Parameter Expansion

Parameter Expansion

[Clint Priest]

[-- Attachment #1: Type: text/plain, Size: 396 bytes --]

Having trouble getting nested parameter substitution working again, how 
can these two lines be correctly merged into a single line:

     FUNCS=( $SD/autoload/*);
     FUNCS=${(@)FUNCS:t};

Assume for arguments sake that SD is a working directory with an 
autoload directory and autoload has one file in it (named pv).

The above two lines together properly produce ( pv ).

Thanks,

-- 
-Clint

Re: Parameter Expansion

[Bart Schaefer]

On Sun, Aug 13, 2017 at 3:58 PM, Clint Priest <cpriest@rxv.me> wrote:
> Having trouble getting nested parameter substitution working again, how can
> these two lines be correctly merged into a single line:
>
>     FUNCS=( $SD/autoload/*);
>     FUNCS=${(@)FUNCS:t};

You're mixing globbing with parameter substitution.  Due to order of
operations (parameters before globs -- otherwise $SD/autoload/* would
not work) you can't do this via substitution.

Fortunately there are a lot of things you can do with globbing that
mimic parameter substitution, and :t happens to be one of them; you
can use it as a glob qualifier:

FUNCS=( $SD/autoload/*(:t) )

Re: Parameter Expansion

[Bart Schaefer]

On Sun, Aug 13, 2017 at 4:51 PM, Bart Schaefer
<schaefer@brasslantern.com> wrote:
>
> FUNCS=( $SD/autoload/*(:t) )

Oh, and if you want something more complicated, the above is
equivalent to using the "e" glob qualifier like so:

  $SD/autoload/*(e?'reply=( "$REPLY:t" )'?)

So you can do any substitution tricks you want on $REPLY.  Just
remember that it will contain exactly one filename at a time.

Re: Parameter Expansion

[Clint Priest]

On 8/13/2017 7:07 PM, Bart Schaefer wrote:
>> FUNCS=( $SD/autoload/*(:t) )
Wow, it never dawned on me that I could just use it as a glob 
qualifier.  I'd be trying to do it with ${~..} and ${~~..} with no luck.

Thank you!
> Oh, and if you want something more complicated, the above is
> equivalent to using the "e" glob qualifier like so:
>
>    $SD/autoload/*(e?'reply=( "$REPLY:t" )'?)
>
> So you can do any substitution tricks you want on $REPLY.  Just
> remember that it will contain exactly one filename at a time.
I've read about but not yet played around with the e flag yet, but I've 
heard of it. :)

Thanks again Bart!

-- 
-Clint

Parameter expansion

[Roland Jesse]

The zsh manual says regarding to parameter expansion:

  ${+name} 
    If name is the name of a set parameter `1' is substituted, otherwise `0' is
    substituted.

But why do I do get the following than?

% if [ ! ${+BLURB} ]; then
then> echo "BLURB not set"
then> else
else> echo "BLURB set"
else> fi
BLURB set
% 

I was expecting the opposite. Curiously:


% export BLURB=foo
% if [ ! ${+BLURB} ]; then
echo "BLURB not set"
else
echo "BLURB set"
fi
BLURB set
%

Maybe the question should be: How do you check whether or not an
environment variable is set?

Comments are appreciated.

	Roland

Re: Parameter expansion

[Peter Stephenson]

Roland Jesse wrote:
> But why do I do get the following than?
> 
> % if [ ! ${+BLURB} ]; then
> then> echo "BLURB not set"
> then> else
> else> echo "BLURB set"
> else> fi
> BLURB set
> % 

That's becuase

% if [ ! 0 ]; then print no; else print yes; fi
yes
% if [ ! 1 ]; then print no; else print yes; fi
yes

It's testing whether the string has length zero, which it doesn't.  You
need arithmetical evaluation; change the [ to (( and the ] to )) and
everything should work.

-- 
Peter Stephenson <pws@ibmth.df.unipi.it>       Tel: +39 050 844536
WWW:  http://www.ifh.de/~pws/
Dipartimento di Fisica, Via Buonarroti 2, 56127 Pisa, Italy

Re: Parameter expansion

[Bart Schaefer]

On Apr 1,  8:20am, Rob Hooft wrote:
} Subject: Re: Parameter expansion
}
} I understand this is a zsh mailinglist, but I find the shell-independent
} 
}   xargs zip backup.zip < index.txt
} 
} more readable, and it gracefully handles the case where index.txt is too
} long for the command line....

Zsh can handle VERY long command lines ... much longer than required to
hold the number of arguments xargs will pass to a single command by
default.  Does

	zip backup.zip file1 file2 ... fileN
	zip backup.zip fileN+1 fileN+2 ... file2N

really do the right thing?  Because that's roughly what'll get executed
if there are enough lines in index.txt.  Even if zip does the right thing
in that case, "xargs tar zcf backup.tar" is a recipe for disaster.

Finally, the whole point of the question was that index.txt contains
file _patterns_, not file names; xargs, by design, won't expand file
patterns, so your solution would fail completely.

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com

Re: Parameter expansion

[Geoff Wing]

Rob Hooft <r.hooft@euromail.net> typed:
:>>>>> "BS" == Bart Schaefer <schaefer@brasslantern.com> writes:
: BS> On Mar 31, 6:04pm, Mircea Damian wrote: } Subject: Re: Parameter
: BS> expansion } } On Wed, Mar 31, 1999 at 02:54:01PM +0000, Geoff
: BS> Wing wrote: } > Mircea Damian <dmircea@kappa.ro> typed: } > :zip
: BS> backup.zip $(<index.txt) } > } > zip backup.zip $(eval echo
: BS> $(<index.txt))
: BS> eval zip backup.zip $(<index.txt)
: BS> zip backup.zip ${~$(<index.txt)}
:I understand this is a zsh mailinglist, but I find the shell-independent
:  xargs zip backup.zip < index.txt
:more readable, and it gracefully handles the case where index.txt is too
:long for the command line....

Yep, though Bart's example ``zip backup.zip ${~$(<index.txt)}'' handles
the case where names have spaces in them.

Regards,
-- 
Geoff Wing   <gcw@pobox.com>            Mobile : (Australia) 0412 162 441
Work URL: http://www.primenet.com.au/   Ego URL: http://pobox.com/~gcw/

Re: Parameter expansion

[Rob Hooft]

>>>>> "BS" == Bart Schaefer <schaefer@brasslantern.com> writes:

 BS> On Mar 31, 6:04pm, Mircea Damian wrote: } Subject: Re: Parameter
 BS> expansion } } On Wed, Mar 31, 1999 at 02:54:01PM +0000, Geoff
 BS> Wing wrote: } > Mircea Damian <dmircea@kappa.ro> typed: } > :zip
 BS> backup.zip $(<index.txt) } > } > zip backup.zip $(eval echo
 BS> $(<index.txt))

 BS> eval zip backup.zip $(<index.txt)

 BS> zip backup.zip ${~$(<index.txt)}

I understand this is a zsh mailinglist, but I find the shell-independent

  xargs zip backup.zip < index.txt

more readable, and it gracefully handles the case where index.txt is too
long for the command line....

-- 
=====   R.Hooft@EuroMail.net   http://www.xs4all.nl/~hooft/rob/  =====
=====   R&D, Nonius BV, Delft  http://www.nonius.nl/             =====
===== PGPid 0xFA19277D ========================== Use Linux! =========

Re: Parameter expansion

[Bart Schaefer]

On Mar 31,  6:04pm, Mircea Damian wrote:
} Subject: Re: Parameter expansion
}
} On Wed, Mar 31, 1999 at 02:54:01PM +0000, Geoff Wing wrote:
} > Mircea Damian <dmircea@kappa.ro> typed:
} > :zip backup.zip $(<index.txt)
} > 
} > zip backup.zip $(eval echo $(<index.txt))

eval zip backup.zip $(<index.txt)

zip backup.zip ${~$(<index.txt)}

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com

Re: Parameter expansion

[Mircea Damian]

On Wed, Mar 31, 1999 at 02:54:01PM +0000, Geoff Wing wrote:
> Mircea Damian <dmircea@kappa.ro> typed:
> :I want to create an archive for the files that are matched by the contents of
> :index.txt
> :I tried in dir/ to run the command:
> :zip backup.zip $(<index.txt)
> 
> zip backup.zip $(eval echo $(<index.txt))

Yess.. of course. And it's obvious! Thanks a lot!

-- 
Mircea Damian
Network Manager
dmircea@roedu.net, dmircea@lbi.ro, dmircea@kappa.ro
MD65-RIPE, MD2225, MD1-6BONE

Re: Parameter expansion

[Geoff Wing]

Mircea Damian <dmircea@kappa.ro> typed:
:I want to create an archive for the files that are matched by the contents of
:index.txt
:I tried in dir/ to run the command:
:zip backup.zip $(<index.txt)

zip backup.zip $(eval echo $(<index.txt))

:but that didn't worked because the file* another* weren't expanded. How do
:I tell him(zsh 3.1.5) to expand the result of $(<index.txt)?

-- 
Geoff Wing   <gcw@pobox.com>            Mobile : (Australia) 0412 162 441
Work URL: http://www.primenet.com.au/   Ego URL: http://pobox.com/~gcw/

Parameter expansion

[Mircea Damian]

Hello,

I need some help here and maybe someone of you can help.

Supposing that I have this directory structure:

dir -+- backup -+- file.1
     |          +- file.2
     |          +- anotherfile.txt
     |          +- dont_backup
     +- index.txt

And index.txt is:
file*
another*

I want to create an archive for the files that are matched by the contents of
index.txt


I tried in dir/ to run the command:

zip backup.zip $(<index.txt)

but that didn't worked because the file* another* weren't expanded. How do
I tell him(zsh 3.1.5) to expand the result of $(<index.txt)?

Thanks!

-- 
Mircea Damian
Network Manager
dmircea@roedu.net, dmircea@lbi.ro, dmircea@kappa.ro
MD65-RIPE, MD2225, MD1-6BONE