Re: [gentoo-dev] Re: Re: RFC: sh versionator.eclass

[Roy Marples]

On Tue, 2007-10-02 at 19:37 +0100, Steve Long wrote:
> Roy Marples wrote:
> > With [[ ]] you don't need to quote, which encourages people not to
> > bother learning when and when not to quote.
> >
> Ugh, that is so untrue imo. In #bash most people don't know [[ and use [
> without quoting, as well as leaving out quotes elsewhere. Which is why we
> beat them over the head about quoting _all_ the time (!quotes in #bash [1])

You should always quote when using [ - the only exception you can ever
make is when using something like $? or $# as that is always a number.

>
> > Regular readers of -dev will also notice a large amount of people not
> > quoting correctly, my view is that bash encourages this through the use
> > of [[ ]].
> >
> A lot of those have been stuff like cd $S (when S could have spaces
> according to where the tmp dir is located) and the like, ie stuff outside
> [[. Honestly, [[ has got little to do with learning about quoting, since
> the typical case where quoting is missing is when a path is passed to a
> command. The thing to learn is that the shell expands everything before
> passing it to a command, and that spaces will lead to two parameters where
> you thought you had one, unless you use quotes. (ie cd "$S" )

Everything in shell IS a command with the exception of variable
assignment. Why do you think [ exist in /usr/bin?

Once you think "everything is a command" then quoting becomes a lot
easier. [[ ]] removes this concept.

> Inside [[ is similar to assignment, in that it's down to the lex/parse (eg
> a='  omg spaces!'; b='oh Noes! '$a; echo "$b"  # works fine -- but note
> what happens when you echo $b with no quotes.) kojiro knows more about the
> corner cases where quoting is needed in [[, but it _never_ shields you from
> quoting issues outside tests, and you *will* be told about it if you paste
> an unsafe loc in #bash. (We don't care if that's not the current problem as
> you see it: if you're not quoting right, your scripts are worse than
> useless, since they'll break when your users least expect it, for no
> apparent reason, and you're nowhere to be found. People soon learn not to
> paste unsafe expansions ;p and they get into the habit of always quoting.)
>
> [1] USE MORE QUOTES! Read
> http://bash-hackers.org/wiki/doku.php?id=syntax:words to understand why.
> http://www.grymoire.com/Unix/Quote.html will tell you how. -- Optimally,
> you should quote every parameter expansion ($foo).

So in other words, [ ] always needs quotes whereas [[ ]] normally
doesn't but could need quotes in corner cases.

I know which I'd prefer - certainty over uncertainty.

Thanks

Roy

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