bash if -a vs -e option

Question

Both about -a and -e options in Bash documentation is said:

-a file
    True if file exists.
-e file
    True if file exists. 
         


        

Answer 1

The double bracket [[ exp ]] is a bash builtin. In bash -a and -e are the same, probably for some backwards compatibility.

The single bracket [ exp ] is an alias for the external command "test". In "test", -a is a logical AND. Although [ nothing AND $STRING ] looks like it should be false, test has some syntax quirks, which is why I recommend using the bash builtin [[ exp ]], which tends to be more sane.

Note: bash really does call /bin/[ when you use "[".

$ [ $UNASIGNED_VAR == "bar" ]
bash: [: ==: unary operator expected

the error shows bash called [. An strace also shows "execve("/usr/bin/[", ..."