[ means test right? Maybe? (was: Re: GOTCHA in Ubuntu - broken shell)

[Tom Buskey]

On 10/1/07, Flaherty, Patrick <pflaherty at wsi.com> wrote:
>
> > =>The band-aid, by the way, was that "=" instead of "==" works.
> > =>(And how ugly is THAT? And how do you explain that to a student?)
> >
> > FYI, the correct operator is = and == is an extension of bash. ==
> should
> > not be used.
> >
>
> I thought everything in those brackets was just an argument to test. The
> = or == shouldn't be dependant on your shell, but on your coreutils
> version.
>
> However, I tested it.
> pack at dco-pflahertylx:~/hack$ cat test.dash
> #!/bin/dash
>
> t="X"
>
> if [ "$t" == "X" ]; then
> echo $t;
> else
> echo "Not X"
> fi
> pack at dco-pflahertylx:~/hack$ dash test.dash
> [: 9: ==: unexpected operator
> Not X
> pack at dco-pflahertylx:~/hack$ bash test.dash
> X
>
> ...and now my world is turned upside down.
>
> Anyone know why this works that way?



It sounds like dash is breaking lots of people's assumptions.

I do a man test on Fedora 7 and it does not show ==.  On Solaris 10, it has
an example of == for csh.

Man bash & ksh on Fedora 7 shows == for both.  bash on Solaris shows == for
bash, but nothing for ksh.

And of course, [ is a builtin whereas test is /bin/test.  Linux has
/usr/bin/[ so you could be explicit, but most shells substitute their
builtin [.

Here's the relevant bash (3.2.9) man page on Fedora 7:


      string == pattern
              True,  if  string  matches  pattern.  Any part of pattern can
be
              quoted to cause it to be matched as a string.  With a
successful
              match  to  a  pattern, the .sh.match array variable will
contain
              the match and sub-pattern matches.
       string = pattern
              Same as == above, but is obsolete.

And Solaris (bash 3.00.16):
 string1 == string2
          True if the strings are equal.  = may be used in  place
          of == for strict POSIX compliance.

Sounds like dash isn't fully cooked.  == is used & works in ksh, bash and
sh.
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