OT: Re: command-line vs. script file

Chris F.A. Johnson wrote:
> On Sun, 15 May 2005 at 13:21 GMT, Ed Morton wrote:
> 
>
>
>     There's nothing wrong with "-" in a filename, except at the
>     beginning.

Any time you have to say "except..." there is a problem.

The POSIX portable filename standard allows letters,
>     numbers, periods, hyphens and underscores, but a name may not
>     begin with a hyphen.
>

We often write scripts that manipulate file names, holding parts of the
name in variables, creating tmp file names from the parts, etc. so the
impact of a hyphen isn't restricted to where it appears in the original
file name.

I agree you can later code to avoid the potential problems introduced by
"-"s, but if you just choose to avoid them when creating the files then
you don't need to deal with them at all.

Ed

In article <ta6dnY-rs8WWHRrfRVn-1w@comcast.com>,
Ed Morton  <morton@lsupcaemnt.com> wrote:
...
>We often write scripts that manipulate file names, holding parts of the
>name in variables, creating tmp file names from the parts, etc. so the
>impact of a hyphen isn't restricted to where it appears in the original
>file name.

Exactly.  That's the point.

On Sun, 15 May 2005 at 16:59 GMT, Ed Morton wrote:
>
>
> Chris F.A. Johnson wrote: 
>
> Any time you have to say "except..." there is a problem.
>
> The POSIX portable filename standard allows letters, 
>
> We often write scripts that manipulate file names, holding parts of the
> name in variables, creating tmp file names from the parts, etc. so the
> impact of a hyphen isn't restricted to where it appears in the original
> file name.
>
> I agree you can later code to avoid the potential problems introduced by
> "-"s, but if you just choose to avoid them when creating the files then
> you don't need to deal with them at all.

When is a hyphen a problem, except at the beginning of a
filename?

--
Chris F.A. Johnson                     <http://cfaj.freeshell.org>
 ========================================
==========================
Shell Scripting Recipes: A Problem-Solution Approach, 2005, Apress
<http://www.torfree.net/~chris/books/ssr.html>

Chris F.A. Johnson wrote:
> On Sun, 15 May 2005 at 16:59 GMT, Ed Morton wrote:
> 
>
>
>      When is a hyphen a problem, except at the beginning of a
>      filename?
>

As a trivial example:

$ file=a-b
$ tmp="${file#[a-z]}"
$ > $tmp
$ rm $tmp
rm: invalid option -- b
Try `rm --help' for more information.

Had I instead used underscores in the name of "file":

$ file=a_b
$ tmp="${file#[a-z]}"
$ > $tmp
$ rm $tmp

The hyphen was not at the start of the original file name but by
manipulation to produce a tmp file, it ended up at the front of the tmp
file name and so became a problem.

Regards,

Ed.