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

Question

I have defined the following variable:

myVar=true 

now I'd like to run something along the lines of this:

if [ myVar ] then     echo "true" else     echo "false" fi 

The above code does work, but if I try to set

myVar=false 

it will still output true. What might be the problem?

edit: I know I can do something of the form

if [ "$myVar" = "true" ]; then ... 

but it is kinda awkward.

Thanks

Answer 1

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 /