables not used for anything are often associated with bugs, so ShellCheck warns about them.
Also note that something like local let foo=42
does not make a let
statement local -- it instead declares an additional local variable named let
.
Exceptions
ShellCheck may not always realize that the variable is in use (especially with indirection), and may not realize you don't care (with throwaway variables or unimplemented features).
For throwaway variables, consider using _
as a dummy:
read _ last _ zip _ _ <<< "$str"
echo "$last, $zip"
or use a directive to disable the warning:
# shellcheck disable=SC2034
read first last email zip lat lng <<< "$str"
echo "$last, $zip"
For indirection, there's not much you can do without rewriting to use arrays or similar:
bar=42 # will always appear unused
foo=bar
echo "${!foo}"
This is expected behavior, and not a bug. There is no good way to statically analyze indirection in shell scripts, just like static C analyzers have a hard time preventing segfaults.
As always, there are ways to [[ignore]] this and other messages if they frequently get in your way.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Double quote to prevent globbing and word splitting. Open
exec ${RAILS} runner $(readlink -f $(dirname $0))/3scale $*
- Read upRead up
- Exclude checks
Double quote to prevent globbing and word splitting.
Problematic code:
echo $1
for i in $*; do :; done # this done and the next one also applies to expanding arrays.
for i in $@; do :; done
Correct code:
echo "$1"
for i in "$@"; do :; done # or, 'for i; do'
Rationale
The first code looks like "print the first argument". It's actually "Split the first argument by IFS (spaces, tabs and line feeds). Expand each of them as if it was a glob. Join all the resulting strings and filenames with spaces. Print the result."
The second one looks like "iterate through all arguments". It's actually "join all the arguments by the first character of IFS (space), split them by IFS and expand each of them as globs, and iterate on the resulting list". The third one skips the joining part.
Quoting variables prevents word splitting and glob expansion, and prevents the script from breaking when input contains spaces, line feeds, glob characters and such.
Strictly speaking, only expansions themselves need to be quoted, but for stylistic reasons, entire arguments with multiple variable and literal parts are often quoted as one:
$HOME/$dir/dist/bin/$file # Unquoted (bad)
"$HOME"/"$dir"/dist/bin/"$file" # Minimal quoting (good)
"$HOME/$dir/dist/bin/$file" # Canonical quoting (good)
When quoting composite arguments, make sure to exclude globs and brace expansions, which lose their special meaning in double quotes: "$HOME/$dir/src/*.c"
will not expand, but "$HOME/$dir/src"/*.c
will.
Note that $( )
starts a new context, and variables in it have to be quoted independently:
echo "This $variable is quoted $(but this $variable is not)"
echo "This $variable is quoted $(and now this "$variable" is too)"
Exceptions
Sometimes you want to split on spaces, like when building a command line:
options="-j 5 -B"
make $options file
Just quoting this doesn't work. Instead, you should have used an array (bash, ksh, zsh):
options=(-j 5 -B) # ksh: set -A options -- -j 5 -B
make "${options[@]}" file
or a function (POSIX):
make_with_flags() { make -j 5 -B "$@"; }
make_with_flags file
To split on spaces but not perform glob expansion, Posix has a set -f
to disable globbing. You can disable word splitting by setting IFS=''
.
Similarly, you might want an optional argument:
debug=""
[[ $1 == "--trace-commands" ]] && debug="-x"
bash $debug script
Quoting this doesn't work, since in the default case, "$debug"
would expand to one empty argument while $debug
would expand into zero arguments. In this case, you can use an array with zero or one elements as outlined above, or you can use an unquoted expansion with an alternate value:
debug=""
[[ $1 == "--trace-commands" ]] && debug="yes"
bash ${debug:+"-x"} script
This is better than an unquoted value because the alternative value can be properly quoted, e.g. wget ${output:+ -o "$output"}
.
As always, this warning can be [[ignore]]d on a case-by-case basis.
this is especially relevant when BASH many not be available for the array work around. For example, use in eval or in command options where script has total control of the variables...
FLAGS="-av -e 'ssh -x' --delete --delete-excluded"
...
# shellcheck disable=SC2086
eval rsync $FLAGS ~/dir remote_host:dir
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Use "$@" (with quotes) to prevent whitespace problems. Open
exec ${RAILS} runner $(readlink -f $(dirname $0))/3scale $*
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Use "$@" (with quotes) to prevent whitespace problems.
Problematic code:
cp $* ~/dir
Correct code:
cp "$@" ~/dir
Rationale:
$*
, unquoted, is subject to word splitting and globbing.
Let's say you have three arguments: baz
, foo bar
and *
"$@"
will expand into exactly that: baz
, foo bar
and *
$*
will expand into multiple other arguments: baz
, foo
, bar
, file.txt
and otherfile.jpg
Since the latter is rarely expected or desired, ShellCheck warns about it.
Exceptions
None.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Quote this to prevent word splitting. Open
exec ${RAILS} runner $(readlink -f $(dirname $0))/3scale $*
- Read upRead up
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Quote this to prevent word splitting
Problematic code:
ls -l $(getfilename)
Correct code:
# getfilename outputs 1 file
ls -l "$(getfilename)"
# getfilename outputs multiple files, linefeed separated
getfilename | while IFS='' read -r line
do
ls -l "$line"
done
Rationale:
When command expansions are unquoted, word splitting and globbing will occur. This often manifests itself by breaking when filenames contain spaces.
Trying to fix it by adding quotes or escapes to the data will not work. Instead, quote the command substitution itself.
If the command substitution outputs multiple pieces of data, use a loop instead.
Exceptions
In rare cases you actually want word splitting, such as in
gcc $(pkg-config --libs openssl) client.c
This is because pkg-config
outputs -lssl -lcrypto
, which you want to break up by spaces into -lssl
and -lcrypto
. An alternative is to put the variables to an array and expand it:
args=( $(pkg-config --libs openssl) )
gcc "${args[@]}" client.c
The power of using an array becomes evident when you want to combine, for example, the command result with user-provided arguments:
compile () {
args=( $(pkg-config --libs openssl) "${@}" )
gcc "${args[@]}" client.c
}
compile -DDEBUG
+ gcc -lssl -lcrypto -DDEBUG client.c
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
!important should not be used Open
padding: line-height-times(1/3) line-height-times(1/2) !important;
- Exclude checks
1/3
should be written with a single space on each side of the operator: 1 / 3
Open
padding: line-height-times(1/3) line-height-times(1/2) !important;
- Exclude checks
3/2
should be written with a single space on each side of the operator: 3 / 2
Open
height: line-height-times(3/2);
- Exclude checks
1/4
should be written with a single space on each side of the operator: 1 / 4
Open
padding: line-height-times(1/4) line-height-times(1/3) !important;
- Exclude checks
Properties should be ordered background-color, bottom, color, padding, position, text-align, width, z-index Open
color: $call-to-action-color;
- Exclude checks
Opening curly brace {
should be preceded by one space Open
#colorbox, #cboxOverlay, #cboxWrapper{
- Exclude checks
Colon after property should be followed by one space Open
position:absolute;
- Exclude checks
Properties should be ordered left, min-width, overflow, position, top, -webkit-transform, z-index Open
position:absolute;
- Exclude checks
Shorthand form for property margin
should be written more concisely as 0
instead of 0 0 0 0
Open
margin: 0 0 0 0;
- Exclude checks
Each selector in a comma sequence should be on its own single line Open
table .important-button, .important-button, .formtastic .important-button {
- Exclude checks
!important should not be used Open
padding: line-height-times(1/4) line-height-times(1/3) !important;
- Exclude checks
1/4
should be written with a single space on each side of the operator: 1 / 4
Open
padding: line-height-times(1/8) line-height-times(1/4);
- Exclude checks
Avoid using id selectors Open
#colorbox {
- Exclude checks
Expected item on line 42 to appear before line 41. Rule sets should be ordered as follows: @extends
, @includes
without @content
, properties, @includes
with @content
, nested rule sets Open
@include internal-potato-button($important-button-color, $important-button-bg-color, $important-button-border-color);
- Exclude checks