Hash becomes uninitalized without warning... with warning

sendrahiok has asked for the wisdom of the Perl Monks concerning the following question:

I was making great progress with my first attempt using Perl but have come across an uninitialized value problem.

I've distilled the issue down to the following code. I define a hash with 1 pair, ask the user to input a number. Then the hash is undef.

I'm using a fresh strawberry install and run it from the cmd line in Win 7 using 'perl filename.pl'

#! /usr/bin/perl
use feature ':5.10';
use strict;
use warnings;

#define a hash
my %p = ("1","Rekjavik");

#check it's there (returns "Rekjavik")
say $p{1};

#ask for input from user (user inputs the number 1)
my $t = <>;

#the hash has disappeared! (returns undef)
say $p{$t};
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Comment on Hash becomes uninitalized without warning... with warning Download Code

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Re: Hash becomes uninitalized without warning... with warning by wind (Priest) on Apr 13, 2011 at 21:32 UTC
chomp your input: `my $t = <>; chomp $t;` [download] or `chomp(my $t = <>);` [download]	[reply] [d/l] [select]
Re^2: Hash becomes uninitalized without warning... with warning by sendrahiok (Initiate) on Apr 13, 2011 at 21:42 UTC
That's fantastic. My hat goes off to you. Thanks for the help.	[reply]
Re: Hash becomes uninitalized without warning... with warning by ww (Archbishop) on Apr 13, 2011 at 22:07 UTC
No, the hash hasn't disappeared. As wind's reply shows, if the input, `$t` is 1, you'll get Rekjavik back... but consider what happens if the input is "2," "3" or "42." `say $p{$t};` is the same thing as `say $p{1};` when the input is "1" but if you wish to extend your hash with a new key-value pair you'll have to add instructions to do so.	[reply] [d/l] [select]
Re^2: Hash becomes uninitalized without warning... with warning by perl-diddler (Chaplain) on Apr 14, 2011 at 02:16 UTC
I think he was wondering why, when input a value of "1", at the terminal, it wasn't matching his data value. I don't think he was trying to handle cases asking for the answer of everything -- just trying to get a basic understanding of why his test case wasn't working, in what would seem to many new perl programmers, to be such a simple case! And who among us haven't been bitten by that simple newline more than once! :-)	[reply]
Re: Hash becomes uninitalized without warning... with warning by Anonymous Monk on Apr 14, 2011 at 15:50 UTC
A beautiful first post, with actual thought put into the problem and question! Maybe the human race isn't doomed after all :)	[reply]