Regular expression help

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

Replies are listed 'Best First'.
Re: Regular expression help by ChOas (Curate) on Oct 23, 2008 at 07:02 UTC
You mean literally ? `print "'$&'\n" while ($string=~/\bRequired\b/g);` [download] GreetZ!, ChOas print "profeth still\n" if /bird\|devil/;	[reply] [d/l]
Re: Regular expression help by johngg (Canon) on Oct 23, 2008 at 10:15 UTC
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;` [download] The output. `This bat the other that` [download] I hope this is useful. Cheers, JohnGG	[reply] [d/l] [select]
Re: Regular expression help by brsaravan (Scribe) on Oct 23, 2008 at 05:29 UTC
$& - 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;` [download]	[reply] [d/l]
Re^2: Regular expression help by JavaFan (Canon) on Oct 23, 2008 at 11:12 UTC
Some questions regarding your solution. Why the /g modifier considering that you're matching (in scalar context) against $_ only once before $_ changes? Why a regexp anyway? Considering that "Required" is a fixed string, and you anchor it on both ends, `$_ eq "Required"` will do as well. Why quotes around $&?	[reply]
Re: Regular expression help by Anonymous Monk on Oct 23, 2008 at 06:12 UTC
How can i use regular expression to get only required fields and then print using $& ? Why are you focusing on $&?	[reply]
Re: Regx help by ikegami (Patriarch) on Oct 23, 2008 at 04:15 UTC
`print("$_\n") for ( split(/ /, $string) )[0,3];` [download] I have no idea what `$&` has to do with anything. Or regular expressions, really, but I did end up using one.	[reply] [d/l] [select]
Re: Regular expression help by moritz (Cardinal) on Oct 23, 2008 at 07:13 UTC
`my $result = join ' ', (split m/ /, $string)[0, 3];` [download]	[reply] [d/l]
Re: Regular expression help by JavaFan (Canon) on Oct 23, 2008 at 09:56 UTC
`say $& while $string =~ /\bRequired\b/g;` [download]	[reply] [d/l]
Re: Regular expression help by Wiggins (Hermit) on Oct 23, 2008 at 17:24 UTC
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....	[reply]
Re: Regx help by Punitha (Priest) on Oct 23, 2008 at 04:22 UTC
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 }` [download] Punitha	[reply] [d/l]