Perl: Reading from file and saving into an array

Question

I had got a script in Perl and my task is to do some changes in it. This of course means to understand which part does exactly what. I am not familiar with Perl language but I tried to read through some tutorials, but still some things are confusing me. And I got stuck in following part:

while (<KOEFICIENTYfile>) {
    @_=(split(/\s+/, $_));
    push(@ZAID,shift(@_));
    $KOEFICIENTY{$ZAID[-1]}=[@_];
}

As I understands this part then it:

Reads line from filehandle KOEFICIENTYfile
Separates them by spaces (one or more)
Loads first item from this separated array into array ZAID (and in the process, removes it from @_)
??? Adds a rest of a separated array into array KOEFICIENTY? I am confused by curly brackets part and by square brackets after equals sign.

I think that I understood the meaning of @, $, @_ or negative indexing but this is beyond me. Can you please advice me on meaning of this?

All suggested answers was helpful and each had some interesting point in it, but as accepted answer i chosen @Disco 3´s answer since it was descriptive, helpful and suggested Data:Dumper. Anyway, thank you all. — Rao
– Rao, Commented Oct 12, 2015 at 9:43

matt freake · Accepted Answer · 2015-10-12 09:33:44Z

1

[-1] indexing is just a shortcut way to say "last element of the array".

KOEFICIENTY is actually a hash (you can tell this because it is using curly braces, instead of square ones, around the index), so you're putting the rest of the array @_ into a hash called KOEFICIENTY with a key of the last element of the array.

If you include:

use Data::Dumper

at the top of the script and do

print Dumper(%KOEFICIENTY)

it will nicely format the output for you, which may help

edited Oct 12, 2015 at 9:33

answered Oct 12, 2015 at 9:00

matt freake

5,1284 gold badges29 silver badges60 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Alnitak · Accepted Answer · 2015-10-12 09:16:22Z

1

The original coder was trying to be too clever using the negative offset. It would have been much more obvious if the code had been written with a simple temporary variable thus:

while (<KOEFICIENTYfile>) {
    @_ = (split(/\s+/, $_));
    my $key = shift(@_);
    push(@ZAID, $key);
    $KOEFICIENTY{$key} = [@_];
}

The braces on $KOEFICIENTY show that this is a "hash" of key/value pairs named %KOEFICIENTY, and not a normal array.

If you don't actually need to preserve the sort order of the keys you could just use keys %KOEFICIENTY to retrieve them instead of storing them in @ZAID.

edited Oct 12, 2015 at 9:16

answered Oct 12, 2015 at 9:04

Alnitak

341k72 gold badges420 silver badges503 bronze badges

1 Comment

Arc676 Over a year ago

So what are the braces? ({...})

syck · Accepted Answer · 2015-10-12 08:59:30Z

0

@zaid is a list, into which the first part of the split is added.

%KOEFICIENTY is a hash, in which a reference to the rest of the split is stored as a list reference under the key of the first part.

So if the line is a b c, @zaid will get a and %KOEFICIENTY{'a'} will hold a reference to a list containing b and c.

answered Oct 12, 2015 at 8:59

syck

3,0391 gold badge15 silver badges25 bronze badges

Collectives™ on Stack Overflow

Perl: Reading from file and saving into an array

3 Answers 3

Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related