Shell script: while variable concatenation

This is my straightforward function:

generate_post_data()
{
cat <<-EOF
{"stringData": {}}
EOF
}


This is my other function:

generate_curl_body()
{
template=$(generate_post_data $secret_id)
echo "$template"
echo "$KVS_VARIABLES" | while read -r key value
do
template=$(echo "$template" | jq ".stringData += { "$key" : "$value" }")
echo $template
done
}


The output is:

#Before while -> {"stringData": {}}
#1 iteration -> { "stringData": { "VAR1": "VAL1" } }
#2 iteration -> { "stringData": { "VAR1": "VAL1", "VAR2": "VAL2" } }
#3 iteration -> { "stringData": { "VAR1": "VAL1", "VAR2": "VAL2", "VAR3": "VAL3" } }
#After while -> {"stringData": {}}


Why template variable is not filled?

template

1 Answer
1

It is not filled because the | while is executed in subshell. From the manual page of Bash (for example):

| while

Each command in a pipeline is executed as a separate process (i.e., in a subshell).

If the shell is Bash, the easy fix is to replace the echo "$KVS_VARIABLES" | with a here-string:

echo "$KVS_VARIABLES" |

while read -r key value; do
template=$(echo "$template" | jq ".stringData += { "$key" : "$value" }")
echo $template
done <<< "$KVS_VARIABLES"


If your shell does not accept here-strings, you can always wrap the while in a compound command { while ... done; echo "$template"; } and use an extra command substitution:

while

{ while ... done; echo "$template"; }

template="$(
echo "$KVS_VARIABLES" |
{
while read -r key value; do
template=$(
echo "$template" |
jq ".stringData += { "$key" : "$value" }"
)
done
echo "$template"
}
)"


!/usr/bin/env sh

Syntax error: redirection unexpected

/bin/sh

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