Showing 270 of 270 total issues
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 $(..) instead of legacy ..
. Open
[ ! -L "`pwd`/${websiteDir}/pub" ] && ln -s `pwd`/pub "`pwd`/${websiteDir}/pub"
- 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.
$(STATEMENT)
command substitution has none of these problems, and is therefore strongly encouraged.
Exceptions
None.
See also
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Declare and assign separately to avoid masking return values. Open
local yellow=`tput setaf 3`
- Read upRead up
- Exclude checks
Declare and assign separately to avoid masking return values.
Problematic code:
export foo="$(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 $(..) instead of legacy ..
. Open
MAGENTO_MAJOR_VERSION=`echo "${REAL_MAGENTO_VERSION}" | sed 's/.*2\.\([0-9]*\)\.\([0-9]*\).*/\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
if [ $MAGENTO_MAJOR_VERSION -ge 4 ] && [ $MAGENTO_MINOR_VERSION -ge 1 ]
- 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 $FLAGS ~/dir remote_host:dir
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Declare and assign separately to avoid masking return values. Open
local esport=$(getESConfigPort "$searchEngine")
- Read upRead up
- Exclude checks
Declare and assign separately to avoid masking return values.
Problematic code:
export foo="$(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
askValue "Git branch" ${MAGENTO_VERSION}
- 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 $FLAGS ~/dir remote_host:dir
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Declare and assign separately to avoid masking return values. Open
local isBranchExists=$(${BIN_GIT} ls-remote ${repoName} | grep -F ${versionName})
- Read upRead up
- Exclude checks
Declare and assign separately to avoid masking return values.
Problematic code:
export foo="$(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 2.2.4-p10")
- 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.
Arrays implicitly concatenate in [[ ]]. Use a loop (or explicit * instead of @). Open
if [[ "${STEPS[@]}" ]]
- Read upRead up
- Exclude checks
Arrays implicitly concatenate in [[ ]]
. Use a loop (or explicit * instead of @).
Problematic code:
ext=png
allowedExt=(jpg bmp png)
[[ "$ext" = "${allowedExt[@]}" ]] && echo "Extension is valid"
Correct code:
ext=png
allowedExt=(jpg bmp png)
for value in "${allowedExt[@]}"
do
[[ "$ext" = "$value" ]] && echo "Extension is valid"
done
Rationale:
Array expansions in [[ .. ]]
will implicitly concatenate into a single string, much like in assignments. The problematic code is equivalent to [ "$ext" = "jpg bmp png" ]
.
Instead, use a for
loop to iterate over values, and apply your condition to each.
Alternatively, if you do want to concatenate all the values in the array into a single string for your test, use "$*"
or "${array[*]}"
to make this explicit.
Exceptions:
None.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Declare and assign separately to avoid masking return values. Open
local default=`tput sgr0`
- Read upRead up
- Exclude checks
Declare and assign separately to avoid masking return values.
Problematic code:
export foo="$(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
if [ ! -z $2 ]
- 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 $(..) instead of legacy ..
. Open
REAL_MAGENTO_VERSION=`${BIN_PHP} bin/magento --version`
- 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
if [ $MAGENTO_MAJOR_VERSION -ge 4 ] && [ $MAGENTO_MINOR_VERSION -ge 1 ]
- 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 $(..) instead of legacy ..
. Open
B2B_VERSION_MAJOR=$(( `echo "${MAGENTO_MAJOR_VERSION}"` -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.
$(STATEMENT)
command substitution has none of these problems, and is therefore strongly encouraged.
Exceptions
None.
See also
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Double quote to prevent globbing and word splitting. Open
CMD="${CMD} --search-engine=$searchEngine --elasticsearch-host=$(getESConfigHost $searchEngine) --elasticsearch-port=$(getESConfigPort $searchEngine) --elasticsearch-index-prefix=${DB_NAME}"
- 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.
See if you can use ${variable//search/replace} instead. Open
MAGENTO_PATCH_VERSION=`echo "${REAL_MAGENTO_VERSION}" | sed 's/.*2\.\([0-9]*\)\.\([0-9]*\).\([a-z0-9]*\)/\3/'`
- 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/^.*\(.\)$/\1/"
This is a bit simple for the example and there are alternative ways of doing this in the shell, but this SC2001 flags on several of my crazy complex sed commands which are beyond the scope of this example. Utilizing some of the more complex capabilities of sed is required occasionally and it is safe to ignore SC2001.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Declare and assign separately to avoid masking return values. Open
local eshost=$(getESConfigHost "$searchEngine")
- Read upRead up
- Exclude checks
Declare and assign separately to avoid masking return values.
Problematic code:
export foo="$(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=$(cmd)
, where declaration and assignment must be in the same command.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Quote this to prevent word splitting. Open
searchEngine="$(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 "${args[@]}" client.c
}
compile -DDEBUG
+ gcc -lssl -lcrypto -DDEBUG client.c
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
Declare and assign separately to avoid masking return values. Open
local worktreeCEPath="$(getWorktreePath CE)"
- 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.