CODEWITHSUNDEEP
linuxbashshellvariablesunix
Stack Learner
Stack Learner

Reputation: 129

Declaring variables with indirect reference with a prefix

I have my parameters stored in a file and calling them with a prefix which i get it has input. now, i am getting the input and prefixing it and storing as a new variable and then pointing my new variable indirectly to my actual variable to use in my script.

Is there a way to directly mention the indirect variable pointer to my main variable like value1=$(!$pk_value1) something like this, so that i can skip the new variable declaration. i have close to 10 variables to be declared which makes my code lengthy.

My current code : 

source values.sh
read -p "Enter Identifier : " pk

value1here=${pk}_value1
value2here=${pk}_value2
value3here=${pk}_value3

value1=${!value1here}
value2=${!value2here}
value3=${!value3here}

values.sh (I have close to 300 variables declared here)

p1_value1=name1
p1_value2=host1
p1_value3=user1

p2_value1=name2
p2_value2=host2
p2_value3=user2

Is there a way to directly mention the indirect variable pointer + my name like value1=$(!$pk_value1) something like this, so that i can skip the new variable declaration. i have close to 10 variables to be declared which makes my code lengthy.

Upvotes: 1

Views: 191

Answers (1)

Léa Gris
Léa Gris

Reputation: 19655

If your Bash is recent enough, then use the -n indirect variable attribute like this:

#!/usr/bin/env bash

source values.sh
read -r -p 'Enter Identifier : ' pk

declare -n \
  value1="${pk}_value1" \
  value2="${pk}_value2" \
  value3="${pk}_value3"

Alternate method with populating an associative array from the file values.sh:

#!/usr/bin/env bash

declare -A values="($(
  xargs -l1 \
    bash -c \
    'IFS="=" read -r k v <<<"$@"; printf "[%q]=%q\n" "$k" "$v"' _ \
    <values.sh
))"

read -r -p 'Enter Identifier : ' pk

declare -- \
  value1="${values[${pk}_value1]}" \
  value2="${values[${pk}_value2]}" \
  value3="${values[${pk}_value3]}"

Working of the Associative array population:

xargs -l1 will translate the stdio input stream's lines (here: <values.sh) into arguments to a command.

The command called by xargs is bash -c, witch executes an inline script detailed here:

# Read variables k and v from the arguments
# streamed as a here-string <<<"",
# using the = sign as the Internal Field Separator.
# Actually splitting key=value into k and v.
IFS="=" read -r k v <<<"$@"

# Format variables k and v into an Associative array
# entry declaration in the form [key]=value,
# with %q adding quotes or escaping if required.
printf "[%q]=%q\n" "$k" "$v"

Finally the Associative array declaration and assignment declare -A values="($(commands))" gets the entries generated by the xarg and inline shell script commands.

Upvotes: 4

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