Lookup shell variables by name, indirectly

Question

Let's say I have a variable's name stored in another variable:

myvar=123
varname=myvar

now, I'd like to get 123 by just using $varname variable. Is there a direct way for that? I found no such bash builtin for lookup by name, so came up with this:

function var { v="\$$1"; eval "echo "$v; }

so

var $varname  # gives 123

Which doesn't look too bad in the end, but I'm wondering if I missed something more obvious. Thanks in advance!

Answer 1

From the man page of bash:

${!varname}

If the first character of parameter is an exclamation point, a level of variable indirection is introduced. 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.

Answer 2

There isn't a direct Posix-conforming syntax, only a bashism. I usually do this:

eval t=\$$varname

This will work on any Posix shell, including those systems where bash is the login shell and /bin/sh is something smaller and faster like ash. I like bash and use it for my login shell but I avoid bashisms in command files. One problem with writing bash-specific scripts is that even if you can count on bash being installed, it could be anywhere on the path. It might be a good idea in that case to use the fully general /usr/bin/env shebang style, but note that this is still not 100% portable and has security issues.

Answer 3

${!varname} should do the trick

$ var="content"
$ myvar=var
$ echo ${!myvar}
content

Answer 4

I usually look at Advance Bash-Scripting Guide when I need to freshen up my Bash skills.

Regarding your question look at Indirect References

Notation is:

Version < 2
\$$var

Version >= 2
${!varname}