How to evaluate a boolean variable in an if block in bash?

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bash doesn't know boolean variables, nor does test (which is what gets called when you use [ ).

A solution would be:

if $myVar ; then ... ; fi
because true and false are commands that return 0 or 1 respectively which is what if expects.
Note that the values are "swapped". The command after if must return 0 on success while 0 means "false" in most programming languages.
SECURITY WARNING: This works because BASH expands the variable, then tries to execute the result as a command! Make sure the variable can't contain malicious code like rm -rf /
                The case answer (from @Jens) is safer and doesn't require a fork to test a simple variable.
– Mark Lakata
                Sep 22, 2015 at 17:22
Note that the if $myVar; then ... ;fi construct has a security problem you might want to avoid with
case $myvar in
  (true)    echo "is true";;
  (false)   echo "is false";;
  (rm -rf*) echo "I just dodged a bullet";;
You might also want to rethink why if [ "$myvar" = "true" ] appears awkward to you. It's a shell string comparison that beats possibly forking a process just to obtain an exit status. A fork is a heavy and expensive operation, while a string comparison is dead cheap. Think a few CPU cycles versus several thousand. My case solution is also handled without forks.
                true and false are built-in commands in most shells. Invoking them is unlikely to require a fork() call.
– Keith Thompson
                Sep 22, 2015 at 17:40
                Calling which true in bash, zsh, ksh, dash, and fish, it seems that only zsh has true and false as built-ins. Seems like a sensible thing for shells to implement though!
– Christopher Shroba
                Sep 13, 2020 at 13:39
                don't use which -- that only searches the $PATH -- use type -a true -- true and false are builtin to bash and ksh and dash
– glenn jackman
                Sep 13, 2020 at 20:15