@_ variable of perl not working in ubuntu12.10

ravisingh1 · 07-06-2013, 10:01 PM

I use split function without assigning it to any variable. So, it should by default be assigned to @_. Now when I give command to print its elements as shown below, I get null.

Code:

print ($_[1]);

I tried all different ways to see if I get the output but to no avail. i get null only.

Keeping everyithng same and now assigning to a variable like @check, it works.

linosaurusroot · 07-08-2013, 05:24 AM

Quote:

Originally Posted by ravisingh1

I use split function without assigning it to any variable. So, it should by default be assigned to @_. Now when I give command to print its elements as shown below, I get null.

Code:

print ($_[1]);

I tried all different ways to see if I get the output but to no avail. i get null only.

Keeping everyithng same and now assigning to a variable like @check, it works.

This would be more interesting if you showed your split() command and the data you supply to it.
Also did you display the result immediately after before @_ could have been changed?

bonnydeal · 07-18-2013, 08:53 AM

Quote:

Originally Posted by ravisingh1

I use split function without assigning it to any variable. So, it should by default be assigned to @_. Now when I give command to print its elements as shown below, I get null.

Code:

print ($_[1]);

I tried all different ways to see if I get the output but to no avail. i get null only.

Keeping everyithng same and now assigning to a variable like @check, it works.

Why do you assume split assigns to @_ ?
Nowhere in the docs does it say that it will do so.

If you do not save the returned value, you will not be able to access it.

ravisingh1 · 07-18-2013, 12:22 PM

Quote:

Originally Posted by bonnydeal

Why do you assume split assigns to @_ ?
Nowhere in the docs does it say that it will do so.

If you do not save the returned value, you will not be able to access it.

This I say after reading the book: UNIX - concepts and applications by Sumitabha Das. There a few examples are also mentioned showing this.
As you say that you haven't seen in any docs, let me check internet and find out.

linosaurusroot · 07-18-2013, 01:30 PM

Quote:

perldoc -f split
split /PATTERN/,EXPR,LIMIT
split /PATTERN/,EXPR
split /PATTERN/
split Splits the string EXPR into a list of strings and
returns that list. By default, empty leading fields
are preserved, and empty trailing ones are deleted.
(If all fields are empty, they are considered to be
trailing.)

In scalar context, returns the number of fields
found and splits into the @_ array. .....

And there it is.

bonnydeal · 07-19-2013, 04:41 AM

Quote:

Originally Posted by linosaurusroot

And there it is.

Sorry,

you have different documentation to me. In my documentation there is no mention of setting @_ as a result of calling split in scalar context.

Code:

split /PATTERN/,EXPR,LIMIT
split /PATTERN/,EXPR
split /PATTERN/
split
Splits the string EXPR into a list of strings and returns the list in list context, or the size of the list in scalar context.
If only PATTERN is given, EXPR defaults to $_ .
Anything in EXPR that matches PATTERN is taken to be a separator that separates the EXPR into substrings (called "fields") that do not include the separator. Note that a separator may be longer than one character or even have no characters at all (the empty string, which is a zero-width match).
...

This is also the same in the documentation at
perldoc.perl.org.

However in your documentation it says:

in scalar context, returns the number of fields found and splits into the @_ array.
If this is correct for your version of perl, then you need to let the interpreter know you want scalar context by assigning to a scalar variable:

Code:

my $x = split /\s/, $string; 
print $_[0];    # @_ set by call to split ... ???

NB. Your documentation is different to that at perldoc.perl.org, so the above may not work. It definitely does NOT work on my system.

linosaurusroot · 07-19-2013, 05:57 AM

Code:

#!/usr/bin/perl -w

$date=`date`;

split(/\s+/, $date);

foreach (@_) {
     print  ++$n, " ", $_, "\n";
}

Quote:

$ ./split_test.plx
Use of implicit split to @_ is deprecated at ./split_test.plx line 5.
Name "main::n" used only once: possible typo at ./split_test.plx line 8.
1 Fri
2 Jul
3 19
4 11:47:58
5 BST
6 2013

version 5.008007

bonnydeal · 07-20-2013, 03:39 AM

It does not work for the OP or me.

linosaurusroot · 07-20-2013, 07:30 AM

It's been taken out of later versions of Perl. 5.014 for instance needs an array explicitly set to the split() return values.