Re^2: new to perl, syntax question

suppose you have @a= qw(1 2 3 4);
you are writting print "\n @a"; this will print 1 2 3 4.
if you are trying to write like...
$p= @a, then it will give you count of array i.e. 4
so it does not mean that if we write @a as index inside array would give the value of 4th index of array. Basically if we write code..
$b[@a] with return nothing because bare @a return complete set of value which is not a valid index and that is passing as index in @b so of course will return blank.

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Re^3: new to perl, syntax question by Marshall (Canon) on Feb 20, 2012 at 12:52 UTC
Perl syntax can be tricky. Does this help? Or just further confuse? Update: I guess it confused one Monk, because I got a down vote. I am genuinely trying to be helpful here. When you write: `$y[@x]`, you are accessing a single element of @y with the index of the scalar value of @x. Note: using $a and $b or @a or @b is in general not a good idea as the $a and $b variables have special meaning to Perl and are used in sort. Better is to use: x,y,z. However: "@a return complete set of value" this is not correct. What @a would mean is context specific. #!/usr/bin/perl -w use strict; use Data::Dumper; my @x= qw(1 2 3 4); my @y= qw(7 8 9 10 11 12 13 14); my $num = $y[@x]; # @x evaluates here to the number "4"!!! # the number of elements in @x # As said before this is a VERY unusual # formulation!!! # It looks weird because it is weird. # As mentioned above more normal would be # $y[@x-1] or $y[$#x] # I'm not saying that $y[@x] cannot have a defined, # value but just that it is "strange" absent other # context and would be worthy of a comment in the # code. print "The number in y is: $num\n"; #the 5th thing in @y!! WHOA! #print $x[@y]; # ERROR: Use of uninitialized value in print # this is because: $x[8] is undefined! # However consider this: # here [@x] means something completely different push @y, [@x]; # this means: assign new memory, # copy @x into that new memory , # push a reference to that memory # onto @y print Dumper \@y; __END__ The number in y is: 11 ### the 5th thing in @y $VAR1 = [ '7', '8', '9', '10', '11', '12', '13', '14', [ '1', '2', '3', '4' ] ]; [download]	[reply] [d/l] [select]

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Re^3: new to perl, syntax question
by Marshall (Canon) on Feb 20, 2012 at 12:52 UTC

Update: I guess it confused one Monk, because I got a down vote.
I am genuinely trying to be helpful here.
When you write: $y[@x], you are accessing a single element of @y with the index of the scalar value of @x.

Note: using $a and $b or @a or @b is in general not a good idea as the $a and $b variables have special meaning to Perl and are used in sort. Better is to use: x,y,z.

However: "@a return complete set of value" this is not correct. What @a would mean is context specific.

#!/usr/bin/perl -w
use strict;
use Data::Dumper;

my @x= qw(1 2 3 4);
my @y= qw(7 8 9 10 11 12 13 14);

my $num = $y[@x];  # @x evaluates here to the number "4"!!!
                   # the number of elements in @x
                   # As said before this is a VERY unusual 
                   # formulation!!!
                   # It looks weird because it is weird.
                   # As mentioned above more normal would be
                   # $y[@x-1] or $y[$#x]
                   # I'm not saying that $y[@x] cannot have a defined,
                   # value but just that it is "strange" absent other
                   # context and would be worthy of a comment in the
                   # code.

print "The number in y is: $num\n";  #the 5th thing in @y!! WHOA!

#print $x[@y]; # ERROR: Use of uninitialized value in print
               # this is because: $x[8] is undefined!

# However consider this:
# here [@x] means something completely different

push @y, [@x]; # this means: assign new memory,
               # copy @x into that new memory ,
               # push a reference to that memory 
               # onto @y
               
print Dumper \@y;

__END__

The number in y is: 11  ### the 5th thing in @y
$VAR1 = [
          '7',
          '8',
          '9',
          '10',
          '11',
          '12',
          '13',
          '14',
          [
            '1',
            '2',
            '3',
            '4'
          ]
        ];
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