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| = How to make bash scripts work in dash = |
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| == Expansions | == Syntax == |
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| * Brace Expansion, eg {1..10} is not defined by posix | || || '''Works in bash''' || '''Change to for dash''' || '''Comment''' || || defining functions || function f(){echo hello world} || f() { echo hello world ; } || "function" is not defined by posix, only "name ()" is || || numeric C-like for loop || for ((i=0; i<3; i++)); do echo $i ; done || i=0 ; while test $i -lt 3 ; do echo $i ; i=$(($i+1)) ; done || the C-like for syntax (for (( ; ; ));do ..) is not defined by posix || || case || ;;& || || ;;& in bash4 is not defined by posix || || case || ;& || || ;& in bash4 is not defined by posix || || select || select || || select is not defined by posix || || expand sequences || echo $'hello\tworld' || printf "hello\tworld" || $' ' is not defined by posix || || extended glob || ( +() @( ) etc... || || not defined by posix || |
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| == Parameter Expansion | == Expansions == |
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| list of expansion not defined by posix: | * Brace Expansion, eg {1..10} is not defined by posix * <( ) >( ) process substitution is not defined by posix |
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| * ${name:n:l} * ${name/ } * ${!name} |
== Parameter Expansions == |
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| == Arrays | List of expansions not defined by posix: |
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| * arrays are not defined by posix. | * ${name:n:l} * ${name/ } * ${!name} |
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| == test | == Arrays == |
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| * [[ is not defined by posix * == as an argument of test (aka [) is not defined by posix * < > to compare numbers as argument of test is not defined by posix, though dash implements it * -nt, -ot, -ef are not defined by posix |
* arrays are not defined by posix. == Conditionals == |
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| == Builtins | * [[ is not defined by posix * == as an argument of test (aka [) is not defined by posix * < > to compare numbers as argument of test are not defined by posix, though dash implements them * -nt, -ot, -ef are not defined by posix * (( )) is not defined by posix |
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| * echo. posix doesn't define any options, use printf * printf "-v" is not defined by posix. also the %b and %q format are not defined by posix * read, the only option defined by posix is "-r" |
== Arithmetic == * ++ -- are not defined by posix == Redirections == * >& and &> are not defined by posix * m>n- m<n- ie duplicating and closing a descriptor at the same time is not defined by posix * |& (bash4) is not defined by posix == Builtins == * echo. posix doesn't define any options, use printf * printf "-v" is not defined by posix. also the %b and %q format are not defined by posix * read, the only option defined by posix is "-r" * shopt, and therefore all the options it provide, extglob, nullglob, dot glob etc ..are not defined by posix == more == * [[ http://www.gnu.org/software/bash/manual/html_node/Bash-POSIX-Mode.html#Bash-POSIX-Mode | The bash manual]] has a list of the difference between bash running in posix mode and a normal bash. Note that bash in posix mode is only guaranteed to run a shell written according to the posix specification. It doesn't mean that it will fail if you use bashisms in your scripts. |
How to make bash scripts work in dash
This page is an attempt to list some of the most common bashisms ie features not defined by POSIX (ie don't work in dash). It probably won't be exhaustive. Note also we talk about "bashism" because this wiki is largely bash centric but a number of these extensions work in other shells like ksh or zsh.
Syntax
|
Works in bash |
Change to for dash |
Comment |
defining functions |
function f(){echo hello world} |
f() { echo hello world ; } |
"function" is not defined by posix, only "name ()" is |
numeric C-like for loop |
for ((i=0; i<3; i++)); do echo $i ; done |
i=0 ; while test $i -lt 3 ; do echo $i ; i=$(($i+1)) ; done |
the C-like for syntax (for (( ; ; ));do ..) is not defined by posix |
case |
;;& |
|
;;& in bash4 is not defined by posix |
case |
;& |
|
;& in bash4 is not defined by posix |
select |
select |
|
select is not defined by posix |
expand sequences |
echo $'hello\tworld' |
printf "hello\tworld" |
$' ' is not defined by posix |
extended glob |
( +() @( ) etc... |
|
not defined by posix |
Expansions
- Brace Expansion, eg {1..10} is not defined by posix
<( ) >( ) process substitution is not defined by posix
Parameter Expansions
List of expansions not defined by posix:
- ${name:n:l}
- ${name/ }
- ${!name}
Arrays
- arrays are not defined by posix.
Conditionals
- [[ is not defined by posix
- == as an argument of test (aka [) is not defined by posix
< > to compare numbers as argument of test are not defined by posix, though dash implements them
- -nt, -ot, -ef are not defined by posix
- (( )) is not defined by posix
Arithmetic
- ++ -- are not defined by posix
Redirections
>& and &> are not defined by posix
m>n- m<n- ie duplicating and closing a descriptor at the same time is not defined by posix
|& (bash4) is not defined by posix
Builtins
- echo. posix doesn't define any options, use printf
- printf "-v" is not defined by posix. also the %b and %q format are not defined by posix
- read, the only option defined by posix is "-r"
- shopt, and therefore all the options it provide, extglob, nullglob, dot glob etc ..are not defined by posix
more
The bash manual has a list of the difference between bash running in posix mode and a normal bash.
Note that bash in posix mode is only guaranteed to run a shell written according to the posix specification. It doesn't mean that it will fail if you use bashisms in your scripts.