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command line slice argument

ryantkoehler
Novice

Feb 28, 2012, 1:19 PM

Post #1 of 5 (1714 views)

command line slice argument	Can't Post

Hi

I would like to accept a slice argument (string) from the command line that then may be used to select a subset of columns from an input file. Doing this directly apparently does not work (error is that argument (to slice) is not numeric).

Here are some more details.

I use GetOptions to accept a command line string such as 1..5,10..15 (i.e. $col_slice = "1..5,10..15). Next, once I've got a list of items (e.g. words on a line), I would like to simply get the subset (if specified):

if ( $col_slice ) {
@words = $words[$col_slice];
}

I'm sure this is "easy" if you know the trick. I don't know the trick.

Thanks in advance for any help.
-Ryan

BillKSmith
Veteran

Feb 28, 2012, 2:44 PM

Post #2 of 5 (1711 views)

Re: [ryantkoehler] command line slice argument [In reply to]	Can't Post

Code

use strict; 
use warnings; 
my @words = qw( a b c d e f g h i j k l m n o p q ); 
my $col_slice = '1..5,10..15'; 
@words = @words[(eval $col_slice)]; 
print join( "\n", @words);

Good Luck,
Bill

ryantkoehler
Novice

Feb 28, 2012, 3:13 PM

Post #3 of 5 (1708 views)

Re: [BillKSmith] command line slice argument [In reply to]	Can't Post

Thanks for getting back to me

Unfortunately, that didn't work.

What I want is to be able to accept a string and (somehow) convert this into a slice argument (without parsing the thing myself). Your eval didn't do this.

My "first language" is C, so I was hoping there was something equivalent to printing a format string (e.g. for printf() ) that might do the conversion for me (I wasn't thinking error checking to make sure the slice syntax was reasonable.. but maybe?). I still think that Perl likely has a means to do what I'm hoping for.

Thanks again,
-Ryan

p.s. I'm uploading my script (that doesn't work with the "-csl 1..5,10..15" argument)

BillKSmith
Veteran

Feb 28, 2012, 7:23 PM

Post #4 of 5 (1702 views)

Re: [ryantkoehler] command line slice argument [In reply to]	Can't Post

It seems that your upload did not work.

I posted a complete working program. If yours does not work the same, there are only two possibilities.

You are not using GetOptions correctly. Try printing the value of $col_slice to verify that it contains the string which I used. (This is what you expect is it not?)

You are not using eval correctly. (The apparently extraneous parentheses are needed to force list context)

Good Luck,
Bill

ryantkoehler
Novice

Feb 28, 2012, 7:50 PM

Post #5 of 5 (1695 views)

Re: [BillKSmith] command line slice argument [In reply to]	Can't Post

I may be incorrect in either/both cases you mentioned. Hopefully this time the atechment works.
Thanks again for the help.

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