In a simple for loop, I'm trying to get it to increment which variable it echos. The unrolled version at the bottom works and does what I want, but how can I get the loop to work the same way?

for x in 0 1 2 3 4 do echo -ne $FVAR$x ":: " echo $LVAR$x
done echo -ne $FVAR0 ":: " echo $LVAR0 echo -ne $FVAR1 ":: " echo $LVAR1 echo -ne $FVAR2 ":: " echo $LVAR2 echo -ne $FVAR3 ":: " echo $LVAR3 echo -ne $FVAR4 ":: " echo $LVAR4

2

1 Answer

From the bash manual:-

If the first character of parameter is an exclamation point (!), and parameter is not a nameref, it introduces a level of variable indirection. Bash uses the value of the variable formed from the rest of parameter as the name of the variable; this variable is then expanded and that value is used in the rest of the substitution, rather than the value of parameter itself. This is known as indirect expansion.

So you need to store the name of the variable you want to expand in a separate variable, eg:-

for x in 0 1 2 3 4
do fv=FVAR$x lv=LVAR$x echo ${!fv} ":: " ${!lv}
done

You could alternatively define fv and lv as of type nameref: the code would be similar, except that there is no need for ! to expand the variables:-

declare -n fv
declare -n lv
for x in 0 1 2 3 4
do fv=FVAR$x lv=LVAR$x echo $fv ":: " $lv
done

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