[NTLUG:Discuss] What scripting change do I need to make?

[Patrick R. Michaud]

On Mon, Oct 05, 2015 at 09:46:08PM -0500, Leroy Tennison wrote:
> If only there was a way to tell mkdir "this isn't a string!".

It's important to note that mkdir(1) itself never sees quotes, braces,
or anything like that -- all of these expansions and substitutions
are handled by the shell *before* the mkdir command is ever called.

So, according to the bash(1) man page ("EXPANSIONS"):

   The order of expansions is: brace expansion; tilde expansion, parameter
   and  variable expansion, arithmetic expansion, and command substitution
   (done in a left-to-right fashion); word splitting; and pathname 
   expansion.

Thus, in the case of

     mkdir -p test/{`seq -s, 1 3`}

the brace expansion occurs before the command substitution.  Since
the part inside the braces doesn't have any bare commas in it, the
result of the command line after performing brace expansion is:

    mkdir -p test/`seq -s, 1 3`

and after performing command substitution the command line becomes

    mkdir -p test/1,2,3

The mkdir command then receives the "-p" and "test/1,2,3" arguments.

Try the above using echo(1) instead of mkdir(1) and you'll see what
I mean.  :-)

Pm


On Mon, Oct 05, 2015 at 09:46:08PM -0500, Leroy Tennison wrote:
> Thanks for asking, the original thinking was concerning building a
> "calendar" tree.  There are (usually compliance-related) situations where
> documents as proof of activities are required daily. Something like 'mkdir
> -p 2016/{Jan,Feb,Mar,Apr,May,Jun,Jul,Aug,Sep,Oct,Nov,Dec}/{`seq -s, 1 31`}'
> would produce a year's structure (and, of course, changing 2016 t0
> {2016,2017,2018} could produce multi-year - that's if `seq ...` would work).
> Granted, you have to remove 31 for five months and 30 along with (usually)
> 29 for February but that's small "retrofit" for a calendar year's worth of
> structured directory creation.
> 
> What I've discovered about the problem is that I can get the undesired
> results with 'mkdir -p test/{'1,2,3'}' which leads me to believe that
> possibly the problem is that the `seq ...` substitution is causing mkdir to
> believe it's a string (even though the return of `seq ...` contains no
> quotes).  The same thing happens with $variable.
> 
> Yes, I could use progressive 'for ...' loops but I was hoping for something
> simple (it's known as being lazy...).  If only there was a way to tell mkdir
> "this isn't a string!".
> 
> On 10/05/2015 12:44 AM, Robert Citek wrote:
> >I find your original version using braces more readable. What's your
> >rationale for wanting to use seq?
> >
> >Regards,
> >- Robert
> >
> >On Saturday, October 3, 2015, Leroy Tennison <leroy.tennison at verizon.net>
> >wrote:
> >
> >>Thanks, that works (had to refresh my printf understanding).
> >>
> >>On 10/03/2015 04:31 AM, Patrick R. Michaud wrote:
> >>
> >>>How about...?
> >>>
> >>>      mkdir -p `seq -f "test/%g" 1 3`
> >>>
> >>>Pm
> >>>
> >>>On Sat, Oct 03, 2015 at 12:36:25AM -0500, Leroy Tennison wrote:
> >>>
> >>>>Using
> >>>>
> >>>>      mkdir -p test/{1,2,3}
> >>>>
> >>>>creates test/1, test/2 and test/3 as expected.  However
> >>>>
> >>>>      mkdir -p test/{`seq -s, 1 3`}
> >>>>
> >>>>creates test/{1,2,3}
> >>>>
> >>>>What do I need to do to get the "seq" variant to produce the same result
> >>>>as
> >>>>the first command?
> >>>>
> >>>>
> >>>>_______________________________________________
> >>>>http://www.ntlug.org/mailman/listinfo/discuss
> >>>>
> >>>_______________________________________________
> >>>http://www.ntlug.org/mailman/listinfo/discuss
> >>>
> >>>
> >>_______________________________________________
> >>http://www.ntlug.org/mailman/listinfo/discuss
> >>
> >_______________________________________________
> >http://www.ntlug.org/mailman/listinfo/discuss
> >
> 
> 
> _______________________________________________
> http://www.ntlug.org/mailman/listinfo/discuss