CODEWITHSUNDEEP
shellunix
Babbi
Babbi

Reputation: 65

making variable with the values of another variable in unix shell scripting

I need to make variable using two other variable values.

#i have two variable in unix i.e.#
v_a=a
v_b=b
##now i want to combine the two values of the two variable and the result of that i want that as a variable means v_a_b and use it.##
echo 'v_'$v_a'_'$v_b #the output will be v_a_b and i want to use it like $v_a_b

Upvotes: 0

Views: 327

Answers (4)

Babbi
Babbi

Reputation: 65

   v_a=a
   v_b=b
   v_a_b=c
   eval V_XYZ='$'"v_"$v_a"_"$v_b
   echo 'Value= '$V_XYZ

output will be c

Upvotes: 0

Walter A
Walter A

Reputation: 19982

Suppose you have the following vars:

v_a=a
v_b=b
v_a_b="I want this one"
v_a_c="Wrong one!"

How do you get I want this one using the values of v_a and v_b ?
You can use eval, but try to avoid that:

# don't do this
eval echo "\$v_${v_a}_${v_b}"

You need a new variable , lets call it c and get the value of the constructed var:

c="v_${v_a}_${v_b}"
echo "Using the exclamation mark for retrieving the valueCombined: ${!c}"

Another way is using printf:

printf -v c "v_%s_%s" "${v_a}"  "${v_b}"
echo "Combined: ${!c}"

Upvotes: 3

James Marble
James Marble

Reputation: 883

If I understand correctly, you want to concatenate the contents of variables v_a and v_b (along with some fixed strings 'v_' and '_') then store it in a variable named v_a_b.

v_a=a
v_b=b
v_a_b='v_'$a'_'$b
echo $v_a_b

The output is v_a_b.

Upvotes: 0

pdg
pdg

Reputation: 103

Use eval to explicitly pre-evaluate an expression.
for your question,

eval 'echo \$v_"$v_a"_"$v_b"'

should work fine,
echo \$v_"$v_a"_"$v_b" evaluates to echo $v_a_b, then the intermediate result is evaluated again, so in effect, we get the result of $(echo $v_a_b) note: you might want to quote the variable $v_a_b:

eval 'echo \"\$v_"$v_a"_"$v_b"\"'

Upvotes: 0

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