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 '-a' option to the test operator has one meaning as a unary operator and another as a binary operator. As a binary operator, it is the 'and' connective (and '-o' is the 'or' connective). As a unary operator, it apparently tests for a file's existence.

The autoconf system advises you to avoid using '-a' because it causes confusion; now I see why. Indeed, in portable shell programming, it is best to combine the conditions with '&&' or '||'.

I think @litb is on the right track. When you have '! -a ${resin_dir}', Bash may be interpreting it as "is the string '!' non-empty and is the string in '${resin_dir}' non-empty, to which the answer is yes. The Korn shell has a different view on this, and the Bourne shell yet another view - so stay away from '-a'.

On Solaris 10:

$ bash -c 'x=""; if [ ! -a "$x" ] ; then echo OK ; else echo Bad; fi'
Bad
$ ksh -c 'x=""; if [ ! -a "$x" ] ; then echo OK ; else echo Bad; fi'
OK
$ sh -c 'x=""; if [ ! -a "$x" ] ; then echo OK ; else echo Bad; fi'
sh: test: argument expected
$