Passing $2 to a sub

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

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 $_;
}
[download]

The output I am getting is:

apples
    >apples
trees
    >trees
etc..
    >etc..
[download]

The expected output would be, I thought...

apples
apples
trees
trees
etc..
etc..
[download]

JAPP SparkeyG

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Re: Passing $2 to a sub by japhy (Canon) on Feb 13, 2001 at 22:53 UTC
`$_` 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	[reply]
Re: Re: Passing $2 to a sub by SparkeyG (Curate) on Feb 13, 2001 at 22:55 UTC
Ahh, boy is my face red. Thanx SparkeyG	[reply]
Re: Passing $2 to a sub by baku (Scribe) on Feb 13, 2001 at 23:03 UTC
You can't use `$_` 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 }` [download] The $x syntax only works for @x variables when followed by a subscript in []'s. See perlvars for LOTS of details :-)	[reply] [d/l] [select]
Re: Passing $2 to a sub by Gloom (Monk) on Feb 13, 2001 at 22:56 UTC
Try something like this : `if( /^\s>/ ) { print "$'\n"; createTable( $' ); } sub createTable { print shift; }` [download] Hope this helps*	[reply] [d/l]
Re: Re: Passing $2 to a sub by the_slycer (Chaplain) on Feb 13, 2001 at 23:13 UTC
I may be wrong (I've only read Mastering Regular Expressions once), but doesn't using `$&, $'`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]`	[reply] [d/l] [select]
Re: Re: Re: Passing $2 to a sub by MeowChow (Vicar) on Feb 13, 2001 at 23:28 UTC
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	[reply]