Use of associative array with a variable name under bash 4.1 - bash

Question

I trying to parse multiples files like this under bash-4.1
$cat hostname_abc.txt
host_type type_foo
SoftA version123
SoftB version456
to obtain an output where you can see how many times a version of Soft[A,B] is used, grouped by host type :
$./list_versions.sh
[type_foo] 11 times
SoftA:
[version123] 1 times
[version444] 5 times
[version567] 5 times
SoftB:
[version456] 9 times
[version777] 2 times
[type_bar] 6 times
SoftA:
[version444] 6 times
SoftB:
[version111] 4 times
[version777] 2 times
I don't know in advance the list of host_type and the versions.
So I tried to save in an associative array the count of each host_type and create dynamically the names of the associatives arrays which stored the count of each version of Soft[A,B] per host_type based base on a template host_type_Soft[A,B]
I tried many times with different variations of syntax and indirections so I remade below a more readable script that follow my aim :
#!/usr/bin/env bash
# ----- generated test conditions -----
echo -e "host_type typeA\nSoftA v2\nSoftB v1" > hostname_1.txt
echo -e "host_type typeB\nSoftA v1\nSoftB v1" > hostname_2.txt
echo -e "host_type typeB\nSoftA v1\nSoftB v0" > hostname_3.txt
echo -e "host_type typeA\nSoftA v0\nSoftB v0" > hostname_4.txt
echo -e "host_type typeA\nSoftA v3\nSoftB v2" > hostname_5.txt
echo -e "host_type typeB\nSoftA v3\nSoftB v1" > hostname_6.txt
echo -e "host_type typeB\nSoftA v2\nSoftB v2" > hostname_7.txt
echo -e "host_type typeA\nSoftA v1\nSoftB v2" > hostname_8.txt
echo -e "host_type typeC\nSoftA v0\nSoftB v4" > hostname_9.txt
list_hostname() {
for i in {1..9}; do
echo "hostname_${i}.txt"
done
}
declare -A list_host_type
while read f; do
#parse the hostname files
while read l; do
[[ $l = *"host_type"* ]] && host_type="$( echo $l | cut -d' ' -f2)"
[[ $l = *"SoftA"* ]] && versionA="$( echo $l | cut -d' ' -f2)"
[[ $l = *"SoftB"* ]] && versionB="$( echo $l | cut -d' ' -f2)"
done < <( cat "$f" )
#count the number of hosts by host_type
[[ ${list_host_type[$host_type]} ]] && ((list_host_type[$host_type]++)) || list_host_type[$host_type]='1'
#create associative arrays with a name only know at runtime
declare -A "${host_type}_SoftA"
declare -A "${host_type}_SoftB"
#count the number of host for the couple host_type and Soft[A,B], stored on the dynamically named assiociative array
[[ ${${host_type}_SoftA[$versionA]} ]] && ((${host_type}_SoftA[$versionA]++)) || ${host_type}_SoftA[$versionA]='1'
[[ ${${host_type}_SoftB[$versionB]} ]] && ((${host_type}_SoftB[$versionB]++)) || ${host_type}_SoftB[$versionB]='1'
done < <( list_hostname )
#print a non pretty-formated output
echo '==== result ====='
for m in "${!list_host_type[#]}"; do
echo "host type: $m count: ${list_model[$m]}"
for versionA in "${!${m}_softA[#]}"; do
echo " SoftA version: $versionA count: ${${m}_SoftA[$versionA]}"
done
for versionB in "${!${m}_softB[#]}"; do
echo " SoftB version: $versionB count: ${${m}_SoftB[$versionB]}"
done
done
I know they are others methods to achieve my goal but I want to know if I can use associative this way with bash-4.1.

Answer 1

I don't think you can use dynamic variable names with arrays in Bash.
(I tried a few things but couldn't figure out the syntax.)
Even if possible, I think it would be extremely difficult to understand.
A possible workaround could be using a single associative array,
with "composite keys".
That is, for example use a comma separated value of host type, soft and version:
while read f; do
line=0
while read col1 col2; do
if [[ $line = 0 ]]; then
host_type=$col2
else
soft=$col1
version=$col2
index=$host_type,$soft,$version
((list_host_type[$index]++))
fi
((line++))
done < <( cat "$f" )
done < <( list_hostname )
for m in "${!list_host_type[#]}"; do
echo $m = ${list_host_type[$m]}
done
For your sample data this would produce:
typeA,SoftA,v2 = 1
typeA,SoftA,v3 = 1
typeA,SoftA,v0 = 1
typeA,SoftA,v1 = 1
typeB,SoftA,v3 = 1
typeB,SoftA,v2 = 1
typeB,SoftA,v1 = 2
typeA,SoftB,v2 = 2
typeA,SoftB,v1 = 1
typeA,SoftB,v0 = 1
typeC,SoftB,v4 = 1
typeB,SoftB,v2 = 1
typeB,SoftB,v0 = 1
typeB,SoftB,v1 = 2
typeC,SoftA,v0 = 1
And then work with this associative array to compute the statistics you need. Here's a rough example implementation:
get_host_types() {
local names=(${!list_host_type[#]})
printf "%s\n" "${names[#]%%,*}" | sort -u
}
get_soft() {
local host_type=$1
local names=(${!list_host_type[#]})
for name in "${names[#]}"; do
[[ ${name%%,*} = $host_type ]] && echo $name
done | cut -d, -f2 | sort -u
}
get_versions() {
local prefix=$1
local names=(${!list_host_type[#]})
for name in "${names[#]}"; do
[[ ${name%,*} = $prefix ]] && echo $name
done | cut -d, -f3 | sort -u
}
indent=" "
for host_type in $(get_host_types); do
echo "[$host_type]"
for soft in $(get_soft $host_type); do
echo "$indent$soft:"
for version in $(get_versions $host_type,$soft); do
index=$host_type,$soft,$version
echo "$indent$indent[$version] ${list_host_type[$index]} times"
done
done
done
Producing as output:
[typeA]
SoftA:
[v0] 1 times
[v1] 1 times
[v2] 1 times
[v3] 1 times
SoftB:
[v0] 1 times
[v1] 1 times
[v2] 2 times
[typeB]
SoftA:
[v1] 2 times
[v2] 1 times
[v3] 1 times
SoftB:
[v0] 1 times
[v1] 2 times
[v2] 1 times
[typeC]
SoftA:
[v0] 1 times
SoftB:
[v4] 1 times
All in all, it would be better to implement this using a proper programming language.