In POSIX sh, ulimit -t is undefined. Open
ulimit -t unlimited || exit 1
- Read upRead up
- Exclude checks
In POSIX sh, something is undefined.
You have declared that your script works with /bin/sh
, but you are using features that have undefined behavior according to the POSIX specification.
It may currently work for you, but it can or will fail on other OS, the same OS with different configurations, from different contexts (like initramfs/chroot), or in different versions of the same OS, including future updates to your current system.
Either declare that your script requires a specific shell like #!/bin/bash
or #!/bin/dash
, or rewrite the script in a portable way.
For help with rewrites, the Ubuntu wiki has a list of portability issues that broke people's #!/bin/sh
scripts when Ubuntu switched from Bash to Dash. See also Bashism on wooledge's wiki. ShellCheck may not warn about all these issues.
$'c-style-escapes'
bash, ksh:
a=$' \t\n'
POSIX:
a="$(printf '%b_' ' \t\n')"; a="${a%_}" # protect trailing \n
Want some good news? See http://austingroupbugs.net/view.php?id=249#c590.
$"msgid"
Bash:
echo $"foo $(bar) baz"
POSIX:
. gettext.sh # GNU Gettext sh library
# ...
barout=$(bar)
eval_gettext 'foo $barout baz' # See GNU Gettext doc for more info.
Or you can change them to normal double quotes so you go without gettext
.
Arithmetic for
loops
Bash:
for ((init; test; next)); do foo; done
POSIX:
: $((init))
while [ $((test)) -ne 0 ]; do foo; : $((next)); done
Arithmetic exponentiation
Bash:
printf "%s\n" "$(( 2**63 ))"
POSIX:
The POSIX standard does not allow for exponents. However, you can replicate them completely built-in using a POSIX compatible function. As an example, the pow
function from here.
pow () {
set "$1" "$2" 1
while [ "$2" -gt 0 ]; do
set "$1" $(($2-1)) $(($1*$3))
done
# %d = signed decimal, %u = unsigned decimal
# Either should overflow to 0
printf "%d\n" "$3"
}
To compare:
$ echo "$(( 2**62 ))"
4611686018427387904
$ pow 2 62
4611686018427387904
Alternatively, if you don't mind using an external program, you can use bc
. Be aware though: bash
and other programs may abide by a certain maximum integer that bc
does not (for bash
that's: 64-bit signed long int, failing back to 32-bit signed long int).
Example:
# Note the overflow that gives a negative number
$ echo "$(( 2**63 ))"
-9223372036854775808
# No such problem
$ echo 2^63 | bc
9223372036854775808
# 'bc' just keeps on going
$ echo 2^1280 | bc
20815864389328798163850480654728171077230524494533409610638224700807\
21611934672059602447888346464836968484322790856201558276713249664692\
98162798132113546415258482590187784406915463666993231671009459188410\
95379622423387354295096957733925002768876520583464697770622321657076\
83317005651120933244966378183760369413644440628104205339687097746591\
6057756101739472373801429441421111406337458176
standalone ((..))
Bash:
((a=c+d))
((d)) && echo d is true.
POSIX:
: $((a=c+d)) # discard the output of the arith expn with `:` command
[ $((d)) -ne 0 ] && echo d is true. # manually check non-zero => true
select
loops
It takes extra care over terminal columns to make select loop look like bash's, which generates a list with multiple items on one line, or like ls
.
It is, however, still possible to make a naive translation for select foo in bar baz; do eat; done
:
while
_i=0 _foo= foo=
for _name in bar baz; do echo "$((_i+=1))) $_name"; done
printf '$# '; read _foo
do
case _foo in 1) foo=bar;; 2) foo=baz;; *) continue;; esac
eat
done
Here-strings
Bash, ksh:
grep aaa <<< "$g"
POSIX:
# not exactly the same -- <<< adds a trailing \n if $g doesn't end with \n
printf '%s' "$g" | grep aaa
echo flags
See https://unix.stackexchange.com/tags/echo/info.
${var/pat/replacement}
Bash:
echo "${TERM/%-256*}"
POSIX:
echo "$TERM" | sed -e 's/-256.*$//g'
# Special case for this since we are matching the end:
echo "${TERM%-256*}"
printf %q
Bash:
printf '%q ' "$@"
POSIX:
# TODO: Interpret it back to printf escapes for hard-to-copy chars like \t?
# See also: http://git.savannah.gnu.org/cgit/libtool.git/tree/gl/build-aux/funclib.sh?id=c60e054#n1029
reuse_quote()(
for i; do
__i_quote=$(printf '%s\n' "$i" | sed -e "s/'/'\\\\''/g"; echo x)
printf "'%s'" "${__i_quote%x}"
done
)
reuse_quote "$@"
Exception
Depends on what your expected POSIX shell providers would use.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
In POSIX sh, 'shopt' is undefined. Open
if shopt -s failglob 2>/dev/null; then
- Read upRead up
- Exclude checks
In POSIX sh, something is undefined.
You have declared that your script works with /bin/sh
, but you are using features that have undefined behavior according to the POSIX specification.
It may currently work for you, but it can or will fail on other OS, the same OS with different configurations, from different contexts (like initramfs/chroot), or in different versions of the same OS, including future updates to your current system.
Either declare that your script requires a specific shell like #!/bin/bash
or #!/bin/dash
, or rewrite the script in a portable way.
For help with rewrites, the Ubuntu wiki has a list of portability issues that broke people's #!/bin/sh
scripts when Ubuntu switched from Bash to Dash. See also Bashism on wooledge's wiki. ShellCheck may not warn about all these issues.
$'c-style-escapes'
bash, ksh:
a=$' \t\n'
POSIX:
a="$(printf '%b_' ' \t\n')"; a="${a%_}" # protect trailing \n
Want some good news? See http://austingroupbugs.net/view.php?id=249#c590.
$"msgid"
Bash:
echo $"foo $(bar) baz"
POSIX:
. gettext.sh # GNU Gettext sh library
# ...
barout=$(bar)
eval_gettext 'foo $barout baz' # See GNU Gettext doc for more info.
Or you can change them to normal double quotes so you go without gettext
.
Arithmetic for
loops
Bash:
for ((init; test; next)); do foo; done
POSIX:
: $((init))
while [ $((test)) -ne 0 ]; do foo; : $((next)); done
Arithmetic exponentiation
Bash:
printf "%s\n" "$(( 2**63 ))"
POSIX:
The POSIX standard does not allow for exponents. However, you can replicate them completely built-in using a POSIX compatible function. As an example, the pow
function from here.
pow () {
set "$1" "$2" 1
while [ "$2" -gt 0 ]; do
set "$1" $(($2-1)) $(($1*$3))
done
# %d = signed decimal, %u = unsigned decimal
# Either should overflow to 0
printf "%d\n" "$3"
}
To compare:
$ echo "$(( 2**62 ))"
4611686018427387904
$ pow 2 62
4611686018427387904
Alternatively, if you don't mind using an external program, you can use bc
. Be aware though: bash
and other programs may abide by a certain maximum integer that bc
does not (for bash
that's: 64-bit signed long int, failing back to 32-bit signed long int).
Example:
# Note the overflow that gives a negative number
$ echo "$(( 2**63 ))"
-9223372036854775808
# No such problem
$ echo 2^63 | bc
9223372036854775808
# 'bc' just keeps on going
$ echo 2^1280 | bc
20815864389328798163850480654728171077230524494533409610638224700807\
21611934672059602447888346464836968484322790856201558276713249664692\
98162798132113546415258482590187784406915463666993231671009459188410\
95379622423387354295096957733925002768876520583464697770622321657076\
83317005651120933244966378183760369413644440628104205339687097746591\
6057756101739472373801429441421111406337458176
standalone ((..))
Bash:
((a=c+d))
((d)) && echo d is true.
POSIX:
: $((a=c+d)) # discard the output of the arith expn with `:` command
[ $((d)) -ne 0 ] && echo d is true. # manually check non-zero => true
select
loops
It takes extra care over terminal columns to make select loop look like bash's, which generates a list with multiple items on one line, or like ls
.
It is, however, still possible to make a naive translation for select foo in bar baz; do eat; done
:
while
_i=0 _foo= foo=
for _name in bar baz; do echo "$((_i+=1))) $_name"; done
printf '$# '; read _foo
do
case _foo in 1) foo=bar;; 2) foo=baz;; *) continue;; esac
eat
done
Here-strings
Bash, ksh:
grep aaa <<< "$g"
POSIX:
# not exactly the same -- <<< adds a trailing \n if $g doesn't end with \n
printf '%s' "$g" | grep aaa
echo flags
See https://unix.stackexchange.com/tags/echo/info.
${var/pat/replacement}
Bash:
echo "${TERM/%-256*}"
POSIX:
echo "$TERM" | sed -e 's/-256.*$//g'
# Special case for this since we are matching the end:
echo "${TERM%-256*}"
printf %q
Bash:
printf '%q ' "$@"
POSIX:
# TODO: Interpret it back to printf escapes for hard-to-copy chars like \t?
# See also: http://git.savannah.gnu.org/cgit/libtool.git/tree/gl/build-aux/funclib.sh?id=c60e054#n1029
reuse_quote()(
for i; do
__i_quote=$(printf '%s\n' "$i" | sed -e "s/'/'\\\\''/g"; echo x)
printf "'%s'" "${__i_quote%x}"
done
)
reuse_quote "$@"
Exception
Depends on what your expected POSIX shell providers would use.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
In POSIX sh, 'readarray' is undefined. Open
if readarray </dev/null 2>/dev/null; then
- Read upRead up
- Exclude checks
In POSIX sh, something is undefined.
You have declared that your script works with /bin/sh
, but you are using features that have undefined behavior according to the POSIX specification.
It may currently work for you, but it can or will fail on other OS, the same OS with different configurations, from different contexts (like initramfs/chroot), or in different versions of the same OS, including future updates to your current system.
Either declare that your script requires a specific shell like #!/bin/bash
or #!/bin/dash
, or rewrite the script in a portable way.
For help with rewrites, the Ubuntu wiki has a list of portability issues that broke people's #!/bin/sh
scripts when Ubuntu switched from Bash to Dash. See also Bashism on wooledge's wiki. ShellCheck may not warn about all these issues.
$'c-style-escapes'
bash, ksh:
a=$' \t\n'
POSIX:
a="$(printf '%b_' ' \t\n')"; a="${a%_}" # protect trailing \n
Want some good news? See http://austingroupbugs.net/view.php?id=249#c590.
$"msgid"
Bash:
echo $"foo $(bar) baz"
POSIX:
. gettext.sh # GNU Gettext sh library
# ...
barout=$(bar)
eval_gettext 'foo $barout baz' # See GNU Gettext doc for more info.
Or you can change them to normal double quotes so you go without gettext
.
Arithmetic for
loops
Bash:
for ((init; test; next)); do foo; done
POSIX:
: $((init))
while [ $((test)) -ne 0 ]; do foo; : $((next)); done
Arithmetic exponentiation
Bash:
printf "%s\n" "$(( 2**63 ))"
POSIX:
The POSIX standard does not allow for exponents. However, you can replicate them completely built-in using a POSIX compatible function. As an example, the pow
function from here.
pow () {
set "$1" "$2" 1
while [ "$2" -gt 0 ]; do
set "$1" $(($2-1)) $(($1*$3))
done
# %d = signed decimal, %u = unsigned decimal
# Either should overflow to 0
printf "%d\n" "$3"
}
To compare:
$ echo "$(( 2**62 ))"
4611686018427387904
$ pow 2 62
4611686018427387904
Alternatively, if you don't mind using an external program, you can use bc
. Be aware though: bash
and other programs may abide by a certain maximum integer that bc
does not (for bash
that's: 64-bit signed long int, failing back to 32-bit signed long int).
Example:
# Note the overflow that gives a negative number
$ echo "$(( 2**63 ))"
-9223372036854775808
# No such problem
$ echo 2^63 | bc
9223372036854775808
# 'bc' just keeps on going
$ echo 2^1280 | bc
20815864389328798163850480654728171077230524494533409610638224700807\
21611934672059602447888346464836968484322790856201558276713249664692\
98162798132113546415258482590187784406915463666993231671009459188410\
95379622423387354295096957733925002768876520583464697770622321657076\
83317005651120933244966378183760369413644440628104205339687097746591\
6057756101739472373801429441421111406337458176
standalone ((..))
Bash:
((a=c+d))
((d)) && echo d is true.
POSIX:
: $((a=c+d)) # discard the output of the arith expn with `:` command
[ $((d)) -ne 0 ] && echo d is true. # manually check non-zero => true
select
loops
It takes extra care over terminal columns to make select loop look like bash's, which generates a list with multiple items on one line, or like ls
.
It is, however, still possible to make a naive translation for select foo in bar baz; do eat; done
:
while
_i=0 _foo= foo=
for _name in bar baz; do echo "$((_i+=1))) $_name"; done
printf '$# '; read _foo
do
case _foo in 1) foo=bar;; 2) foo=baz;; *) continue;; esac
eat
done
Here-strings
Bash, ksh:
grep aaa <<< "$g"
POSIX:
# not exactly the same -- <<< adds a trailing \n if $g doesn't end with \n
printf '%s' "$g" | grep aaa
echo flags
See https://unix.stackexchange.com/tags/echo/info.
${var/pat/replacement}
Bash:
echo "${TERM/%-256*}"
POSIX:
echo "$TERM" | sed -e 's/-256.*$//g'
# Special case for this since we are matching the end:
echo "${TERM%-256*}"
printf %q
Bash:
printf '%q ' "$@"
POSIX:
# TODO: Interpret it back to printf escapes for hard-to-copy chars like \t?
# See also: http://git.savannah.gnu.org/cgit/libtool.git/tree/gl/build-aux/funclib.sh?id=c60e054#n1029
reuse_quote()(
for i; do
__i_quote=$(printf '%s\n' "$i" | sed -e "s/'/'\\\\''/g"; echo x)
printf "'%s'" "${__i_quote%x}"
done
)
reuse_quote "$@"
Exception
Depends on what your expected POSIX shell providers would use.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
In POSIX sh, 'typeset' is undefined. Open
set -- "$(var=data; typeset -p var 2>/dev/null ||:)" ||:
- Read upRead up
- Exclude checks
In POSIX sh, something is undefined.
You have declared that your script works with /bin/sh
, but you are using features that have undefined behavior according to the POSIX specification.
It may currently work for you, but it can or will fail on other OS, the same OS with different configurations, from different contexts (like initramfs/chroot), or in different versions of the same OS, including future updates to your current system.
Either declare that your script requires a specific shell like #!/bin/bash
or #!/bin/dash
, or rewrite the script in a portable way.
For help with rewrites, the Ubuntu wiki has a list of portability issues that broke people's #!/bin/sh
scripts when Ubuntu switched from Bash to Dash. See also Bashism on wooledge's wiki. ShellCheck may not warn about all these issues.
$'c-style-escapes'
bash, ksh:
a=$' \t\n'
POSIX:
a="$(printf '%b_' ' \t\n')"; a="${a%_}" # protect trailing \n
Want some good news? See http://austingroupbugs.net/view.php?id=249#c590.
$"msgid"
Bash:
echo $"foo $(bar) baz"
POSIX:
. gettext.sh # GNU Gettext sh library
# ...
barout=$(bar)
eval_gettext 'foo $barout baz' # See GNU Gettext doc for more info.
Or you can change them to normal double quotes so you go without gettext
.
Arithmetic for
loops
Bash:
for ((init; test; next)); do foo; done
POSIX:
: $((init))
while [ $((test)) -ne 0 ]; do foo; : $((next)); done
Arithmetic exponentiation
Bash:
printf "%s\n" "$(( 2**63 ))"
POSIX:
The POSIX standard does not allow for exponents. However, you can replicate them completely built-in using a POSIX compatible function. As an example, the pow
function from here.
pow () {
set "$1" "$2" 1
while [ "$2" -gt 0 ]; do
set "$1" $(($2-1)) $(($1*$3))
done
# %d = signed decimal, %u = unsigned decimal
# Either should overflow to 0
printf "%d\n" "$3"
}
To compare:
$ echo "$(( 2**62 ))"
4611686018427387904
$ pow 2 62
4611686018427387904
Alternatively, if you don't mind using an external program, you can use bc
. Be aware though: bash
and other programs may abide by a certain maximum integer that bc
does not (for bash
that's: 64-bit signed long int, failing back to 32-bit signed long int).
Example:
# Note the overflow that gives a negative number
$ echo "$(( 2**63 ))"
-9223372036854775808
# No such problem
$ echo 2^63 | bc
9223372036854775808
# 'bc' just keeps on going
$ echo 2^1280 | bc
20815864389328798163850480654728171077230524494533409610638224700807\
21611934672059602447888346464836968484322790856201558276713249664692\
98162798132113546415258482590187784406915463666993231671009459188410\
95379622423387354295096957733925002768876520583464697770622321657076\
83317005651120933244966378183760369413644440628104205339687097746591\
6057756101739472373801429441421111406337458176
standalone ((..))
Bash:
((a=c+d))
((d)) && echo d is true.
POSIX:
: $((a=c+d)) # discard the output of the arith expn with `:` command
[ $((d)) -ne 0 ] && echo d is true. # manually check non-zero => true
select
loops
It takes extra care over terminal columns to make select loop look like bash's, which generates a list with multiple items on one line, or like ls
.
It is, however, still possible to make a naive translation for select foo in bar baz; do eat; done
:
while
_i=0 _foo= foo=
for _name in bar baz; do echo "$((_i+=1))) $_name"; done
printf '$# '; read _foo
do
case _foo in 1) foo=bar;; 2) foo=baz;; *) continue;; esac
eat
done
Here-strings
Bash, ksh:
grep aaa <<< "$g"
POSIX:
# not exactly the same -- <<< adds a trailing \n if $g doesn't end with \n
printf '%s' "$g" | grep aaa
echo flags
See https://unix.stackexchange.com/tags/echo/info.
${var/pat/replacement}
Bash:
echo "${TERM/%-256*}"
POSIX:
echo "$TERM" | sed -e 's/-256.*$//g'
# Special case for this since we are matching the end:
echo "${TERM%-256*}"
printf %q
Bash:
printf '%q ' "$@"
POSIX:
# TODO: Interpret it back to printf escapes for hard-to-copy chars like \t?
# See also: http://git.savannah.gnu.org/cgit/libtool.git/tree/gl/build-aux/funclib.sh?id=c60e054#n1029
reuse_quote()(
for i; do
__i_quote=$(printf '%s\n' "$i" | sed -e "s/'/'\\\\''/g"; echo x)
printf "'%s'" "${__i_quote%x}"
done
)
reuse_quote "$@"
Exception
Depends on what your expected POSIX shell providers would use.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
In POSIX sh, trapping DEBUG is undefined. Open
trap '' DEBUG || exit 1
- Read upRead up
- Exclude checks
In POSIX sh, something is undefined.
You have declared that your script works with /bin/sh
, but you are using features that have undefined behavior according to the POSIX specification.
It may currently work for you, but it can or will fail on other OS, the same OS with different configurations, from different contexts (like initramfs/chroot), or in different versions of the same OS, including future updates to your current system.
Either declare that your script requires a specific shell like #!/bin/bash
or #!/bin/dash
, or rewrite the script in a portable way.
For help with rewrites, the Ubuntu wiki has a list of portability issues that broke people's #!/bin/sh
scripts when Ubuntu switched from Bash to Dash. See also Bashism on wooledge's wiki. ShellCheck may not warn about all these issues.
$'c-style-escapes'
bash, ksh:
a=$' \t\n'
POSIX:
a="$(printf '%b_' ' \t\n')"; a="${a%_}" # protect trailing \n
Want some good news? See http://austingroupbugs.net/view.php?id=249#c590.
$"msgid"
Bash:
echo $"foo $(bar) baz"
POSIX:
. gettext.sh # GNU Gettext sh library
# ...
barout=$(bar)
eval_gettext 'foo $barout baz' # See GNU Gettext doc for more info.
Or you can change them to normal double quotes so you go without gettext
.
Arithmetic for
loops
Bash:
for ((init; test; next)); do foo; done
POSIX:
: $((init))
while [ $((test)) -ne 0 ]; do foo; : $((next)); done
Arithmetic exponentiation
Bash:
printf "%s\n" "$(( 2**63 ))"
POSIX:
The POSIX standard does not allow for exponents. However, you can replicate them completely built-in using a POSIX compatible function. As an example, the pow
function from here.
pow () {
set "$1" "$2" 1
while [ "$2" -gt 0 ]; do
set "$1" $(($2-1)) $(($1*$3))
done
# %d = signed decimal, %u = unsigned decimal
# Either should overflow to 0
printf "%d\n" "$3"
}
To compare:
$ echo "$(( 2**62 ))"
4611686018427387904
$ pow 2 62
4611686018427387904
Alternatively, if you don't mind using an external program, you can use bc
. Be aware though: bash
and other programs may abide by a certain maximum integer that bc
does not (for bash
that's: 64-bit signed long int, failing back to 32-bit signed long int).
Example:
# Note the overflow that gives a negative number
$ echo "$(( 2**63 ))"
-9223372036854775808
# No such problem
$ echo 2^63 | bc
9223372036854775808
# 'bc' just keeps on going
$ echo 2^1280 | bc
20815864389328798163850480654728171077230524494533409610638224700807\
21611934672059602447888346464836968484322790856201558276713249664692\
98162798132113546415258482590187784406915463666993231671009459188410\
95379622423387354295096957733925002768876520583464697770622321657076\
83317005651120933244966378183760369413644440628104205339687097746591\
6057756101739472373801429441421111406337458176
standalone ((..))
Bash:
((a=c+d))
((d)) && echo d is true.
POSIX:
: $((a=c+d)) # discard the output of the arith expn with `:` command
[ $((d)) -ne 0 ] && echo d is true. # manually check non-zero => true
select
loops
It takes extra care over terminal columns to make select loop look like bash's, which generates a list with multiple items on one line, or like ls
.
It is, however, still possible to make a naive translation for select foo in bar baz; do eat; done
:
while
_i=0 _foo= foo=
for _name in bar baz; do echo "$((_i+=1))) $_name"; done
printf '$# '; read _foo
do
case _foo in 1) foo=bar;; 2) foo=baz;; *) continue;; esac
eat
done
Here-strings
Bash, ksh:
grep aaa <<< "$g"
POSIX:
# not exactly the same -- <<< adds a trailing \n if $g doesn't end with \n
printf '%s' "$g" | grep aaa
echo flags
See https://unix.stackexchange.com/tags/echo/info.
${var/pat/replacement}
Bash:
echo "${TERM/%-256*}"
POSIX:
echo "$TERM" | sed -e 's/-256.*$//g'
# Special case for this since we are matching the end:
echo "${TERM%-256*}"
printf %q
Bash:
printf '%q ' "$@"
POSIX:
# TODO: Interpret it back to printf escapes for hard-to-copy chars like \t?
# See also: http://git.savannah.gnu.org/cgit/libtool.git/tree/gl/build-aux/funclib.sh?id=c60e054#n1029
reuse_quote()(
for i; do
__i_quote=$(printf '%s\n' "$i" | sed -e "s/'/'\\\\''/g"; echo x)
printf "'%s'" "${__i_quote%x}"
done
)
reuse_quote "$@"
Exception
Depends on what your expected POSIX shell providers would use.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
In POSIX sh, named file descriptors are undefined. Open
if ( exec {fd}>/dev/null ) 2>/dev/null; then
- Read upRead up
- Exclude checks
In POSIX sh, something is undefined.
You have declared that your script works with /bin/sh
, but you are using features that have undefined behavior according to the POSIX specification.
It may currently work for you, but it can or will fail on other OS, the same OS with different configurations, from different contexts (like initramfs/chroot), or in different versions of the same OS, including future updates to your current system.
Either declare that your script requires a specific shell like #!/bin/bash
or #!/bin/dash
, or rewrite the script in a portable way.
For help with rewrites, the Ubuntu wiki has a list of portability issues that broke people's #!/bin/sh
scripts when Ubuntu switched from Bash to Dash. See also Bashism on wooledge's wiki. ShellCheck may not warn about all these issues.
$'c-style-escapes'
bash, ksh:
a=$' \t\n'
POSIX:
a="$(printf '%b_' ' \t\n')"; a="${a%_}" # protect trailing \n
Want some good news? See http://austingroupbugs.net/view.php?id=249#c590.
$"msgid"
Bash:
echo $"foo $(bar) baz"
POSIX:
. gettext.sh # GNU Gettext sh library
# ...
barout=$(bar)
eval_gettext 'foo $barout baz' # See GNU Gettext doc for more info.
Or you can change them to normal double quotes so you go without gettext
.
Arithmetic for
loops
Bash:
for ((init; test; next)); do foo; done
POSIX:
: $((init))
while [ $((test)) -ne 0 ]; do foo; : $((next)); done
Arithmetic exponentiation
Bash:
printf "%s\n" "$(( 2**63 ))"
POSIX:
The POSIX standard does not allow for exponents. However, you can replicate them completely built-in using a POSIX compatible function. As an example, the pow
function from here.
pow () {
set "$1" "$2" 1
while [ "$2" -gt 0 ]; do
set "$1" $(($2-1)) $(($1*$3))
done
# %d = signed decimal, %u = unsigned decimal
# Either should overflow to 0
printf "%d\n" "$3"
}
To compare:
$ echo "$(( 2**62 ))"
4611686018427387904
$ pow 2 62
4611686018427387904
Alternatively, if you don't mind using an external program, you can use bc
. Be aware though: bash
and other programs may abide by a certain maximum integer that bc
does not (for bash
that's: 64-bit signed long int, failing back to 32-bit signed long int).
Example:
# Note the overflow that gives a negative number
$ echo "$(( 2**63 ))"
-9223372036854775808
# No such problem
$ echo 2^63 | bc
9223372036854775808
# 'bc' just keeps on going
$ echo 2^1280 | bc
20815864389328798163850480654728171077230524494533409610638224700807\
21611934672059602447888346464836968484322790856201558276713249664692\
98162798132113546415258482590187784406915463666993231671009459188410\
95379622423387354295096957733925002768876520583464697770622321657076\
83317005651120933244966378183760369413644440628104205339687097746591\
6057756101739472373801429441421111406337458176
standalone ((..))
Bash:
((a=c+d))
((d)) && echo d is true.
POSIX:
: $((a=c+d)) # discard the output of the arith expn with `:` command
[ $((d)) -ne 0 ] && echo d is true. # manually check non-zero => true
select
loops
It takes extra care over terminal columns to make select loop look like bash's, which generates a list with multiple items on one line, or like ls
.
It is, however, still possible to make a naive translation for select foo in bar baz; do eat; done
:
while
_i=0 _foo= foo=
for _name in bar baz; do echo "$((_i+=1))) $_name"; done
printf '$# '; read _foo
do
case _foo in 1) foo=bar;; 2) foo=baz;; *) continue;; esac
eat
done
Here-strings
Bash, ksh:
grep aaa <<< "$g"
POSIX:
# not exactly the same -- <<< adds a trailing \n if $g doesn't end with \n
printf '%s' "$g" | grep aaa
echo flags
See https://unix.stackexchange.com/tags/echo/info.
${var/pat/replacement}
Bash:
echo "${TERM/%-256*}"
POSIX:
echo "$TERM" | sed -e 's/-256.*$//g'
# Special case for this since we are matching the end:
echo "${TERM%-256*}"
printf %q
Bash:
printf '%q ' "$@"
POSIX:
# TODO: Interpret it back to printf escapes for hard-to-copy chars like \t?
# See also: http://git.savannah.gnu.org/cgit/libtool.git/tree/gl/build-aux/funclib.sh?id=c60e054#n1029
reuse_quote()(
for i; do
__i_quote=$(printf '%s\n' "$i" | sed -e "s/'/'\\\\''/g"; echo x)
printf "'%s'" "${__i_quote%x}"
done
)
reuse_quote "$@"
Exception
Depends on what your expected POSIX shell providers would use.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
In POSIX sh, 'typeset' is undefined. Open
eval "$(typeset -p IFS)"
- Read upRead up
- Exclude checks
In POSIX sh, something is undefined.
You have declared that your script works with /bin/sh
, but you are using features that have undefined behavior according to the POSIX specification.
It may currently work for you, but it can or will fail on other OS, the same OS with different configurations, from different contexts (like initramfs/chroot), or in different versions of the same OS, including future updates to your current system.
Either declare that your script requires a specific shell like #!/bin/bash
or #!/bin/dash
, or rewrite the script in a portable way.
For help with rewrites, the Ubuntu wiki has a list of portability issues that broke people's #!/bin/sh
scripts when Ubuntu switched from Bash to Dash. See also Bashism on wooledge's wiki. ShellCheck may not warn about all these issues.
$'c-style-escapes'
bash, ksh:
a=$' \t\n'
POSIX:
a="$(printf '%b_' ' \t\n')"; a="${a%_}" # protect trailing \n
Want some good news? See http://austingroupbugs.net/view.php?id=249#c590.
$"msgid"
Bash:
echo $"foo $(bar) baz"
POSIX:
. gettext.sh # GNU Gettext sh library
# ...
barout=$(bar)
eval_gettext 'foo $barout baz' # See GNU Gettext doc for more info.
Or you can change them to normal double quotes so you go without gettext
.
Arithmetic for
loops
Bash:
for ((init; test; next)); do foo; done
POSIX:
: $((init))
while [ $((test)) -ne 0 ]; do foo; : $((next)); done
Arithmetic exponentiation
Bash:
printf "%s\n" "$(( 2**63 ))"
POSIX:
The POSIX standard does not allow for exponents. However, you can replicate them completely built-in using a POSIX compatible function. As an example, the pow
function from here.
pow () {
set "$1" "$2" 1
while [ "$2" -gt 0 ]; do
set "$1" $(($2-1)) $(($1*$3))
done
# %d = signed decimal, %u = unsigned decimal
# Either should overflow to 0
printf "%d\n" "$3"
}
To compare:
$ echo "$(( 2**62 ))"
4611686018427387904
$ pow 2 62
4611686018427387904
Alternatively, if you don't mind using an external program, you can use bc
. Be aware though: bash
and other programs may abide by a certain maximum integer that bc
does not (for bash
that's: 64-bit signed long int, failing back to 32-bit signed long int).
Example:
# Note the overflow that gives a negative number
$ echo "$(( 2**63 ))"
-9223372036854775808
# No such problem
$ echo 2^63 | bc
9223372036854775808
# 'bc' just keeps on going
$ echo 2^1280 | bc
20815864389328798163850480654728171077230524494533409610638224700807\
21611934672059602447888346464836968484322790856201558276713249664692\
98162798132113546415258482590187784406915463666993231671009459188410\
95379622423387354295096957733925002768876520583464697770622321657076\
83317005651120933244966378183760369413644440628104205339687097746591\
6057756101739472373801429441421111406337458176
standalone ((..))
Bash:
((a=c+d))
((d)) && echo d is true.
POSIX:
: $((a=c+d)) # discard the output of the arith expn with `:` command
[ $((d)) -ne 0 ] && echo d is true. # manually check non-zero => true
select
loops
It takes extra care over terminal columns to make select loop look like bash's, which generates a list with multiple items on one line, or like ls
.
It is, however, still possible to make a naive translation for select foo in bar baz; do eat; done
:
while
_i=0 _foo= foo=
for _name in bar baz; do echo "$((_i+=1))) $_name"; done
printf '$# '; read _foo
do
case _foo in 1) foo=bar;; 2) foo=baz;; *) continue;; esac
eat
done
Here-strings
Bash, ksh:
grep aaa <<< "$g"
POSIX:
# not exactly the same -- <<< adds a trailing \n if $g doesn't end with \n
printf '%s' "$g" | grep aaa
echo flags
See https://unix.stackexchange.com/tags/echo/info.
${var/pat/replacement}
Bash:
echo "${TERM/%-256*}"
POSIX:
echo "$TERM" | sed -e 's/-256.*$//g'
# Special case for this since we are matching the end:
echo "${TERM%-256*}"
printf %q
Bash:
printf '%q ' "$@"
POSIX:
# TODO: Interpret it back to printf escapes for hard-to-copy chars like \t?
# See also: http://git.savannah.gnu.org/cgit/libtool.git/tree/gl/build-aux/funclib.sh?id=c60e054#n1029
reuse_quote()(
for i; do
__i_quote=$(printf '%s\n' "$i" | sed -e "s/'/'\\\\''/g"; echo x)
printf "'%s'" "${__i_quote%x}"
done
)
reuse_quote "$@"
Exception
Depends on what your expected POSIX shell providers would use.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
In POSIX sh, trapping DEBUG is undefined. Open
trap ':' DEBUG
- Read upRead up
- Exclude checks
In POSIX sh, something is undefined.
You have declared that your script works with /bin/sh
, but you are using features that have undefined behavior according to the POSIX specification.
It may currently work for you, but it can or will fail on other OS, the same OS with different configurations, from different contexts (like initramfs/chroot), or in different versions of the same OS, including future updates to your current system.
Either declare that your script requires a specific shell like #!/bin/bash
or #!/bin/dash
, or rewrite the script in a portable way.
For help with rewrites, the Ubuntu wiki has a list of portability issues that broke people's #!/bin/sh
scripts when Ubuntu switched from Bash to Dash. See also Bashism on wooledge's wiki. ShellCheck may not warn about all these issues.
$'c-style-escapes'
bash, ksh:
a=$' \t\n'
POSIX:
a="$(printf '%b_' ' \t\n')"; a="${a%_}" # protect trailing \n
Want some good news? See http://austingroupbugs.net/view.php?id=249#c590.
$"msgid"
Bash:
echo $"foo $(bar) baz"
POSIX:
. gettext.sh # GNU Gettext sh library
# ...
barout=$(bar)
eval_gettext 'foo $barout baz' # See GNU Gettext doc for more info.
Or you can change them to normal double quotes so you go without gettext
.
Arithmetic for
loops
Bash:
for ((init; test; next)); do foo; done
POSIX:
: $((init))
while [ $((test)) -ne 0 ]; do foo; : $((next)); done
Arithmetic exponentiation
Bash:
printf "%s\n" "$(( 2**63 ))"
POSIX:
The POSIX standard does not allow for exponents. However, you can replicate them completely built-in using a POSIX compatible function. As an example, the pow
function from here.
pow () {
set "$1" "$2" 1
while [ "$2" -gt 0 ]; do
set "$1" $(($2-1)) $(($1*$3))
done
# %d = signed decimal, %u = unsigned decimal
# Either should overflow to 0
printf "%d\n" "$3"
}
To compare:
$ echo "$(( 2**62 ))"
4611686018427387904
$ pow 2 62
4611686018427387904
Alternatively, if you don't mind using an external program, you can use bc
. Be aware though: bash
and other programs may abide by a certain maximum integer that bc
does not (for bash
that's: 64-bit signed long int, failing back to 32-bit signed long int).
Example:
# Note the overflow that gives a negative number
$ echo "$(( 2**63 ))"
-9223372036854775808
# No such problem
$ echo 2^63 | bc
9223372036854775808
# 'bc' just keeps on going
$ echo 2^1280 | bc
20815864389328798163850480654728171077230524494533409610638224700807\
21611934672059602447888346464836968484322790856201558276713249664692\
98162798132113546415258482590187784406915463666993231671009459188410\
95379622423387354295096957733925002768876520583464697770622321657076\
83317005651120933244966378183760369413644440628104205339687097746591\
6057756101739472373801429441421111406337458176
standalone ((..))
Bash:
((a=c+d))
((d)) && echo d is true.
POSIX:
: $((a=c+d)) # discard the output of the arith expn with `:` command
[ $((d)) -ne 0 ] && echo d is true. # manually check non-zero => true
select
loops
It takes extra care over terminal columns to make select loop look like bash's, which generates a list with multiple items on one line, or like ls
.
It is, however, still possible to make a naive translation for select foo in bar baz; do eat; done
:
while
_i=0 _foo= foo=
for _name in bar baz; do echo "$((_i+=1))) $_name"; done
printf '$# '; read _foo
do
case _foo in 1) foo=bar;; 2) foo=baz;; *) continue;; esac
eat
done
Here-strings
Bash, ksh:
grep aaa <<< "$g"
POSIX:
# not exactly the same -- <<< adds a trailing \n if $g doesn't end with \n
printf '%s' "$g" | grep aaa
echo flags
See https://unix.stackexchange.com/tags/echo/info.
${var/pat/replacement}
Bash:
echo "${TERM/%-256*}"
POSIX:
echo "$TERM" | sed -e 's/-256.*$//g'
# Special case for this since we are matching the end:
echo "${TERM%-256*}"
printf %q
Bash:
printf '%q ' "$@"
POSIX:
# TODO: Interpret it back to printf escapes for hard-to-copy chars like \t?
# See also: http://git.savannah.gnu.org/cgit/libtool.git/tree/gl/build-aux/funclib.sh?id=c60e054#n1029
reuse_quote()(
for i; do
__i_quote=$(printf '%s\n' "$i" | sed -e "s/'/'\\\\''/g"; echo x)
printf "'%s'" "${__i_quote%x}"
done
)
reuse_quote "$@"
Exception
Depends on what your expected POSIX shell providers would use.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
In POSIX sh, 'type' is undefined. Open
if type shopt >/dev/null 2>&1; then
- Read upRead up
- Exclude checks
In POSIX sh, something is undefined.
You have declared that your script works with /bin/sh
, but you are using features that have undefined behavior according to the POSIX specification.
It may currently work for you, but it can or will fail on other OS, the same OS with different configurations, from different contexts (like initramfs/chroot), or in different versions of the same OS, including future updates to your current system.
Either declare that your script requires a specific shell like #!/bin/bash
or #!/bin/dash
, or rewrite the script in a portable way.
For help with rewrites, the Ubuntu wiki has a list of portability issues that broke people's #!/bin/sh
scripts when Ubuntu switched from Bash to Dash. See also Bashism on wooledge's wiki. ShellCheck may not warn about all these issues.
$'c-style-escapes'
bash, ksh:
a=$' \t\n'
POSIX:
a="$(printf '%b_' ' \t\n')"; a="${a%_}" # protect trailing \n
Want some good news? See http://austingroupbugs.net/view.php?id=249#c590.
$"msgid"
Bash:
echo $"foo $(bar) baz"
POSIX:
. gettext.sh # GNU Gettext sh library
# ...
barout=$(bar)
eval_gettext 'foo $barout baz' # See GNU Gettext doc for more info.
Or you can change them to normal double quotes so you go without gettext
.
Arithmetic for
loops
Bash:
for ((init; test; next)); do foo; done
POSIX:
: $((init))
while [ $((test)) -ne 0 ]; do foo; : $((next)); done
Arithmetic exponentiation
Bash:
printf "%s\n" "$(( 2**63 ))"
POSIX:
The POSIX standard does not allow for exponents. However, you can replicate them completely built-in using a POSIX compatible function. As an example, the pow
function from here.
pow () {
set "$1" "$2" 1
while [ "$2" -gt 0 ]; do
set "$1" $(($2-1)) $(($1*$3))
done
# %d = signed decimal, %u = unsigned decimal
# Either should overflow to 0
printf "%d\n" "$3"
}
To compare:
$ echo "$(( 2**62 ))"
4611686018427387904
$ pow 2 62
4611686018427387904
Alternatively, if you don't mind using an external program, you can use bc
. Be aware though: bash
and other programs may abide by a certain maximum integer that bc
does not (for bash
that's: 64-bit signed long int, failing back to 32-bit signed long int).
Example:
# Note the overflow that gives a negative number
$ echo "$(( 2**63 ))"
-9223372036854775808
# No such problem
$ echo 2^63 | bc
9223372036854775808
# 'bc' just keeps on going
$ echo 2^1280 | bc
20815864389328798163850480654728171077230524494533409610638224700807\
21611934672059602447888346464836968484322790856201558276713249664692\
98162798132113546415258482590187784406915463666993231671009459188410\
95379622423387354295096957733925002768876520583464697770622321657076\
83317005651120933244966378183760369413644440628104205339687097746591\
6057756101739472373801429441421111406337458176
standalone ((..))
Bash:
((a=c+d))
((d)) && echo d is true.
POSIX:
: $((a=c+d)) # discard the output of the arith expn with `:` command
[ $((d)) -ne 0 ] && echo d is true. # manually check non-zero => true
select
loops
It takes extra care over terminal columns to make select loop look like bash's, which generates a list with multiple items on one line, or like ls
.
It is, however, still possible to make a naive translation for select foo in bar baz; do eat; done
:
while
_i=0 _foo= foo=
for _name in bar baz; do echo "$((_i+=1))) $_name"; done
printf '$# '; read _foo
do
case _foo in 1) foo=bar;; 2) foo=baz;; *) continue;; esac
eat
done
Here-strings
Bash, ksh:
grep aaa <<< "$g"
POSIX:
# not exactly the same -- <<< adds a trailing \n if $g doesn't end with \n
printf '%s' "$g" | grep aaa
echo flags
See https://unix.stackexchange.com/tags/echo/info.
${var/pat/replacement}
Bash:
echo "${TERM/%-256*}"
POSIX:
echo "$TERM" | sed -e 's/-256.*$//g'
# Special case for this since we are matching the end:
echo "${TERM%-256*}"
printf %q
Bash:
printf '%q ' "$@"
POSIX:
# TODO: Interpret it back to printf escapes for hard-to-copy chars like \t?
# See also: http://git.savannah.gnu.org/cgit/libtool.git/tree/gl/build-aux/funclib.sh?id=c60e054#n1029
reuse_quote()(
for i; do
__i_quote=$(printf '%s\n' "$i" | sed -e "s/'/'\\\\''/g"; echo x)
printf "'%s'" "${__i_quote%x}"
done
)
reuse_quote "$@"
Exception
Depends on what your expected POSIX shell providers would use.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
var appears unused. Verify it or export it. Open
set -- "$(var=data; typeset -p var 2>/dev/null ||:)" ||:
- Read upRead up
- Exclude checks
foo appears unused. Verify it or export it.
Problematic code:
foo=42
echo "$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.
In POSIX sh, 'typeset' is undefined. Open
elif ( typeset -r .sh >/dev/null 2>&1 ); then
- Read upRead up
- Exclude checks
In POSIX sh, something is undefined.
You have declared that your script works with /bin/sh
, but you are using features that have undefined behavior according to the POSIX specification.
It may currently work for you, but it can or will fail on other OS, the same OS with different configurations, from different contexts (like initramfs/chroot), or in different versions of the same OS, including future updates to your current system.
Either declare that your script requires a specific shell like #!/bin/bash
or #!/bin/dash
, or rewrite the script in a portable way.
For help with rewrites, the Ubuntu wiki has a list of portability issues that broke people's #!/bin/sh
scripts when Ubuntu switched from Bash to Dash. See also Bashism on wooledge's wiki. ShellCheck may not warn about all these issues.
$'c-style-escapes'
bash, ksh:
a=$' \t\n'
POSIX:
a="$(printf '%b_' ' \t\n')"; a="${a%_}" # protect trailing \n
Want some good news? See http://austingroupbugs.net/view.php?id=249#c590.
$"msgid"
Bash:
echo $"foo $(bar) baz"
POSIX:
. gettext.sh # GNU Gettext sh library
# ...
barout=$(bar)
eval_gettext 'foo $barout baz' # See GNU Gettext doc for more info.
Or you can change them to normal double quotes so you go without gettext
.
Arithmetic for
loops
Bash:
for ((init; test; next)); do foo; done
POSIX:
: $((init))
while [ $((test)) -ne 0 ]; do foo; : $((next)); done
Arithmetic exponentiation
Bash:
printf "%s\n" "$(( 2**63 ))"
POSIX:
The POSIX standard does not allow for exponents. However, you can replicate them completely built-in using a POSIX compatible function. As an example, the pow
function from here.
pow () {
set "$1" "$2" 1
while [ "$2" -gt 0 ]; do
set "$1" $(($2-1)) $(($1*$3))
done
# %d = signed decimal, %u = unsigned decimal
# Either should overflow to 0
printf "%d\n" "$3"
}
To compare:
$ echo "$(( 2**62 ))"
4611686018427387904
$ pow 2 62
4611686018427387904
Alternatively, if you don't mind using an external program, you can use bc
. Be aware though: bash
and other programs may abide by a certain maximum integer that bc
does not (for bash
that's: 64-bit signed long int, failing back to 32-bit signed long int).
Example:
# Note the overflow that gives a negative number
$ echo "$(( 2**63 ))"
-9223372036854775808
# No such problem
$ echo 2^63 | bc
9223372036854775808
# 'bc' just keeps on going
$ echo 2^1280 | bc
20815864389328798163850480654728171077230524494533409610638224700807\
21611934672059602447888346464836968484322790856201558276713249664692\
98162798132113546415258482590187784406915463666993231671009459188410\
95379622423387354295096957733925002768876520583464697770622321657076\
83317005651120933244966378183760369413644440628104205339687097746591\
6057756101739472373801429441421111406337458176
standalone ((..))
Bash:
((a=c+d))
((d)) && echo d is true.
POSIX:
: $((a=c+d)) # discard the output of the arith expn with `:` command
[ $((d)) -ne 0 ] && echo d is true. # manually check non-zero => true
select
loops
It takes extra care over terminal columns to make select loop look like bash's, which generates a list with multiple items on one line, or like ls
.
It is, however, still possible to make a naive translation for select foo in bar baz; do eat; done
:
while
_i=0 _foo= foo=
for _name in bar baz; do echo "$((_i+=1))) $_name"; done
printf '$# '; read _foo
do
case _foo in 1) foo=bar;; 2) foo=baz;; *) continue;; esac
eat
done
Here-strings
Bash, ksh:
grep aaa <<< "$g"
POSIX:
# not exactly the same -- <<< adds a trailing \n if $g doesn't end with \n
printf '%s' "$g" | grep aaa
echo flags
See https://unix.stackexchange.com/tags/echo/info.
${var/pat/replacement}
Bash:
echo "${TERM/%-256*}"
POSIX:
echo "$TERM" | sed -e 's/-256.*$//g'
# Special case for this since we are matching the end:
echo "${TERM%-256*}"
printf %q
Bash:
printf '%q ' "$@"
POSIX:
# TODO: Interpret it back to printf escapes for hard-to-copy chars like \t?
# See also: http://git.savannah.gnu.org/cgit/libtool.git/tree/gl/build-aux/funclib.sh?id=c60e054#n1029
reuse_quote()(
for i; do
__i_quote=$(printf '%s\n' "$i" | sed -e "s/'/'\\\\''/g"; echo x)
printf "'%s'" "${__i_quote%x}"
done
)
reuse_quote "$@"
Exception
Depends on what your expected POSIX shell providers would use.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
In POSIX sh, += is undefined. Open
if string+="concat" 2>/dev/null; then
- Read upRead up
- Exclude checks
In POSIX sh, something is undefined.
You have declared that your script works with /bin/sh
, but you are using features that have undefined behavior according to the POSIX specification.
It may currently work for you, but it can or will fail on other OS, the same OS with different configurations, from different contexts (like initramfs/chroot), or in different versions of the same OS, including future updates to your current system.
Either declare that your script requires a specific shell like #!/bin/bash
or #!/bin/dash
, or rewrite the script in a portable way.
For help with rewrites, the Ubuntu wiki has a list of portability issues that broke people's #!/bin/sh
scripts when Ubuntu switched from Bash to Dash. See also Bashism on wooledge's wiki. ShellCheck may not warn about all these issues.
$'c-style-escapes'
bash, ksh:
a=$' \t\n'
POSIX:
a="$(printf '%b_' ' \t\n')"; a="${a%_}" # protect trailing \n
Want some good news? See http://austingroupbugs.net/view.php?id=249#c590.
$"msgid"
Bash:
echo $"foo $(bar) baz"
POSIX:
. gettext.sh # GNU Gettext sh library
# ...
barout=$(bar)
eval_gettext 'foo $barout baz' # See GNU Gettext doc for more info.
Or you can change them to normal double quotes so you go without gettext
.
Arithmetic for
loops
Bash:
for ((init; test; next)); do foo; done
POSIX:
: $((init))
while [ $((test)) -ne 0 ]; do foo; : $((next)); done
Arithmetic exponentiation
Bash:
printf "%s\n" "$(( 2**63 ))"
POSIX:
The POSIX standard does not allow for exponents. However, you can replicate them completely built-in using a POSIX compatible function. As an example, the pow
function from here.
pow () {
set "$1" "$2" 1
while [ "$2" -gt 0 ]; do
set "$1" $(($2-1)) $(($1*$3))
done
# %d = signed decimal, %u = unsigned decimal
# Either should overflow to 0
printf "%d\n" "$3"
}
To compare:
$ echo "$(( 2**62 ))"
4611686018427387904
$ pow 2 62
4611686018427387904
Alternatively, if you don't mind using an external program, you can use bc
. Be aware though: bash
and other programs may abide by a certain maximum integer that bc
does not (for bash
that's: 64-bit signed long int, failing back to 32-bit signed long int).
Example:
# Note the overflow that gives a negative number
$ echo "$(( 2**63 ))"
-9223372036854775808
# No such problem
$ echo 2^63 | bc
9223372036854775808
# 'bc' just keeps on going
$ echo 2^1280 | bc
20815864389328798163850480654728171077230524494533409610638224700807\
21611934672059602447888346464836968484322790856201558276713249664692\
98162798132113546415258482590187784406915463666993231671009459188410\
95379622423387354295096957733925002768876520583464697770622321657076\
83317005651120933244966378183760369413644440628104205339687097746591\
6057756101739472373801429441421111406337458176
standalone ((..))
Bash:
((a=c+d))
((d)) && echo d is true.
POSIX:
: $((a=c+d)) # discard the output of the arith expn with `:` command
[ $((d)) -ne 0 ] && echo d is true. # manually check non-zero => true
select
loops
It takes extra care over terminal columns to make select loop look like bash's, which generates a list with multiple items on one line, or like ls
.
It is, however, still possible to make a naive translation for select foo in bar baz; do eat; done
:
while
_i=0 _foo= foo=
for _name in bar baz; do echo "$((_i+=1))) $_name"; done
printf '$# '; read _foo
do
case _foo in 1) foo=bar;; 2) foo=baz;; *) continue;; esac
eat
done
Here-strings
Bash, ksh:
grep aaa <<< "$g"
POSIX:
# not exactly the same -- <<< adds a trailing \n if $g doesn't end with \n
printf '%s' "$g" | grep aaa
echo flags
See https://unix.stackexchange.com/tags/echo/info.
${var/pat/replacement}
Bash:
echo "${TERM/%-256*}"
POSIX:
echo "$TERM" | sed -e 's/-256.*$//g'
# Special case for this since we are matching the end:
echo "${TERM%-256*}"
printf %q
Bash:
printf '%q ' "$@"
POSIX:
# TODO: Interpret it back to printf escapes for hard-to-copy chars like \t?
# See also: http://git.savannah.gnu.org/cgit/libtool.git/tree/gl/build-aux/funclib.sh?id=c60e054#n1029
reuse_quote()(
for i; do
__i_quote=$(printf '%s\n' "$i" | sed -e "s/'/'\\\\''/g"; echo x)
printf "'%s'" "${__i_quote%x}"
done
)
reuse_quote "$@"
Exception
Depends on what your expected POSIX shell providers would use.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
In POSIX sh, 'typeset' is undefined. Open
if typeset >/dev/null 2>&1; then
- Read upRead up
- Exclude checks
In POSIX sh, something is undefined.
You have declared that your script works with /bin/sh
, but you are using features that have undefined behavior according to the POSIX specification.
It may currently work for you, but it can or will fail on other OS, the same OS with different configurations, from different contexts (like initramfs/chroot), or in different versions of the same OS, including future updates to your current system.
Either declare that your script requires a specific shell like #!/bin/bash
or #!/bin/dash
, or rewrite the script in a portable way.
For help with rewrites, the Ubuntu wiki has a list of portability issues that broke people's #!/bin/sh
scripts when Ubuntu switched from Bash to Dash. See also Bashism on wooledge's wiki. ShellCheck may not warn about all these issues.
$'c-style-escapes'
bash, ksh:
a=$' \t\n'
POSIX:
a="$(printf '%b_' ' \t\n')"; a="${a%_}" # protect trailing \n
Want some good news? See http://austingroupbugs.net/view.php?id=249#c590.
$"msgid"
Bash:
echo $"foo $(bar) baz"
POSIX:
. gettext.sh # GNU Gettext sh library
# ...
barout=$(bar)
eval_gettext 'foo $barout baz' # See GNU Gettext doc for more info.
Or you can change them to normal double quotes so you go without gettext
.
Arithmetic for
loops
Bash:
for ((init; test; next)); do foo; done
POSIX:
: $((init))
while [ $((test)) -ne 0 ]; do foo; : $((next)); done
Arithmetic exponentiation
Bash:
printf "%s\n" "$(( 2**63 ))"
POSIX:
The POSIX standard does not allow for exponents. However, you can replicate them completely built-in using a POSIX compatible function. As an example, the pow
function from here.
pow () {
set "$1" "$2" 1
while [ "$2" -gt 0 ]; do
set "$1" $(($2-1)) $(($1*$3))
done
# %d = signed decimal, %u = unsigned decimal
# Either should overflow to 0
printf "%d\n" "$3"
}
To compare:
$ echo "$(( 2**62 ))"
4611686018427387904
$ pow 2 62
4611686018427387904
Alternatively, if you don't mind using an external program, you can use bc
. Be aware though: bash
and other programs may abide by a certain maximum integer that bc
does not (for bash
that's: 64-bit signed long int, failing back to 32-bit signed long int).
Example:
# Note the overflow that gives a negative number
$ echo "$(( 2**63 ))"
-9223372036854775808
# No such problem
$ echo 2^63 | bc
9223372036854775808
# 'bc' just keeps on going
$ echo 2^1280 | bc
20815864389328798163850480654728171077230524494533409610638224700807\
21611934672059602447888346464836968484322790856201558276713249664692\
98162798132113546415258482590187784406915463666993231671009459188410\
95379622423387354295096957733925002768876520583464697770622321657076\
83317005651120933244966378183760369413644440628104205339687097746591\
6057756101739472373801429441421111406337458176
standalone ((..))
Bash:
((a=c+d))
((d)) && echo d is true.
POSIX:
: $((a=c+d)) # discard the output of the arith expn with `:` command
[ $((d)) -ne 0 ] && echo d is true. # manually check non-zero => true
select
loops
It takes extra care over terminal columns to make select loop look like bash's, which generates a list with multiple items on one line, or like ls
.
It is, however, still possible to make a naive translation for select foo in bar baz; do eat; done
:
while
_i=0 _foo= foo=
for _name in bar baz; do echo "$((_i+=1))) $_name"; done
printf '$# '; read _foo
do
case _foo in 1) foo=bar;; 2) foo=baz;; *) continue;; esac
eat
done
Here-strings
Bash, ksh:
grep aaa <<< "$g"
POSIX:
# not exactly the same -- <<< adds a trailing \n if $g doesn't end with \n
printf '%s' "$g" | grep aaa
echo flags
See https://unix.stackexchange.com/tags/echo/info.
${var/pat/replacement}
Bash:
echo "${TERM/%-256*}"
POSIX:
echo "$TERM" | sed -e 's/-256.*$//g'
# Special case for this since we are matching the end:
echo "${TERM%-256*}"
printf %q
Bash:
printf '%q ' "$@"
POSIX:
# TODO: Interpret it back to printf escapes for hard-to-copy chars like \t?
# See also: http://git.savannah.gnu.org/cgit/libtool.git/tree/gl/build-aux/funclib.sh?id=c60e054#n1029
reuse_quote()(
for i; do
__i_quote=$(printf '%s\n' "$i" | sed -e "s/'/'\\\\''/g"; echo x)
printf "'%s'" "${__i_quote%x}"
done
)
reuse_quote "$@"
Exception
Depends on what your expected POSIX shell providers would use.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
typesetf_check appears unused. Verify it or export it. Open
if typeset -f typesetf_check >/dev/null 2>&1; then
- 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.
In POSIX sh, 'typeset' is undefined. Open
if typeset -f typesetf_check >/dev/null 2>&1; then
- Read upRead up
- Exclude checks
In POSIX sh, something is undefined.
You have declared that your script works with /bin/sh
, but you are using features that have undefined behavior according to the POSIX specification.
It may currently work for you, but it can or will fail on other OS, the same OS with different configurations, from different contexts (like initramfs/chroot), or in different versions of the same OS, including future updates to your current system.
Either declare that your script requires a specific shell like #!/bin/bash
or #!/bin/dash
, or rewrite the script in a portable way.
For help with rewrites, the Ubuntu wiki has a list of portability issues that broke people's #!/bin/sh
scripts when Ubuntu switched from Bash to Dash. See also Bashism on wooledge's wiki. ShellCheck may not warn about all these issues.
$'c-style-escapes'
bash, ksh:
a=$' \t\n'
POSIX:
a="$(printf '%b_' ' \t\n')"; a="${a%_}" # protect trailing \n
Want some good news? See http://austingroupbugs.net/view.php?id=249#c590.
$"msgid"
Bash:
echo $"foo $(bar) baz"
POSIX:
. gettext.sh # GNU Gettext sh library
# ...
barout=$(bar)
eval_gettext 'foo $barout baz' # See GNU Gettext doc for more info.
Or you can change them to normal double quotes so you go without gettext
.
Arithmetic for
loops
Bash:
for ((init; test; next)); do foo; done
POSIX:
: $((init))
while [ $((test)) -ne 0 ]; do foo; : $((next)); done
Arithmetic exponentiation
Bash:
printf "%s\n" "$(( 2**63 ))"
POSIX:
The POSIX standard does not allow for exponents. However, you can replicate them completely built-in using a POSIX compatible function. As an example, the pow
function from here.
pow () {
set "$1" "$2" 1
while [ "$2" -gt 0 ]; do
set "$1" $(($2-1)) $(($1*$3))
done
# %d = signed decimal, %u = unsigned decimal
# Either should overflow to 0
printf "%d\n" "$3"
}
To compare:
$ echo "$(( 2**62 ))"
4611686018427387904
$ pow 2 62
4611686018427387904
Alternatively, if you don't mind using an external program, you can use bc
. Be aware though: bash
and other programs may abide by a certain maximum integer that bc
does not (for bash
that's: 64-bit signed long int, failing back to 32-bit signed long int).
Example:
# Note the overflow that gives a negative number
$ echo "$(( 2**63 ))"
-9223372036854775808
# No such problem
$ echo 2^63 | bc
9223372036854775808
# 'bc' just keeps on going
$ echo 2^1280 | bc
20815864389328798163850480654728171077230524494533409610638224700807\
21611934672059602447888346464836968484322790856201558276713249664692\
98162798132113546415258482590187784406915463666993231671009459188410\
95379622423387354295096957733925002768876520583464697770622321657076\
83317005651120933244966378183760369413644440628104205339687097746591\
6057756101739472373801429441421111406337458176
standalone ((..))
Bash:
((a=c+d))
((d)) && echo d is true.
POSIX:
: $((a=c+d)) # discard the output of the arith expn with `:` command
[ $((d)) -ne 0 ] && echo d is true. # manually check non-zero => true
select
loops
It takes extra care over terminal columns to make select loop look like bash's, which generates a list with multiple items on one line, or like ls
.
It is, however, still possible to make a naive translation for select foo in bar baz; do eat; done
:
while
_i=0 _foo= foo=
for _name in bar baz; do echo "$((_i+=1))) $_name"; done
printf '$# '; read _foo
do
case _foo in 1) foo=bar;; 2) foo=baz;; *) continue;; esac
eat
done
Here-strings
Bash, ksh:
grep aaa <<< "$g"
POSIX:
# not exactly the same -- <<< adds a trailing \n if $g doesn't end with \n
printf '%s' "$g" | grep aaa
echo flags
See https://unix.stackexchange.com/tags/echo/info.
${var/pat/replacement}
Bash:
echo "${TERM/%-256*}"
POSIX:
echo "$TERM" | sed -e 's/-256.*$//g'
# Special case for this since we are matching the end:
echo "${TERM%-256*}"
printf %q
Bash:
printf '%q ' "$@"
POSIX:
# TODO: Interpret it back to printf escapes for hard-to-copy chars like \t?
# See also: http://git.savannah.gnu.org/cgit/libtool.git/tree/gl/build-aux/funclib.sh?id=c60e054#n1029
reuse_quote()(
for i; do
__i_quote=$(printf '%s\n' "$i" | sed -e "s/'/'\\\\''/g"; echo x)
printf "'%s'" "${__i_quote%x}"
done
)
reuse_quote "$@"
Exception
Depends on what your expected POSIX shell providers would use.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
In POSIX sh, read -d is undefined. Open
read -r -d "" line <<'HERE' 2>/dev/null ||:
- Read upRead up
- Exclude checks
In POSIX sh, something is undefined.
You have declared that your script works with /bin/sh
, but you are using features that have undefined behavior according to the POSIX specification.
It may currently work for you, but it can or will fail on other OS, the same OS with different configurations, from different contexts (like initramfs/chroot), or in different versions of the same OS, including future updates to your current system.
Either declare that your script requires a specific shell like #!/bin/bash
or #!/bin/dash
, or rewrite the script in a portable way.
For help with rewrites, the Ubuntu wiki has a list of portability issues that broke people's #!/bin/sh
scripts when Ubuntu switched from Bash to Dash. See also Bashism on wooledge's wiki. ShellCheck may not warn about all these issues.
$'c-style-escapes'
bash, ksh:
a=$' \t\n'
POSIX:
a="$(printf '%b_' ' \t\n')"; a="${a%_}" # protect trailing \n
Want some good news? See http://austingroupbugs.net/view.php?id=249#c590.
$"msgid"
Bash:
echo $"foo $(bar) baz"
POSIX:
. gettext.sh # GNU Gettext sh library
# ...
barout=$(bar)
eval_gettext 'foo $barout baz' # See GNU Gettext doc for more info.
Or you can change them to normal double quotes so you go without gettext
.
Arithmetic for
loops
Bash:
for ((init; test; next)); do foo; done
POSIX:
: $((init))
while [ $((test)) -ne 0 ]; do foo; : $((next)); done
Arithmetic exponentiation
Bash:
printf "%s\n" "$(( 2**63 ))"
POSIX:
The POSIX standard does not allow for exponents. However, you can replicate them completely built-in using a POSIX compatible function. As an example, the pow
function from here.
pow () {
set "$1" "$2" 1
while [ "$2" -gt 0 ]; do
set "$1" $(($2-1)) $(($1*$3))
done
# %d = signed decimal, %u = unsigned decimal
# Either should overflow to 0
printf "%d\n" "$3"
}
To compare:
$ echo "$(( 2**62 ))"
4611686018427387904
$ pow 2 62
4611686018427387904
Alternatively, if you don't mind using an external program, you can use bc
. Be aware though: bash
and other programs may abide by a certain maximum integer that bc
does not (for bash
that's: 64-bit signed long int, failing back to 32-bit signed long int).
Example:
# Note the overflow that gives a negative number
$ echo "$(( 2**63 ))"
-9223372036854775808
# No such problem
$ echo 2^63 | bc
9223372036854775808
# 'bc' just keeps on going
$ echo 2^1280 | bc
20815864389328798163850480654728171077230524494533409610638224700807\
21611934672059602447888346464836968484322790856201558276713249664692\
98162798132113546415258482590187784406915463666993231671009459188410\
95379622423387354295096957733925002768876520583464697770622321657076\
83317005651120933244966378183760369413644440628104205339687097746591\
6057756101739472373801429441421111406337458176
standalone ((..))
Bash:
((a=c+d))
((d)) && echo d is true.
POSIX:
: $((a=c+d)) # discard the output of the arith expn with `:` command
[ $((d)) -ne 0 ] && echo d is true. # manually check non-zero => true
select
loops
It takes extra care over terminal columns to make select loop look like bash's, which generates a list with multiple items on one line, or like ls
.
It is, however, still possible to make a naive translation for select foo in bar baz; do eat; done
:
while
_i=0 _foo= foo=
for _name in bar baz; do echo "$((_i+=1))) $_name"; done
printf '$# '; read _foo
do
case _foo in 1) foo=bar;; 2) foo=baz;; *) continue;; esac
eat
done
Here-strings
Bash, ksh:
grep aaa <<< "$g"
POSIX:
# not exactly the same -- <<< adds a trailing \n if $g doesn't end with \n
printf '%s' "$g" | grep aaa
echo flags
See https://unix.stackexchange.com/tags/echo/info.
${var/pat/replacement}
Bash:
echo "${TERM/%-256*}"
POSIX:
echo "$TERM" | sed -e 's/-256.*$//g'
# Special case for this since we are matching the end:
echo "${TERM%-256*}"
printf %q
Bash:
printf '%q ' "$@"
POSIX:
# TODO: Interpret it back to printf escapes for hard-to-copy chars like \t?
# See also: http://git.savannah.gnu.org/cgit/libtool.git/tree/gl/build-aux/funclib.sh?id=c60e054#n1029
reuse_quote()(
for i; do
__i_quote=$(printf '%s\n' "$i" | sed -e "s/'/'\\\\''/g"; echo x)
printf "'%s'" "${__i_quote%x}"
done
)
reuse_quote "$@"
Exception
Depends on what your expected POSIX shell providers would use.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.
In POSIX sh, 'type' is undefined. Open
type typeset >/dev/null 2>&1 && xtrace=2 || xtrace=1
- Read upRead up
- Exclude checks
In POSIX sh, something is undefined.
You have declared that your script works with /bin/sh
, but you are using features that have undefined behavior according to the POSIX specification.
It may currently work for you, but it can or will fail on other OS, the same OS with different configurations, from different contexts (like initramfs/chroot), or in different versions of the same OS, including future updates to your current system.
Either declare that your script requires a specific shell like #!/bin/bash
or #!/bin/dash
, or rewrite the script in a portable way.
For help with rewrites, the Ubuntu wiki has a list of portability issues that broke people's #!/bin/sh
scripts when Ubuntu switched from Bash to Dash. See also Bashism on wooledge's wiki. ShellCheck may not warn about all these issues.
$'c-style-escapes'
bash, ksh:
a=$' \t\n'
POSIX:
a="$(printf '%b_' ' \t\n')"; a="${a%_}" # protect trailing \n
Want some good news? See http://austingroupbugs.net/view.php?id=249#c590.
$"msgid"
Bash:
echo $"foo $(bar) baz"
POSIX:
. gettext.sh # GNU Gettext sh library
# ...
barout=$(bar)
eval_gettext 'foo $barout baz' # See GNU Gettext doc for more info.
Or you can change them to normal double quotes so you go without gettext
.
Arithmetic for
loops
Bash:
for ((init; test; next)); do foo; done
POSIX:
: $((init))
while [ $((test)) -ne 0 ]; do foo; : $((next)); done
Arithmetic exponentiation
Bash:
printf "%s\n" "$(( 2**63 ))"
POSIX:
The POSIX standard does not allow for exponents. However, you can replicate them completely built-in using a POSIX compatible function. As an example, the pow
function from here.
pow () {
set "$1" "$2" 1
while [ "$2" -gt 0 ]; do
set "$1" $(($2-1)) $(($1*$3))
done
# %d = signed decimal, %u = unsigned decimal
# Either should overflow to 0
printf "%d\n" "$3"
}
To compare:
$ echo "$(( 2**62 ))"
4611686018427387904
$ pow 2 62
4611686018427387904
Alternatively, if you don't mind using an external program, you can use bc
. Be aware though: bash
and other programs may abide by a certain maximum integer that bc
does not (for bash
that's: 64-bit signed long int, failing back to 32-bit signed long int).
Example:
# Note the overflow that gives a negative number
$ echo "$(( 2**63 ))"
-9223372036854775808
# No such problem
$ echo 2^63 | bc
9223372036854775808
# 'bc' just keeps on going
$ echo 2^1280 | bc
20815864389328798163850480654728171077230524494533409610638224700807\
21611934672059602447888346464836968484322790856201558276713249664692\
98162798132113546415258482590187784406915463666993231671009459188410\
95379622423387354295096957733925002768876520583464697770622321657076\
83317005651120933244966378183760369413644440628104205339687097746591\
6057756101739472373801429441421111406337458176
standalone ((..))
Bash:
((a=c+d))
((d)) && echo d is true.
POSIX:
: $((a=c+d)) # discard the output of the arith expn with `:` command
[ $((d)) -ne 0 ] && echo d is true. # manually check non-zero => true
select
loops
It takes extra care over terminal columns to make select loop look like bash's, which generates a list with multiple items on one line, or like ls
.
It is, however, still possible to make a naive translation for select foo in bar baz; do eat; done
:
while
_i=0 _foo= foo=
for _name in bar baz; do echo "$((_i+=1))) $_name"; done
printf '$# '; read _foo
do
case _foo in 1) foo=bar;; 2) foo=baz;; *) continue;; esac
eat
done
Here-strings
Bash, ksh:
grep aaa <<< "$g"
POSIX:
# not exactly the same -- <<< adds a trailing \n if $g doesn't end with \n
printf '%s' "$g" | grep aaa
echo flags
See https://unix.stackexchange.com/tags/echo/info.
${var/pat/replacement}
Bash:
echo "${TERM/%-256*}"
POSIX:
echo "$TERM" | sed -e 's/-256.*$//g'
# Special case for this since we are matching the end:
echo "${TERM%-256*}"
printf %q
Bash:
printf '%q ' "$@"
POSIX:
# TODO: Interpret it back to printf escapes for hard-to-copy chars like \t?
# See also: http://git.savannah.gnu.org/cgit/libtool.git/tree/gl/build-aux/funclib.sh?id=c60e054#n1029
reuse_quote()(
for i; do
__i_quote=$(printf '%s\n' "$i" | sed -e "s/'/'\\\\''/g"; echo x)
printf "'%s'" "${__i_quote%x}"
done
)
reuse_quote "$@"
Exception
Depends on what your expected POSIX shell providers would use.
Notice
Original content from the ShellCheck https://github.com/koalaman/shellcheck/wiki.