test -n "${var+set}"?

[Derek Robert Price]

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Hey all,

Just wondering what the logic behind all the constructs like, `test
"${var+set} = set', was in recently generated configure scripts.  Is it
just a carryover from the old days when someone on the autoconf team
thought test -n/-z wasn't portable?  Is it just someone's preference?
Is this construct overkill: `if test -n "${ZSH_VERSION+set}"'?

All I could find in the Autoconf manual was the following:

     Contrary to a common belief, `test -n STRING' and `test -z STRING'
     *are* portable.  Nevertheless many shells (such as Solaris 2.5,
     AIX 3.2, UNICOS 10.0.0.6, Digital Unix 4 etc.) have bizarre
     precedence and may be confused if STRING looks like an operator:

          $ test -n =
          test: argument expected

Does this mean that if $var EXPANDS to `=' that some shells will break?
Or does the `=' need to be a literal?

Trying to write shell portably,

Derek

- --
                *8^)

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