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From: Kenny McCormack on 20 Jun 2010 11:24
Currently, I use case/esac to test to see if a string starts with a dash:

case $1 in
case -*) ...
esac

But it would be more convenient to be able to do it with "test" syntax,
i.e.:

[ $1 {something} - ]

I think there is some syntax to do that, but I don't know it.

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From: pk on 20 Jun 2010 11:17
Kenny McCormack wrote:

> Currently, I use case/esac to test to see if a string starts with a dash:
>
> case $1 in
> case -*) ...
> esac
>
> But it would be more convenient to be able to do it with "test" syntax,
> i.e.:
>
> [ $1 {something} - ]
>
> I think there is some syntax to do that, but I don't know it

With bash, this seems to work:

a='-foo'

if [[ "$a" =~ ^- ]]; then
echo "$a starts with a dash"
fi

also this works:

if [[ "$a" == -* ]]; then
....
From: John Kelly on 20 Jun 2010 11:47
On Sun, 20 Jun 2010 15:24:42 +0000 (UTC), gazelle(a)shell.xmission.com
(Kenny McCormack) wrote:

>Currently, I use case/esac to test to see if a string starts with a dash:
>
>case $1 in
>case -*) ...
>esac
>
>But it would be more convenient to be able to do it with "test" syntax,
>i.e.:
>
>[ $1 {something} - ]
>
>I think there is some syntax to do that, but I don't know it.

Notice this:

ts=abc; [ '-' == "${ts:0:1}" ] && echo $?
(does not echo)

ts=-abc; [ '-' == "${ts:0:1}" ] && echo $?
0



The offset 0 (first character in string) can trip you up though, the
bash man page says:

>Substring indexing is zero-based unless the positional parameters
>are used, in which case the indexing starts at 1.




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From: Martin Vaeth on 20 Jun 2010 11:53
Kenny McCormack <gazelle(a)shell.xmission.com> wrote:
> Currently, I use case/esac to test to see if a string starts with a dash:
> [..]
> But it would be more convenient to be able to do it with "test" syntax,
> i.e.:
>
> [ $1 {something} - ]
>
> I think there is some syntax to do that, but I don't know it.

[ "${1%-}" != "$1" ]

But why should "test" be more convenient when
you can also use "case" as part of an "if" or
also in && or || chains:

if ! case $1 in -*) false;; esac
then echo "$1 starts with -"
fi

case $1 in -*) false;; esac || echo "$start with -"
From: John Kelly on 20 Jun 2010 12:04
On 20 Jun 2010 15:53:54 GMT, Martin Vaeth
<vaeth(a)mathematik.uni-wuerzburg.de> wrote:

>case $1 in -*) false;; esac || echo "$start with -"

I think that's harder to read. I had to test it to be sure it worked.


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