associative array assignment from the output of a function
Hello
I try to assign an array from the output of a function. As this works
for indexed arrays, it does not for associative arrays. I m using "GNU
bash, version 4.1.7(1)-release (x86_64-redhat-linux-gnu)" on a Fedora 13
system.
An easy example is better than an explanation:
# Woks well
indexarray()
{
echo "5 6 7"
}
declare -a t1=( $(indexarray) )
echo ${t1[1]} ${t1[0]}
# Does not work
assocarray()
{
echo "[a]=5 [b]=6"
}
declare -A t1=( $(assocarray) ) # The error occurs here
The given error message is "cannot convert indexed to associative
array". Is this behaviour intended ? Is there a known workaround for this ?
I didnt find any "users" maling-list and I m not really sure this one
fit to my message, since this may (or may not) be a bug report.
Thanks for your answers, regards.
Re: associative array assignment from the output of a function
Le 22/10/2010 14:42, Greg Wooledge a écrit :
Unreliable at best. How do you handle elements that have whitespace
in them, for example? You have to know your data set, choose a delimiter
that can't be in that set, and then write code to parse the output stream
into elements.
At this moment, I "solve" the problem of whitespace with a custom IFS :
func()
{
echo "value 1\x1Evalue2"
}
IFS=$'\x1E' myvar=( $(func) )
Ick. You're attempting to use the language's internal assignment syntax
in *data*. Sounds like you're on the road to eval, and we all know
where *that* one ends!
What you appear to be attempting to do is "return an associative array
from a function to the caller". Bash's functions aren't really
*functions* in the mathematical sense, or even in the sense of most
high-level computing languages. They are really commands. User-definable
commands. They don't return data. They only return an exit status.
But that's a tangent. Anyway, if you want to make it so that after the
function has returned, the caller has a brand new associative array, then
what you need to do is:
1) Pre-declare the associative array in the CALLER, not in the function,
because it is currently not possible for a function to create an
associative array in the global namespace. AAs have to be created
by using "declare", and if you use "declare" inside a function, it
makes a local variable. Chet has said there will be a workaround
for this in bash 4.2.
2) Inside the function, put the data into the AA. No, you can't pass the
name of the array from the caller to the function either. You must
HARD-CODE the array's name in the function.
3) Make sure you do NOT call the function in a subshell.
Any attempts to return advanced data structures from a function using
the techniques you'd expect in a high-level language just won't work
in bash. It's a shell. It's not designed for this kind of task. Just
use a global variable and be happy.
Even if such needs of complex values built by functions are somewhat
unusual (or even just a bad idea), I came to the same conclusion to use
a global variable. Thanks a lot for your answer, I ll be happy with a
global variable.
Anyway, since this syntax works for assigning indexed arrays (even if
it's a "hack"), should it works for associative array assignment ?
Maintainers will decide I assume.
Re: associative array assignment from the output of a function
Le 22/10/2010 14:56, Chet Ramey a écrit :
And you're trying to redeclare it as an associative array here. The
variable already exists; you can't convert it between array types;
and bash tells you this. If you want an associative array, unset the
variable before you declare it.
After your answer, I checked and I think the error message is not
related to the variable name collision :
[a...@axel-asus plugins]$ unset foo
[a...@axel-asus plugins]$ func()
> {
> echo "[a]=5 [b]=10"
> }
[a...@axel-asus plugins]$ declare -A foo=( $(func) )
-bash: foo: [a]=5: must use subscript when assigning associative array
-bash: foo: [b]=10: must use subscript when assigning associative array
[a...@axel-asus plugins]$ echo ${foo[a]}
[a...@axel-asus plugins]$ declare -a bar=( $(func) )
[a...@axel-asus plugins]$ echo ${bar[0]}
[a]=5
Re: associative array assignment from the output of a function
Le 22/10/2010 16:21, Greg Wooledge a écrit :
On Fri, Oct 22, 2010 at 02:59:37PM +0200, Axel wrote:
Anyway, since this syntax works for assigning indexed arrays (even if
it's a "hack"), should it works for associative array assignment ?
Maintainers will decide I assume.
But it doesn't. You used a totally different syntax for your indexed
array example. If you had used the same syntax, it would have looked
like this:
imadev:~$ unset array
imadev:~$ f() { echo '[0]=alpha [2]=beta'; }; array=( $(f) )
imadev:~$ set | grep ^array=
array=([0]="[0]=alpha" [1]="[2]=beta")
It doesn't "work" in the indexed array case either.
Ok I see what you mean, finally it works only for indexed arrays without
explicit indexes. I understand that point.
There's another hazard you haven't taken into account (although it's
only a hazard when dealing with general strings; numbers are safe).
The unquoted substitution $(f) is subject to both word-splitting (which
you've been taking advantage of) *and* globbing.
imadev:~$ f() { echo '+ - * /'; }; array=( $(f) )
imadev:~$ echo "${array[42]}"
baz
imadev:~$ echo "${array[54]}"
blah.txt
imadev:~$ echo ${#arr...@]}
901
If you're going to use array=( $... ) with arbitrary strings being
possible in the substitution, then you should disable globbing first
(with set -f) to avoid potential disasters.
Thanks again for those advices.
Regards
weird insert of backslashes in strings
Configuration Information [Automatically generated, do not change]:
Machine: i686
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -fstack-protector -Wno-parentheses -Wno-format-security
uname output: Linux bongo 2.6.32-042stab134.8 #1 SMP Fri Dec 7 17:16:09 MSK
2018 i686 i686 i386 GNU/Linux
Machine Type: i686-pc-linux-gnu
Bash Version: 5.0
Patch Level: 0
Release Status: release
Description:
This script "weirdbackslashes":
$ cat weirdbackslashes
#===begin
PRE='\/'
echo 'define'${PRE}'\
/'
#===end
produces with bash4:
$ bash weirdbackslashes
define\/\
/
and with bash5:
$ bash5 weirdbackslashes
\d\e\f\i\n\e\/\\\
/
Repeat-By:
see Description
bash --login in Cygwin environment does not use %HOME% when doing tilde expansion.
Configuration Information [Automatically generated, do not change]: Machine: i686 OS: cygwin Compiler: i686-pc-cygwin-gcc Compilation CFLAGS: -DPROGRAM='bash.exe' -DCONF_HOSTTYPE='i686' -DCONF_OSTYPE='cygwin' -DCONF_MACHTYPE='i688 6-pc-cygwin' -DCONF_VENDOR='pc' -DSHELL -DHAVE_CONFIG_H -DRECYCLES_PIDS -I. -I/home/RLandheer/cygwin-contrr ib/bash/2.05b-16/bash-2.05b -I/home/RLandheer/cygwin-contrib/bash/2.05b-16/bash-2.05b/include -I/home/RLandhh eer/cygwin-contrib/bash/2.05b-16/bash-2.05b/lib -O2 uname output: CYGWIN_NT-5.0 WORK-ABB 1.5.10(0.116/4/2) 2004-05-25 22:07 i686 unknown unknown Cygwin Machine Type: i686-pc-cygwin Bash Version: 2.05b Patch Level: 0 Release Status: release Description: When invoking bash on a Windows machine with the --login option, tilde expansion is not done using the %HOME% environment variable. Repeat-By: Set HOME in the ControlPanel>System>Advanced>EnvironmentVariables>User variables for abb Invoke bash by calling bash.bat containing: @echo off c: chdir C:\bin\cygwin\bin bash --login -i Axel B. Bregnsbo ASIC Designer, M.Sc.EE +45 44855990 [EMAIL PROTECTED] -- entropy is time symmetric ___ Bug-bash mailing list Bug-bash@gnu.org http://lists.gnu.org/mailman/listinfo/bug-bash
