Re: Inconsistent behavior between ! [ -a /bin/bash ] and [ ! -a /bin/bash ]

[Paul Jarc]

cromwell@dp.2y.net wrote:
>       if  !  [  -a  /bin/bash  ];  echo  "bash not found";  fi
>       if  [  !  -a  /bin/bash  ];  echo  "bash not found";  fi
>       Both should produce no output, because of course I have bash,
>         but the 2nd line prints  "bash not found"

It looks like the "-a" argument is interpreted as the binary "and"
operator, and the "!" and "/bin/bash" are tested for being nonempty
strings, so the result is true.  It's generally best to keep [ ]
expressions as simple as possible and move negations, ands, and ors
outside them, using "!", "&&", and "||".  The parsing of [ ]
expressions is not always well-defined, and even when it is, it won't
necessarily be what you expect.


paul