Use of variables in the <x-y> globbing mechanism

Use of variables in the <x-y> globbing mechanism

[Henman]

It would be very useful if  the <x-y> globbing mechanism would work with 
variables.   I can't get it to work.  If it only accepts numeric 
constants, nothing can be done, but it would be an elegant solution to 
my problem of taking a slice of files out of a larger group for 
processing in a batch file.


I am trying to do this:   ( Where the Src FName Patter  SFNPAT gives the 
fname prefix and fname extension and the <01-15> specifies which slice 
of files to get.
# The from_number and to_number are read in from a list of files to process
     and injected between a filename pattern's prefix and extension.

    for file in ${SFNPAT:r}-<${from_number}-${to_number}>.${SFNPAT:e}
       do
           # processing goes here
       done

When I try the above script, I am greeted with a  " parse error near 
`<'"    error message.  This can be done otherways, I just wanted to 
know if the <X-Y> form could be used in some way to acheive this.

Thanks

Re: Use of variables in the <x-y> globbing mechanism

[Bart Schaefer]

On Apr 20, 10:24pm, Henman wrote:
} 
} It would be very useful if  the <x-y> globbing mechanism would work with 
} variables.

It can't do so because <$x-$y> is valid redirection syntax, meaning to
read from file "$x-$y" and write to whatever comes after.  It's rare
enough to have files with digit-digit names that it was deemed OK to
break the redirection rules in that special case, but it would cause
to many problems to generalize it.

} # The from_number and to_number are read in from a list of files to process
}      and injected between a filename pattern's prefix and extension.
} 
}     for file in ${SFNPAT:r}-<${from_number}-${to_number}>.${SFNPAT:e}

Use the {x..y} syntax:

    for file in ${SFNPAT:r}-{${from_number}..${to_number}}.${SFNPAT:e}

This latter expands to the full list of names rather than globbing them,
so it won't skip any missing files, but it will probably work in your
example.

If there may be gaps in the file sequence so you really do need to do
the glob, put the entire expression in a variable like so:

    local slice="<${from_number}-${to_number}>"
    for file in ${SFNPAT:r}-${~slice}.${SFNPAT:e}

Re: Use of variables in the <x-y> globbing mechanism

[Nikolay Aleksandrovich Pavlov (ZyX)]

21.04.2016, 10:18, "Bart Schaefer" <schaefer@brasslantern.com>:
> On Apr 20, 10:24pm, Henman wrote:
> }
> } It would be very useful if the <x-y> globbing mechanism would work with
> } variables.
>
> It can't do so because <$x-$y> is valid redirection syntax, meaning to
> read from file "$x-$y" and write to whatever comes after. It's rare
> enough to have files with digit-digit names that it was deemed OK to
> break the redirection rules in that special case, but it would cause
> to many problems to generalize it.
>
> } # The from_number and to_number are read in from a list of files to process
> } and injected between a filename pattern's prefix and extension.
> }
> } for file in ${SFNPAT:r}-<${from_number}-${to_number}>.${SFNPAT:e}
>
> Use the {x..y} syntax:
>
>     for file in ${SFNPAT:r}-{${from_number}..${to_number}}.${SFNPAT:e}
>
> This latter expands to the full list of names rather than globbing them,
> so it won't skip any missing files, but it will probably work in your
> example.
>
> If there may be gaps in the file sequence so you really do need to do
> the glob, put the entire expression in a variable like so:
>
>     local slice="<${from_number}-${to_number}>"
>     for file in ${SFNPAT:r}-${~slice}.${SFNPAT:e}

Variable can be avoided with the usual ${:-…} hack:

    for file in ${SFNPAT:r}-${~${:-<$from_number-$to_number>}}.${SFNPAT:e}