Passing $2 to a sub

[SparkeyG]

In the following snippit, I wish to take the second match, $2, and pass it to a sub that will create a DB table. The problem is that w/in the sub, the variable shows the entire line matched.

if ( /(^\s?>)(.*)$/ ) { 
    print "$2\n";
    &createTable($2);
    next;
}

sub createTable {
    print $_;
}

The output I am getting is:

apples
    >apples
trees
    >trees
etc..
    >etc..

The expected output would be, I thought...

apples
apples
trees
trees
etc..
etc..

JAPP SparkeyG

[japhy]

$_ is not the argument passed the function. To get that, you need to access the @_ array -- you want the first element, which is $_[0].

japhy -- Perl and Regex Hacker

[SparkeyG]

Ahh, boy is my face red.
Thanx
SparkeyG

[Gloom]

Try something like this :



if( /^\s*>/ ) {
    
    print "$'\n";
    createTable( $' );
    
}

sub createTable {
    print shift;
}


Hope this helps

[the_slycer]

I may be wrong (I've only read Mastering Regular Expressions once), but doesn't using $&, $'or $` anywhere in your program cause some fairly severe performance issues?

Looks like the regex originally used should work - just trying to print $_ instead of $_[0]

[MeowChow]

Yep, you are right. From perlre:

WARNING: Once Perl sees that you need one of $&, $`, or $' anywhere in the program, it has to provide them for every pattern match. This may substantially slow your program. Perl uses the same mechanism to produce $1, $2, etc, so you also pay a price for each pattern that contains capturing parentheses. (To avoid this cost while retaining the grouping behaviour, use the extended regular expression (?: ... ) instead.) But if you never use $&, $` or $', then patterns without capturing parentheses will not be penalized. So avoid $&, $', and $` if you can, but if you can't (and some algorithms really appreciate them), once you've used them once, use them at will, because you've already paid the price. As of 5.005, $& is not so costly as the other two.

   MeowChow                                   
               s aamecha.s a..a\u$&owag.print

[baku]

You can't use $_ in stead of @_ like that. You want to change the subroutine to one of:

sub createTable
{
  my $value = shift;
  print $value;
}

# or

sub createTable
{
  print $_[0]; # subscript means array
}

The $x syntax only works for @x variables when followed by a subscript in []'s. See perlvars for LOTS of details :-)