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

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

User · Answer

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    esac   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

User · Answer

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

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

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