Is !C: a valid environment variable?

[Igor Pechtchanski]

On Thu, 1 Apr 2004, Volker Quetschke wrote:

> Hi!
>
> If you start bash from a command prompt, e.g. by starting the
> cygwin.bat you get funny environment variables:
>
> bash-2.05b$ set | grep \!
> !C:='C:\cygwin\bin'
>
> When you exit bash and start it again from the same shell you can
> even get:
>
> bash-2.05b$ set | grep \!
> !C:='C:\cygwin\bin'
> !EXITCODE=00000000
>
> But try to echo any of these, or define one with !.
>
> bash-2.05b$ export !HELLO=hello
> bash: !HELLO=hello: event not found

'!' is a bash special character.  For a more meaningful error message, try
"export \!HELLO=hello".  However, I don't believe bash allows variable
names containing '!'...

> I think this special treatment is a bug, what is the prefered solution?

POSIX, however, does allow these names, i.e., the first argument to
putenv() can be an arbitrary string (containing everyting but '\0' and
'=', IIRC).

> The special treatment is done in environ.cc:
>
>    /* Current directory information is recorded as variables of the
>       form "=X:=X:\foo\bar; these must be changed into something legal
>       (we could just ignore them but maybe an application will
>       eventually want to use them).  */
>
> I'm asking because I have a programm that chokes on !<something>
> environment variables, and he workaround I'm using is always starting
> the shell via: C:\cygwin\bin\rxvt.exe -e /usr/bin/bash --login -i
> from the desktop or logoing into that machine via ssh.
>
> Volker

Another way of doing this is "env -i /bin/bash --login -i",
or, if you just want to unset the troublesome ones,
"env `set | sed -ne '/\!/{s/=.*$//; s/^/-u / p}'` bash --login -i".

HTH,
	Igor
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