Showing 270 of 270 total issues
Double quote to prevent globbing and word splitting. Open
local isBranchExists=$(${BIN_GIT} ls-remote ${repoName} | grep -F ${versionName})
- 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.
Quote this to prevent word splitting. Open
$BIN_PHP $BIN_MAGE --quiet config:set 'catalog/search/engine' $(getRecommendedSearchEngineForVersion)
- Read upRead up
- Exclude checks
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 "${args[@]}" client.c
}
compile -DDEBUG
+ gcc -lssl -lcrypto -DDEBUG client.c
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
green appears unused. Verify it or export it. Open
local green=`tput setaf 2`
- Read upRead up
- Exclude checks
foo appears unused. Verify it or export it.
Problematic code:
foo=42
echo "$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.
Declare and assign separately to avoid masking return values. Open
local deployConfigurator=$(cat << EOF
- Read upRead up
- Exclude checks
Declare and assign separately to avoid masking return values.
Problematic code:
export foo="$(mycmd)"
Correct code:
foo=$(mycmd)
export foo
Rationale:
In the original code, the return value of mycmd
is ignored, and export
will instead always return true. This may prevent conditionals, set -e
and traps from working correctly.
When first marked for export and assigned separately, the return value of the assignment will be that of mycmd
. This avoids the problem.
Exceptions:
If you intend to ignore the return value of an assignment, you can either ignore this warning or use
foo=$(mycmd) || true
export foo
Shellcheck does not warn about export foo=bar
because bar
is a literal and not a command substitution with an independent return value. It also does not warn about local -r foo=$(cmd)
, where declaration and assignment must be in the same command.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
See if you can use ${variable//search/replace} instead. Open
MAGENTO_MAJOR_VERSION=`echo "${REAL_MAGENTO_VERSION}" | sed 's/.*2\.\([0-9]*\)\.\([0-9]*\).*/\1/'`
- Read upRead up
- Exclude checks
SC2001: See if you can use ${variable//search/replace} instead.
Problematic code:
string="stirng" ; echo "$string" | sed -e "s/ir/ri/"
Correct code:
string="stirng" ; echo "${string//ir/ri}"
Rationale:
Let's assume somewhere earlier in your code you have put data into a variable (Ex: $string). Now you want to do a search and replace inside the contents of $string and echo the contents out. You could pass this to sed as done in the example above, but for simple substitutions utilizing the shell for the same feature is a lot simpler and should be utilized whenever possible.
Exceptions
Occasionally a more complex sed substitution is required. For example, getting the last character of a string.
string="stirng" ; echo "$string" | sed -e "s/^.*\(.\)$/\1/"
This is a bit simple for the example and there are alternative ways of doing this in the shell, but this SC2001 flags on several of my crazy complex sed commands which are beyond the scope of this example. Utilizing some of the more complex capabilities of sed is required occasionally and it is safe to ignore SC2001.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
See if you can use ${variable//search/replace} instead. Open
MAGENTO_MINOR_VERSION=`echo "${REAL_MAGENTO_VERSION}" | sed 's/.*2\.\([0-9]*\)\.\([0-9]*\).*/\2/'`
- Read upRead up
- Exclude checks
SC2001: See if you can use ${variable//search/replace} instead.
Problematic code:
string="stirng" ; echo "$string" | sed -e "s/ir/ri/"
Correct code:
string="stirng" ; echo "${string//ir/ri}"
Rationale:
Let's assume somewhere earlier in your code you have put data into a variable (Ex: $string). Now you want to do a search and replace inside the contents of $string and echo the contents out. You could pass this to sed as done in the example above, but for simple substitutions utilizing the shell for the same feature is a lot simpler and should be utilized whenever possible.
Exceptions
Occasionally a more complex sed substitution is required. For example, getting the last character of a string.
string="stirng" ; echo "$string" | sed -e "s/^.*\(.\)$/\1/"
This is a bit simple for the example and there are alternative ways of doing this in the shell, but this SC2001 flags on several of my crazy complex sed commands which are beyond the scope of this example. Utilizing some of the more complex capabilities of sed is required occasionally and it is safe to ignore SC2001.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Double quote to prevent globbing and word splitting. Open
if [ -z ${!configName} ]
- 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.
Double quote to prevent globbing and word splitting. Open
$BIN_PHP $BIN_MAGE module:status $moduleName | grep -q 'Module is enabled' && $BIN_PHP $BIN_MAGE module:disable $moduleName && echo "$moduleName is being disabled"
- 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 $FLAGS ~/dir remote_host:dir
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Use 'cd ... || exit' or 'cd ... || return' in case cd fails. Open
local homeDirectory="$(cd ~; pwd)"
- Read upRead up
- Exclude checks
Use cd ... || exit in case cd fails.
Problematic code:
cd generated_files
rm -r *.c
func(){
cd foo
do_something
}
Correct code:
cd generated_files || exit
rm -r *.c
# For functions, you may want to use return:
func(){
cd foo || return
do_something
}
Rationale:
cd
can fail for a variety of reasons: misspelled paths, missing directories, missing permissions, broken symlinks and more.
If/when it does, the script will keep going and do all its operations in the wrong directory. This can be messy, especially if the operations involve creating or deleting a lot of files.
To avoid this, make sure you handle the cases when cd
fails. Ways to do this include
-
cd foo || exit
as suggested to just abort immediately -
if cd foo; then echo "Ok"; else echo "Fail"; fi
for custom handling -
<(cd foo && cmd)
as an alternative to<(cd foo || exit; cmd)
in<(..)
,$(..)
or( )
Exceptions:
ShellCheck does not give this warning when cd
is on the left of a ||
or &&
, or the condition of a if
, while
or until
loop. Having a set -e
command anywhere in the script will disable this message, even though it won't necessarily prevent the issue.
If you are accounting for cd
failures in a way shellcheck doesn't realize, you can disable this message with a [[directive]].
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Declare and assign separately to avoid masking return values. Open
local esRequired=$(php -r "echo (version_compare('$mageVersion', '$defaultVersion') >= 0) ? 'REQUIRED' : 'NO';")
- Read upRead up
- Exclude checks
Declare and assign separately to avoid masking return values.
Problematic code:
export foo="$(mycmd)"
Correct code:
foo=$(mycmd)
export foo
Rationale:
In the original code, the return value of mycmd
is ignored, and export
will instead always return true. This may prevent conditionals, set -e
and traps from working correctly.
When first marked for export and assigned separately, the return value of the assignment will be that of mycmd
. This avoids the problem.
Exceptions:
If you intend to ignore the return value of an assignment, you can either ignore this warning or use
foo=$(mycmd) || true
export foo
Shellcheck does not warn about export foo=bar
because bar
is a literal and not a command substitution with an independent return value. It also does not warn about local -r foo=$(cmd)
, where declaration and assignment must be in the same command.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Use $(..) instead of legacy ..
. Open
local green=`tput setaf 2`
- Read upRead up
- Exclude checks
Use $(STATEMENT) instead of legacy `STATEMENT`
Problematic code
echo "Current time: `date`"
Correct code
echo "Current time: $(date)"
Rationale
Backtick command substitution `STATEMENT`
is legacy syntax with several issues.
- It has a series of undefined behaviors related to quoting in POSIX.
- It imposes a custom escaping mode with surprising results.
- It's exceptionally hard to nest.
$(STATEMENT)
command substitution has none of these problems, and is therefore strongly encouraged.
Exceptions
None.
See also
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Use $(..) instead of legacy ..
. Open
B2B_VERSION_MAJOR=$(( `echo "${MAGENTO_MAJOR_VERSION}"` -1 ))
- Read upRead up
- Exclude checks
Use $(STATEMENT) instead of legacy `STATEMENT`
Problematic code
echo "Current time: `date`"
Correct code
echo "Current time: $(date)"
Rationale
Backtick command substitution `STATEMENT`
is legacy syntax with several issues.
- It has a series of undefined behaviors related to quoting in POSIX.
- It imposes a custom escaping mode with surprising results.
- It's exceptionally hard to nest.
$(STATEMENT)
command substitution has none of these problems, and is therefore strongly encouraged.
Exceptions
None.
See also
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Quote this to prevent word splitting. Open
searchEngine="$(parseElasticSearchVersion $(getESConfigHost) $(getESConfigPort))"
- Read upRead up
- Exclude checks
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 "${args[@]}" client.c
}
compile -DDEBUG
+ gcc -lssl -lcrypto -DDEBUG client.c
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Use 'cd ... || exit' or 'cd ... || return' in case cd fails. Open
cd "$currentDir"
- Read upRead up
- Exclude checks
Use cd ... || exit in case cd fails.
Problematic code:
cd generated_files
rm -r *.c
func(){
cd foo
do_something
}
Correct code:
cd generated_files || exit
rm -r *.c
# For functions, you may want to use return:
func(){
cd foo || return
do_something
}
Rationale:
cd
can fail for a variety of reasons: misspelled paths, missing directories, missing permissions, broken symlinks and more.
If/when it does, the script will keep going and do all its operations in the wrong directory. This can be messy, especially if the operations involve creating or deleting a lot of files.
To avoid this, make sure you handle the cases when cd
fails. Ways to do this include
-
cd foo || exit
as suggested to just abort immediately -
if cd foo; then echo "Ok"; else echo "Fail"; fi
for custom handling -
<(cd foo && cmd)
as an alternative to<(cd foo || exit; cmd)
in<(..)
,$(..)
or( )
Exceptions:
ShellCheck does not give this warning when cd
is on the left of a ||
or &&
, or the condition of a if
, while
or until
loop. Having a set -e
command anywhere in the script will disable this message, even though it won't necessarily prevent the issue.
If you are accounting for cd
failures in a way shellcheck doesn't realize, you can disable this message with a [[directive]].
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Declare and assign separately to avoid masking return values. Open
local homeDirectory="$(cd ~; pwd)"
- Read upRead up
- Exclude checks
Declare and assign separately to avoid masking return values.
Problematic code:
export foo="$(mycmd)"
Correct code:
foo=$(mycmd)
export foo
Rationale:
In the original code, the return value of mycmd
is ignored, and export
will instead always return true. This may prevent conditionals, set -e
and traps from working correctly.
When first marked for export and assigned separately, the return value of the assignment will be that of mycmd
. This avoids the problem.
Exceptions:
If you intend to ignore the return value of an assignment, you can either ignore this warning or use
foo=$(mycmd) || true
export foo
Shellcheck does not warn about export foo=bar
because bar
is a literal and not a command substitution with an independent return value. It also does not warn about local -r foo=$(cmd)
, where declaration and assignment must be in the same command.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Declare and assign separately to avoid masking return values. Open
local result=$(parseMagentoVersion "Magento CLI 2.3.4")
- Read upRead up
- Exclude checks
Declare and assign separately to avoid masking return values.
Problematic code:
export foo="$(mycmd)"
Correct code:
foo=$(mycmd)
export foo
Rationale:
In the original code, the return value of mycmd
is ignored, and export
will instead always return true. This may prevent conditionals, set -e
and traps from working correctly.
When first marked for export and assigned separately, the return value of the assignment will be that of mycmd
. This avoids the problem.
Exceptions:
If you intend to ignore the return value of an assignment, you can either ignore this warning or use
foo=$(mycmd) || true
export foo
Shellcheck does not warn about export foo=bar
because bar
is a literal and not a command substitution with an independent return value. It also does not warn about local -r foo=$(cmd)
, where declaration and assignment must be in the same command.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Double quote to prevent globbing and word splitting. Open
$BIN_PHP $BIN_MAGE module:status | grep -E 'Magento_Elasticsearch*|Magento_AdvancedSearch|Magento_InventoryElasticsearch' | grep -v List | grep -v None | grep -v -e '^$' | xargs $BIN_PHP $BIN_MAGE module:enable
- 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 $(..) instead of legacy ..
. Open
local red=`tput setaf 1`
- Read upRead up
- Exclude checks
Use $(STATEMENT) instead of legacy `STATEMENT`
Problematic code
echo "Current time: `date`"
Correct code
echo "Current time: $(date)"
Rationale
Backtick command substitution `STATEMENT`
is legacy syntax with several issues.
- It has a series of undefined behaviors related to quoting in POSIX.
- It imposes a custom escaping mode with surprising results.
- It's exceptionally hard to nest.
$(STATEMENT)
command substitution has none of these problems, and is therefore strongly encouraged.
Exceptions
None.
See also
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Double quote to prevent globbing and word splitting. Open
$BIN_PHP $BIN_MAGE module:status | grep Magento_LiveSearch | grep -v List | grep -v None | grep -v -e '^$' | xargs $BIN_PHP $BIN_MAGE module:enable
- 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 $FLAGS ~/dir remote_host:dir
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
The surrounding quotes actually unquote this. Remove or escape them. Open
CMD="[ ! -d "$B2B_VERSION" ] && ${BIN_GIT} clone --branch ${B2B_VERSION} --single-branch ${GIT_B2B_REPO} ${GIT_B2B_PATH}"
- Read upRead up
- Exclude checks
The surrounding quotes actually unquote this. Remove or escape them.
Problematic code:
echo "You enter "$HOSTNAME". You can smell the wumpus." >> /etc/issue
Correct code:
echo "You enter $HOSTNAME. You can smell the wumpus." >> /etc/issue
Rationale:
Always quoting variables and command expansions is good practice, but blindly putting quotes left and right of them is not.
In this case, ShellCheck has noticed that the quotes around the expansion are unquoting it, because the left quote is terminating an existing double quoted string, while the right quote starts a new one:
echo "You enter "$HOSTNAME". You can smell the wumpus."
|----------| |---------------------------|
Quoted No quotes Quoted
If the quotes were supposed to be literal, they should be escaped. If the quotes were supposed to quote an expansion (as in the example), they should be removed because this is already a double quoted string.
Exceptions
None.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.