/^/m|/$/m|\b|\B|$&|$`|$'|变量捕获|()?|(?:pattern)|(?<LABEL>PATTERN)|$+{LABEL}|(|)|\g{LABEL}

 #!/usr/bin/perl

 use strict;
 use warnings;

 $_='

  $$   oinn     &&&
 ninq   kdownc
 aninp
     kkkk';

 if (/(.*)k\Z/){print "$1\n";}else{print "no match\n";}

 #   kkk

 if (/^n(.*)/m){print "$1\n";}else{print "no match\n";}

 #inq   kdownc

 if (/(.*\bn.n\b.*)/){print "$1\n";}else{print "no match\n";}

 #no match

 if (/.*(\Bn.n\B).*/){print "$& and $1\n";}else{print "no match\n";}

 #aninp and nin

 if (/\w*(i)\w*/){print "$& and $1 and $` and $'\n";}else{print "no match\n";}

 #oinn and i and
 #
 # $$    and      &&&

 my $new_words =
 'sewfbiurev214`7i074o//m,m]\[g
 sw  d
        trp';

 if ($new_words =~ /(.*)g$/m){print "$1\n";}else{print "no match\n";}

 #sewfbiurev214`7i074o//m,m]\[

 my $test = (<> =~ /^sd(.*)/m );if ($test){print "right!,it is $1\n";}else{print "no match\n";}

 #sdkkk
 #right!,it is kkk

 my $what = shift @ARGV;if ($new_words =~ /(.*)($what$)/m){print "right!,it is $1 and $2\n";}else{print "no match\n";}

 # perl test.pl g
 # right!,it is sewfbiurev214`7i074o//m,m]\[ and g

 $new_words =~ /(.*)g$/m;$new_words =~ /(.*)s$/m;print "$1\n";

 #sewfbiurev214`7i074o//m,m]\[

 $new_words =~ /(.*q)?(.*)g$/m;print "$2\n";

 #sewfbiurev214`7i074o//m,m]\[

 $new_words =~ /(?:.*q)?(.*)g$/m;print "$1\n";

 #sewfbiurev214`7i074o//m,m]\[

 $new_words =~ /(?:.*q)?(|s)(.*)g$/m;print "$1 and $2\n";

 #s and ewfbiurev214`7i074o//m,m]\[

 $new_words =~ /(?:.*q)?(?:|s)(?<label>.*)g$/m;print "$+{label}\n";

 #ewfbiurev214`7i074o//m,m]\[

 $new_words =~ /(?:.*q)?(?<label2>(|s))(?<label>.*)g$/m;print "$+{label} and $+{label2}\n";

 #ewfbiurev214`7i074o//m,m]\[ and s

 my $test2 = 'aavvbbssd';
 $test2 =~ /^(?<word1>.)\g{word1}(?<word2>.)\g{word2}/m;print "$+{word2} and $+{word1}\n";

 #v and a

 print "|$`<$&>$'|\n";

 #|<aavv>bbssd|