${!variable@operator} does not work for variables without values.
See empty values for all occurrences of ${!var@...} below.
${variable@A} does not work for scalar variables without values, but
interestingly ${variable[@]@A} works for them.
See difference between ${VAR1@A} and ${VAR1[@]@A} below.
However neither ${variable@A} nor ${variable[@]@A} works for arrays
without values.
Both ${variable@a} and ${variable[@]@a} work for scalar variables
without values.
However ${variable[@]@a} does not work for arrays without values.
See difference between ${VAR3@a} and ${VAR3[@]@a}, and between
${VAR5@a} and ${VAR5[@]@a} below.
(BASH 5.0.16.)
$ declare -lr VAR1
$ declare -lr VAR2=zzz
$ declare -alr VAR3
$ declare -alr VAR4=(zzz)
$ declare -Alr VAR5
$ declare -Alr VAR6=([0]=zzz)
$ declare -p VAR{1,2,3,4,5,6}
declare -rl VAR1
declare -rl VAR2="zzz"
declare -arl VAR3
declare -arl VAR4=([0]="zzz")
declare -Arl VAR5
declare -Arl VAR6=([0]="zzz" )
$ for operator in Q E P A a ; do for var in VAR{1,2,3,4,5,6} ; do echo
"var=${var}" ; eval "echo \"\\\${!var@${operator}}:
'\${!${var}@${operator}}'\"" ; eval "echo \"\\\${!var[@]@${operator}}:
'\${!${var}[@]@${operator}}'\"" ; eval "echo
\"\\\${${var}@${operator}}: '\${${var}@${operator}}'\"" ; eval
"echo \"\\\${${var}[@]@${operator}}: '\${${var}[@]@${operator}}'\"" ;
echo ; done ; done
var=VAR1
${!var@Q}: ''
${!var[@]@Q}: ''
${VAR1@Q}: ''
${VAR1[@]@Q}: ''
var=VAR2
${!var@Q}: ''
${!var[@]@Q}: ''
${VAR2@Q}: ''zzz''
${VAR2[@]@Q}: ''zzz''
var=VAR3
${!var@Q}: ''
${!var[@]@Q}: ''
${VAR3@Q}: ''
${VAR3[@]@Q}: ''
var=VAR4
${!var@Q}: ''
${!var[@]@Q}: ''
${VAR4@Q}: ''zzz''
${VAR4[@]@Q}: ''zzz''
var=VAR5
${!var@Q}: ''
${!var[@]@Q}: ''
${VAR5@Q}: ''
${VAR5[@]@Q}: ''
var=VAR6
${!var@Q}: ''
${!var[@]@Q}: ''
${VAR6@Q}: ''zzz''
${VAR6[@]@Q}: ''zzz''
var=VAR1
${!var@E}: ''
${!var[@]@E}: ''
${VAR1@E}: ''
${VAR1[@]@E}: ''
var=VAR2
${!var@E}: ''
${!var[@]@E}: ''
${VAR2@E}: 'zzz'
${VAR2[@]@E}: 'zzz'
var=VAR3
${!var@E}: ''
${!var[@]@E}: ''
${VAR3@E}: ''
${VAR3[@]@E}: ''
var=VAR4
${!var@E}: ''
${!var[@]@E}: ''
${VAR4@E}: 'zzz'
${VAR4[@]@E}: 'zzz'
var=VAR5
${!var@E}: ''
${!var[@]@E}: ''
${VAR5@E}: ''
${VAR5[@]@E}: ''
var=VAR6
${!var@E}: ''
${!var[@]@E}: ''
${VAR6@E}: 'zzz'
${VAR6[@]@E}: 'zzz'
var=VAR1
${!var@P}: ''
${!var[@]@P}: ''
${VAR1@P}: ''
${VAR1[@]@P}: ''
var=VAR2
${!var@P}: ''
${!var[@]@P}: ''
${VAR2@P}: 'zzz'
${VAR2[@]@P}: 'zzz'
var=VAR3
${!var@P}: ''
${!var[@]@P}: ''
${VAR3@P}: ''
${VAR3[@]@P}: ''
var=VAR4
${!var@P}: ''
${!var[@]@P}: ''
${VAR4@P}: 'zzz'
${VAR4[@]@P}: 'zzz'
var=VAR5
${!var@P}: ''
${!var[@]@P}: ''
${VAR5@P}: ''
${VAR5[@]@P}: ''
var=VAR6
${!var@P}: ''
${!var[@]@P}: ''
${VAR6@P}: 'zzz'
${VAR6[@]@P}: 'zzz'
var=VAR1
${!var@A}: ''
${!var[@]@A}: ''
${VAR1@A}: ''
${VAR1[@]@A}: 'declare -rl VAR1='''
var=VAR2
${!var@A}: ''
${!var[@]@A}: ''
${VAR2@A}: 'declare -rl VAR2='zzz''
${VAR2[@]@A}: 'declare -rl VAR2='zzz''
var=VAR3
${!var@A}: ''
${!var[@]@A}: ''
${VAR3@A}: ''
${VAR3[@]@A}: ''
var=VAR4
${!var@A}: ''
${!var[@]@A}: ''
${VAR4@A}: 'declare -arl VAR4='zzz''
${VAR4[@]@A}: 'declare -arl VAR4=([0]="zzz")'
var=VAR5
${!var@A}: ''
${!var[@]@A}: ''
${VAR5@A}: ''
${VAR5[@]@A}: ''
var=VAR6
${!var@A}: ''
${!var[@]@A}: ''
${VAR6@A}: 'declare -Arl VAR6='zzz''
${VAR6[@]@A}: 'declare -Arl VAR6=([0]="zzz" )'
var=VAR1
${!var@a}: ''
${!var[@]@a}: ''
${VAR1@a}: 'rl'
${VAR1[@]@a}: 'rl'
var=VAR2
${!var@a}: ''
${!var[@]@a}: ''
${VAR2@a}: 'rl'
${VAR2[@]@a}: 'rl'
var=VAR3
${!var@a}: ''
${!var[@]@a}: ''
${VAR3@a}: 'arl'
${VAR3[@]@a}: ''
var=VAR4
${!var@a}: ''
${!var[@]@a}: ''
${VAR4@a}: 'arl'
${VAR4[@]@a}: 'arl'
var=VAR5
${!var@a}: ''
${!var[@]@a}: ''
${VAR5@a}: 'Arl'
${VAR5[@]@a}: ''
var=VAR6
${!var@a}: ''
${!var[@]@a}: ''
${VAR6@a}: 'Arl'
${VAR6[@]@a}: 'Arl'
$
--
Arfrever Frehtes Taifersar Arahesis
