Regular expression help

[ashnator]

Dear Monks,

$string = "Required Not_Required Not_Required Required";

How can i use regular expression to get only required fields and then print using $& ?

[ChOas]

You mean literally ?



print "'$&'\n" while ($string=~/\bRequired\b/g);

[johngg]

You can use capturing parentheses and a global match. Avoid using $&, $` and $' if you can as once used in a script they impose a performance penalty on all regular expressions in that script.

#!/usr/bin/perl -l
#
use strict;
use warnings;

my @required = (
   q{this},
   q{that},
   q{the other},
   q{bat},
   );

my $rxRequired = do
   {
       local $" = q{|};
       qr{(?i)\b(@required)\b};
   };

my $text =
   q{This afternoon I found a bat in the other bath, that was odd!};

print for $text =~ m{$rxRequired}g;

The output.

This
bat
the other
that

I hope this is useful.

Cheers,

JohnGG

[ikegami]

print("$_\n") for ( split(/ /, $string) )[0,3];

I have no idea what $& has to do with anything. Or regular expressions, really, but I did end up using one.

[brsaravan]

$& - Contains the string matched by the last pattern match.

use strict;

my $string = "Required Not_Required Not_Required Required";
my @words = split(" ",$string);
map {$_ =~ /^Required$/g;print "$&"}@words;

[JavaFan]

Some questions regarding your solution.
1. Why the /g modifier considering that you're matching (in scalar context) against $_ only once before $_ changes?
2. Why a regexp anyway? Considering that "Required" is a fixed string, and you anchor it on both ends, $_ eq "Required" will do as well.
3. Why quotes around $&?

[Anonymous Monk]

How can i use regular expression to get only required fields and then print using $& ?
Why are you focusing on $&?

[JavaFan]

say $& while $string =~ /\bRequired\b/g;

[moritz]

my $result = join ' ', (split m/ /, $string)[0, 3];

[Wiggins]

I think there is a communications fault here. Does the phrase "only required fields" in the question mean fields whose content is the string "required" (which would be none); or is the question about how to extract only the first and last, space separated tokens from a string.

Is the $string in the question literal, or simply showing the position of "required fields"?

Clarification please....

[Punitha]

Hi

Please take a note about the regular expressions here http://perldoc.perl.org/perlretut.html and do you want something like this?

use strict;
my $string = "Required Not_Required Not_Required Required";
while($string=~/\bRequired\b/gi){
    print "$&\n";##Here it will print only required text with non word
+ character before and after
}

Punitha