Bash unbound variable array (script: s3-bash)

Question

I am working with: s3-bash, when I run it in my local environment (OS X 10.10.1) I don't have any problems, when I try to run it on a ubuntu server 14.04.1 I get the following error:

./s3-common-functions: line 66: temporaryFiles: unbound variable
./s3-common-functions: line 85: temporaryFiles: unbound variable

I've looked at the s3-common-functions script and the variable looks to be initialized properly (as an array):

# Globals
declare -a temporaryFiles

But there is a note in the comment, and I'm sure if it's related:

# Do not use this from directly. Due to a bug in bash, array assignments do not work when the function is used with command substitution
function createTemporaryFile
{
    local temporaryFile="$(mktemp "$temporaryDirectory/$$.$1.XXXXXXXX")" || printErrorHelpAndExit "Environment Error: Could not create a temporary file. Please check you /tmp folder permissions allow files and folders to be created and disc space." $invalidEnvironmentExitCode
    local length="${#temporaryFiles[@]}"
    temporaryFiles[$length]="$temporaryFile"
}

unbound variable is what you get when using set -u. Do you have that set in whatever environment you are running the script? — Etan Reisner
– Etan Reisner, Commented Jan 20, 2015 at 21:23
Bug? What's described in the comment text is not a bug, but normal and expected behavior. foo=$(bar) runs bar in a subshell, so of course assignments done inside that subshell don't propagate to the parent shell. — Charles Duffy
– Charles Duffy, Commented Jan 20, 2015 at 22:19
(I wonder how old of a bash interpreter s3-bash tries to support; that particular method for appending to an array hasn't been necessary for rather a while, the new syntax being temporaryFiles+=( "$temporaryFile" )... though, of course, that doesn't change anything about propagation of variables from subshells to parents). — Charles Duffy
– Charles Duffy, Commented Jan 20, 2015 at 22:21
@EtanReisner looking at the source set -u is called a few lines above as well as set -e, I'm not an expert in bash so I'm not sure the effect, but I shouldn't have to set any env. variables to run the script (I don't believe). It also appears to fail when reading the array length local length="${#temporaryFiles[@]}" & length="${#temporaryFiles[@]}" — jordan.baucke
– jordan.baucke, Commented Jan 21, 2015 at 1:35

Etan Reisner · Accepted Answer · 2015-03-18 22:58:29Z

12

There appears to be a bash behaviour change at play here.

Found by kojiro: CHANGES

hhhh. Fixed a bug that caused `declare' and `test' to find variables that had been given attributes but not assigned values. Such variables are not set.

$ bash --version
GNU bash, version 3.2.25(1)-release (x86_64-redhat-linux-gnu)
Copyright (C) 2005 Free Software Foundation, Inc.
$ set -u
$ declare -a tF
$ echo "${#tF[@]}"
0

vs.

$ bash --version
GNU bash, version 4.1.2(1)-release (x86_64-redhat-linux-gnu)
Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
$ set -u
$ declare -a tF
$ echo "${#tF[@]}"
0

vs.

$ bash --version
GNU bash, version 4.3.30(1)-release (x86_64-pc-linux-gnu)
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>

This is free software; you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
$ set -u
$ declare -a tF
$ echo "${#tF[@]}"
-bash: tF: unbound variable

You can use declare -a tF=() on the newer bash versions to work around this.

$ declare -a tF=()
$ echo "${#tF[@]}"
0

edited Mar 18, 2015 at 22:58

answered Jan 21, 2015 at 2:43

Etan Reisner

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3 Comments

kojiro Over a year ago

Changed between bash-4.2-release and bash-4.3-alpha: hhhh. Fixed a bug that caused `declare' and `test' to find variables that had been given attributes but not assigned values. Such variables are not set. – (sorry txt doesn't allow more precise linking, but you can search for the exact text if you like.)

Etan Reisner Over a year ago

@kojiro Thanks for finding that.

U. Windl Over a year ago

In BASH 4.3 (bash-4.3-83.33.1.x86_64 of SLES 12 SP5 declare -a a=() still(?) causes an unbound variable for "${a[@]}".

U. Windl · Accepted Answer · 2022-11-11 14:43:13Z

5

Bash can substitute an empty value into unset variables using a dash.

set -u
my_array=()
printf "${my_array[@]-}\n"

This specific example will print nothing, but it will not give you an unbound variable error either.

Stolen from Bash: Error `Unbound variable' when appending to empty array ¹.

However, when used for a loop, you get one iteration (not zero) then:

for i in "${my_array[@]-}"
do
    echo $i
done

Expectation might be to get zero iterations.

It could be fixed this way then:

[ ${#my_array[@]} -gt 0 ] &&
for i in "${my_array[@]}"
do
    echo $i
done

edited Nov 11, 2022 at 14:43

U. Windl

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answered Jun 3, 2015 at 18:58

kurczynski

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2 Comments

kenj Over a year ago

That will not work when trying to find the size. I.e. ${#my_array[@]-} will generate a bad substitution error.

Davor Cubranic Over a year ago

This solved it for me, since my Centos 7.7 host is running Bash 4.2.46(2), which otherwise has an error if I try to iterate over an empty array.

jordan.baucke · Accepted Answer · 2015-01-21 02:05:01Z

0

Changed declaration of array for temporaryfiles

declare -a temporaryFiles

to:

temporaryFiles=()

Why this is different / non-function in ubuntu 14.04.1 Linux 3.13.0-32-generic x86_64 versus OS X I am not sure ?

answered Jan 21, 2015 at 2:05

jordan.baucke

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Comments

tractor boy · Accepted Answer · 2018-09-04 12:53:00Z

0

find $fullfolder -type f |
while read fullfile
do
    filename=$(basename "$fullfile")
    ext=$([[ $filename = *.* ]] && printf %s ${filename##*.} || printf 'NONE')
    arr+=($ext)
    echo ${#arr[@]}
done
echo ${#arr[@]}

Why does the ${#arr[@]} inside the for loop produce the correct result but the one outside gives 0?

answered Sep 4, 2018 at 12:53

tractor boy

7711 bronze badges

1 Comment

U. Windl Over a year ago

You pipe! ("'Each command in a pipeline is executed as a separate process (i.e., in a subshell).*" And don't ask questions in answers! Maybe see unix.stackexchange.com/q/9954/320598 and similars...

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