Shell : create and assign variables inside for loop - linux

Question

i ve this shell script ; it's a loop which set in the variable "a" each time result :
declare -a names=("one" "two" "three" "four")
for item in "${names[#]}";
do
a="$(cat <<-EOF
{
"NAME": "${item}_ABC",
"CHANGED": "${item}_CHANGING",
"VERSION": "${item}_GC",
}
EOF
)"
done
echo $a
My Purpose is how to change "a" by a dynamic variable name which be $item_MYPREFIX
(concatination :$item + _MYPREFIX )
So that my code would be generic , something like this :
for item in "${names[#]}";
do
$item_MYPREFIX="$(cat <<-EOF
{
"NAME": "${item}_ABC",
"CHANGED": "${item}_CHANGING",
"VERSION": "${item}_GC",
}
EOF
)"
done
and i would be able to display each variable : echo $one_MYPREFIX , echo $two_MYPREFIX ....
Of course it's not alerady working
Suggestions , to crrect it ?

Answer 1

Use an associative array.
declare -A foo
for item in "${names[#]}";
do
foo[$item]="{
\"NAME\": \"${item}_ABC\",
\"CHANGED\": \"${item}_CHANGING\",
\"VERSION\": \"${item}_GC\"
}"
done

Answer 2

Try it like this
#!/bin/bash
for item in "${names[#]}"; do
varname=${item}_MYPREFIX
declare $varname="
{
\"NAME\": \"${item}_ABC\",
\"CHANGED\": \"${item}_CHANGING\",
\"VERSION\": \"${item}_GC\",
}
"
echo "${!varname}"
done
But better use arrays for that.
#!/bin/bash
declare -A array
names=("one" "two" "three" "four")
for item in "${names[#]}"; do
indexname=${item}_MYPREFIX
array[$indexname]="
{
\"NAME\": \"${item}_ABC\",
\"CHANGED\": \"${item}_CHANGING\",
\"VERSION\": \"${item}_GC\",
}
"
echo "${array[$indexname]}"
done

Answer 3

This is really not best practice, but you can (in bash) do:
$ cat a.sh
#!/bin/bash
declare -a names=("one" "two" "three" "four")
for item in "${names[#]}"; do
eval "read -d '' ${item}_MYPREFIX" << EOF
{
"NAME": "${item}_ABC",
"CHANGED": "${item}_CHANGING",
"VERSION": "${item}_GC",
}
EOF
done
for item in "${names[#]}"; do
k="${item}_MYPREFIX"
echo "$k = ${!k}"
done
$ ./a.sh
one_MYPREFIX = {
"NAME": "one_ABC",
"CHANGED": "one_CHANGING",
"VERSION": "one_GC",
}
two_MYPREFIX = {
"NAME": "two_ABC",
"CHANGED": "two_CHANGING",
"VERSION": "two_GC",
}
three_MYPREFIX = {
"NAME": "three_ABC",
"CHANGED": "three_CHANGING",
"VERSION": "three_GC",
}
four_MYPREFIX = {
"NAME": "four_ABC",
"CHANGED": "four_CHANGING",
"VERSION": "four_GC",
}
I believe the only bashism there (besides the existence of arrays, but several shells have arrays) is the usage of ${!...} indirection, but that's just for output and is not really necessary. However, since you're using a shell that supports arrays, you might as well not do this at all. Instead of creating a variable named "two_MYPREFIX", you ought to create an array and store that value in either index 2, or use an associative array and store in with index "two". That would be much cleaner than using eval.

Answer 4

The heredocs is not needed, try this.
#!/usr/bin/env bash
declare -a names=("one" "two" "three" "four")
declare -a prefix=(foo bar baz more)
for item in "${!names[#]}"; do
array+=("${prefix[$item]} = {
"NAME": "${names[$item]}_ABC",
"CHANGED": "${names[$item]}_CHANGING",
"VERSION": "${names[$item]}_GC",
}"
)
done
printf '%s\n' "${array[#]}"
Output
foo = {
NAME: one_ABC,
CHANGED: one_CHANGING,
VERSION: one_GC,
}
bar = {
NAME: two_ABC,
CHANGED: two_CHANGING,
VERSION: two_GC,
}
baz = {
NAME: three_ABC,
CHANGED: three_CHANGING,
VERSION: three_GC,
}
more = {
NAME: four_ABC,
CHANGED: four_CHANGING,
VERSION: four_GC,
}

Answer 5

Bash solution without eval, without associative array and using a template:
#!/usr/bin/env bash
declare -a names=("one" "two" "three" "four")
read -r -d '' template <<'EOF'
{
"NAME": "%q_ABC",
"CHANGED": "%q_CHANGING",
"VERSION": "%q_GC"
}
EOF
for item in "${names[#]}"; do
# shellcheck disable=SC2059 # format with a template variable
printf -v "${item}_MYPREFIX" "$template" "$item" "$item" "$item"
done
# Dump variables for debug
IFS=$'\n' read -r -d '' -a k < <(printf '%s_MYPREFIX\n' "${names[#]}")
typeset -p "${k[#]}"
Output:
declare -- one_MYPREFIX="{
\"NAME\": \"one_ABC\",
\"CHANGED\": \"one_CHANGING\",
\"VERSION\": \"one_GC\"
}"
declare -- two_MYPREFIX="{
\"NAME\": \"two_ABC\",
\"CHANGED\": \"two_CHANGING\",
\"VERSION\": \"two_GC\"
}"
declare -- three_MYPREFIX="{
\"NAME\": \"three_ABC\",
\"CHANGED\": \"three_CHANGING\",
\"VERSION\": \"three_GC\"
}"
declare -- four_MYPREFIX="{
\"NAME\": \"four_ABC\",
\"CHANGED\": \"four_CHANGING\",
\"VERSION\": \"four_GC\"
}"