Re: test z$foo = zbar (and Re: [PATCH 1/3] bisect: relax requirement for a working tree.)

[Stefano Lattarini <stefano.lattarini@gmail.com>]

On Sunday 07 August 2011, Jonathan Nieder wrote:
> Am I the only one who finds this
> 
> 	test "z$foo" = "zbar"
> 
> style to be impossibly ugly?  It means every time someone considers
> using the "test" utility, they decide "is this expression likely to
> looks like an operator" and each time someone reads a use of the
> "test" utility, there is a lingering question of whether that choice
> was made correctly.  By contrast, if one follows the following simple
> rules, everything works fine with the shells git supports:
> 
>  - _Do_ use the "z$foo" trick when using expr.
>  - Do not use test's '(', '),' -a and -o operators; use && and ||
>    instead.
> 
> The Autoconf manual says
> 
> 	Posix also says that ‘test ! "string"’, ‘test -n "string"’ and
> 	‘test -z "string"’ work with any string, but many shells (such
> 	as Solaris, AIX 3.2, UNICOS 10.0.0.6, Digital Unix 4, etc.)
> 	get confused if string looks like an operator:
> 
> Notice that none of the mentioned shells is close enough to POSIX even
> to support $( / ).  This is an area in which early POSIX work improved
> shells immensely (the "-e" primary was introduced around the same
> time).
>
While this is true, some problems with the `test' builtin persists also
with in more "posixy" shells.  For example, with Solaris /bin/ksh and
/usr/xpg4/bin/sh (the latter expected to be the default POSIX-compliant
shell on the system, since as you've noticed /bin/sh is defintely not
compliant there), one sees:

  $ /usr/xpg4/bin/sh -c 'test -z ")"'; echo $?
  0
  $ /bin/ksh -c 'test -z ")"'; echo $?
  0

This will be documented in the next version of the Autoconf manual BTW.

Regards,
  Stefano