Re: initialisation bash variables

[Francky Leyn]

On 8/16/2011 10:53 PM, Stephane CHAZELAS wrote:
> 2011-08-16, 22:24(+02), Francky Leyn:
> [...]
> > VAR=FALSE
> > # some command line procesing, that can set VAR to "TRUE"
> > if [ $VAR = TRUE ]; then
> > ...
> > fi
> >
> > Must I effectively write that VAR=FALSE?
> > Or will the script work fine without?
>
> Yes, you must write it, because bash may inherit a VAR variable
> from the environment like I said (especially when you consider
> that all uppercase variables are by convention reserved for
> environment variables).

1) So it's a bad idea to use uppercase variables in a script?
2) If VAR coincides with an environment variable, and in the
   script I change it value, is this then propagated to outside
   the script? Is the environment variable affected?

> > Also, can't I write the test as
> >
> > if [ $VAR ]; then
> > ...
> > fi
> [...]
>
> No. That syntax is wrong.
>
> Valid syntaxes are:
>
> if [ "$VAR" != "" ]
>
> if [ -n "$VAR" ]
>
> if [ "$VAR" ]
>
> Or if you want to be extremely portable:
>
> if [ "" != "$VAR" ]
> or
> if [ "x$VAR" != x ]
>
> Personally, I prefer:
>
> var=false
> if ... var=true ...
>
> if "$var"; then
>    ...
> fi