[ale] Bash confusion

[The Don Lachlan]

On Wed, Jul 20, 2011 at 04:13:39PM -0400, Geoffrey Myers wrote:
> The Don Lachlan wrote:
> > On Wed, Jul 20, 2011 at 03:29:42PM -0400, Al Snow wrote:
> >> Try if [ "X01" = "X${date}" ] then if $date is empty you still have "X".
> > 
> > That is unnecessary and confusing.
> > 
> >   if [ "01" = "$date" ]
> > 
> > is simpler and more clear.
> 
> Not that I agree with the "X01" approach, but it is a standard practice 
> throughout a lot of the scripting in Linux.

Yes, I'm aware. Sometimes, people get paid to write unnecessary and
confusing code. :)

Personally, it's also frustrating because Al followed up to my post by
suggesting something that I had explained was unnecessary.

-L


> >>> Date: Wed, 20 Jul 2011 15:22:40 -0400
> >>> From: ale-at-ale.org at unpopularminds.org
> >>> To: ale at ale.org
> >>> Subject: Re: [ale] Bash confusion
> >>>
> >>> On Wed, Jul 20, 2011 at 01:04:10PM -0400, Brian MacLeod wrote:
> >>>> You are doing a string comparison here, so you should take the correct
> >>>> precautions:
> >>>>> if [ $date = "01" ];
> >>>> should be like this:
> >>>> if [ "01" = "$date" ];
> >>>> Why?
> >>>> If for some ungodly reason your variable ends up as null, the whole
> >>>> statement (and function, etc) breaks if you have that null in front of
> >>>> the equal sign.  Flip that around and it "properly" evaluates even if
> >>>> null. Otherwise you'll see things like "unary operator" and such.
> >>>> The other thing is making sure you treat your variable as a string,
> >>>> thus, quote it so that you are sure it isn't being further evaluated
> >>>> and/or evaluated differently.
> >>> Order is irrelevent; quoting the string protects against null values.
> >>>
> >>>   if [ "$date" = "01" ]
> >>>
> >>> is safe, while
> >>>
> >>>   if [ "01" = $date ]
> >>>
> >>> fails if $date is a null string.
> >>>
> >>>
> >>> Regarding the original problem, as written, yes, it should work. But...
> >>>
> >>> Are there any commands between the date command and the test? There's no
> >>> explicit path used to date - could it be executing a different version of
> >>> date which is evaluating improperly? IOW, what are you telling us? ;)
> >>>
> >>> -L
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> 
> -- 
> Until later, Geoffrey
> 
> "I predict future happiness for America if they can prevent
> the government from wasting the labors of the people under
> the pretense of taking care of them."
> - Thomas Jefferson
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