s///|s()()i|/i|/g|U|u|L|l|Ul|split|join|匹配到hash|匹配到变量|`date`|$^I

#!/usr/bin/perl -w

use strict;
use warnings;

$_='She is a good girl
and  likes helping others
';

s/she/he/i;print "$_";

#he is a good girl
#and  likes helping others

s/hae/she/i;print "$_";

#he is a good girl
#and  likes helping others

s/(he)/$1@ @/i;print;

#he@ @ is a good girl
#and  likes helping others

s/s$/ours,/m;print;

#he@ @ is a good girl
#and  likes helping otherours,

s/(w*)ing/$1/g;print;

#he@ @ is a good girl
#and  likes help otherours,

$_ ='homeN home ome ooo
';

s/h/i/;print;

#iomeN home ome ooo

s/o/g/g;print;

#igmeN hgme gme ggg

s(gme)(123)g;print;

#i123N h123 123 ggg

s(n)(pppp)i;print;

#i123pppp h123 123 ggg

(my $copy = $_) =~ s/3s/__/g;print "$copy$_";

#i123pppp h12__12__ggg
#i123pppp h123 123 ggg

#my $copy = $_ =~ s/3s/__/g;print "$copy$_";

#i123pppp h123 123 ggg
#2i123pppp h12__12__ggg

s/(w*)/U$1/gi;print;

#I123PPPP H123 123 GGG

s/(w*)s(w*)/l$1/i;print;

#i123PPPP 123 GGG

s/(GGG)/uL$1/gi;print;

#i123PPPP 123 spGgg

print "uLmy name is Uyy
";

#My name is YY

my @split = split / /,$_;print "@split";

#i123PPPP 123 Ggg

my @new_split = split;print"@new_split
";

#123PPPP 123 Ggg

my @new_split1 = split /s/;print"@new_split1
";

#123PPPP 123 Ggg

my $glue = 'xxx';my $string = join $glue,@new_split;print "$string
";

#i123PPPPxxx123xxxGgg

$_ = 'aaa bb ddd';
my ($next1,$next2,$next3) = /(S+) (S+) (S+)/;print "$next2
";

#bb

my %hash = ($string =~ /([A-Z]+)([0-9]+)/gi);

foreach my $key(keys %hash)
{
    print "$key and $hash{$key}
";
}

#PPPPxxx and 123
#i and 123

$_ = "a
mmmmmmm
abc
ssssdsfs
";
print "$1
" if /(.*c$)/gm;

#abc

my $time = `date`;print "$time";

#Sun Jun 23 21:34:46 HKT 2019

$^I = ".bak";

my $input = <>;

问题： cat 1.txt |perl test.pl 后并无备份文件1.txt.bak？