#!/usr/bin/env perl
use Modern::Perl;

my $line = '>foo# bar';
if( $line =~ /^>(\w+)\s(.+)$/ ){
    say "Found word $1";
} else {
    say "No match.";
}

##</code><code>##

$line =~ /^>(\w+)/;   # capture as many consecutive \w characters as possible following >
$line =~ /^>(\S+)/;  # capture as many consecutive non-whitespace chars as possible following >