How to manually expand a special variable (ex: ~ tilde) in bash

Question

I have a variable in my bash script whose value is something like this:

~/a/b/c

Note that it is unexpanded tilde. When I do ls -lt on this

Answer 1

Simplest: replace 'magic' with 'eval echo'.

$ eval echo "~"
/whatever/the/f/the/home/directory/is

Problem: You're going to run into issues with other variables because eval is evil. For instance:

$ # home is /Users/Hacker$(s)
$ s="echo SCARY COMMAND"
$ eval echo $(eval echo "~")
/Users/HackerSCARY COMMAND

Note that the issue of the injection doesn't happen on the first expansion. So if you were to simply replace magic with eval echo, you should be okay. But if you do echo $(eval echo ~), that would be susceptible to injection.

Similarly, if you do eval echo ~ instead of eval echo "~", that would count as twice expanded and therefore injection would be possible right away.