Re: Bash true/false builtings undocumented? "false" not working?

[Greg Wooledge <wooledg@eeg.ccf.org>]

On Fri, Aug 17, 2018 at 06:46:54PM +1000, Zenaan Harkness wrote:
> $ test $? && echo ok || echo error $?

Others have already pointed out that  test $?  is not what you think it
is.  When the test command is given 1 argument, it tests that argument's
string length.  If the string length is 0, then it's false.  If the
string length is non-zero, then it's true.

The string length of $? is always non-zero, so  test $?  is always true.

But what I really wanted to point out is that the  x && y || z  construct
is BROKEN and WRONG.  See <https://mywiki.wooledge.org/BashPitfalls#pf22>
for the verbose explanation.


On Fri, Aug 17, 2018 at 07:29:47PM +1000, Zenaan Harkness wrote:
> Is there a "cleaner" way to test the true/ error exit status other
> than using "$?", with bonus points for working in posix sh as well as
> Bash, ?

Simply use "if" like you're supposed to.

if mycommand arg1 arg2; then
  echo "it worked"
else
  echo "it failed"
fi

Or, if you only care about one of the two cases, you may use EITHER
the && or the || operator.  Just never, ever use both of them in the
same compound command.

mycommand arg1 arg2 || die "whoopsie"