in POSIX shell, how to print the value of the value of a variable

Question

In a POSIX shell:

>VALUE=value
>FOOBAR=VALUE

Now how to print the value of $FOOBAR? $$FOOBAR does not work - it goes left-to-right so interprets $$ first as process ID.

The duplicate question before me that people are pointing to, yes it does contain the answer to my question but it buried in a ton of irrelevant gunk. My question is much simpler and to the point.

@Bharel of course does not work, for the same reason as above - the shell interprets left to right — Mark Galeck, Mar 26 '16 at 13:05
http://stackoverflow.com/questions/10757380/bash-variable-variables — Karoly Horvath, Mar 26 '16 at 13:06
@KarolyHorvath yes there is the answer there in your link, use `eval`: `eval echo \$$FOOBAR` . Please make it an answer, I will accept. — Mark Galeck, Mar 26 '16 at 13:13
Possible duplicate of [Indirect parameter substitution in shell script](http://stackoverflow.com/questions/4380478/indirect-parameter-substitution-in-shell-script) — Gilles 'SO- stop being evil', Mar 26 '16 at 13:18

score 1 · Accepted Answer · answered Mar 26 '16 at 13:16

1

The only way to do this in POSIX is to use eval, so be very certain that FOOBAR contains nothing more than a valid variable name.

$ VALUE=value
$ FOOBAR=VALUE
$ valid_var='[[:alpha:]_][[:alnum:]_]*$'
$ expr "$FOOBAR" : "$valid_var" > /dev/null && eval "echo \$$FOOBAR"

answered Mar 26 '16 at 13:16

chepner

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It's best to assign the value with `eval` to some variable before printing: `eval val=\$$FOOBAR; echo "$val"`. In your case the argument is not quoted. Also, I was thinking about `FOOBAR=$(echo "$FOOBAR" | tr -dc [:alnum:]_); eval val=\$$FOOBAR`. Or `[ "$FOOBAR" != "$(echo "$FOOBAR" | tr -dc [:alnum:]_)" ] && eval ...` (or terminate the script right away). But your solution is a bit better (always start with alpha). – x-yuri Jun 29 '22 at 13:44

score 1 · Answer 2 · answered Mar 26 '16 at 13:17

For POSIX portability, you are pretty much left with

eval echo \$$variable

The usual caveats apply; don't use eval if the string you pass in is not completely and exclusively under your own control.

I lowercased your example; you should not be using upper case for your private variables, as uppercase names are reserved for system use.

in POSIX shell, how to print the value of the value of a variable

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