s /// | s () () i | / i | / g | \ U | \ u | \ L | \ l | \ U \ l | split | join | the hash matched | matched to the variable | `date` | $ ^ I

  1 #!/usr/bin/perl -w
  2 
  3 use strict;
  4 use warnings;
  5 
  6 $_='She is a good girl
  7 and  likes helping others
  8 ';
  9 
 10 s/she/he/i;print "$_";
 11 
 12 #he is a good girl
 13 #and  likes helping others
 14 
 15 s/hae/she/i;print "$_";
 16 
 17 #he is a good girl
 18 #and  likes helping others
 19 
 20 s/(he)/$1@ @/i;print;
 21 
 22 #he@ @ is a good girl
 23 #and  likes helping others
 24 
 25 s/s$/ours,/m;print;
 26 
 27 #he@ @ is a good girl
 28 #and  likes helping otherours,
 29 
 30 s/(\w*)ing/$1/g;print;
 31 
 32 #he@ @ is a good girl
 33 #and  likes help otherours,
 34 
 35 $_ ='homeN home ome ooo
 36 ';
 37 
 38 s/h/i/;print;
 39 
 40 #iomeN home ome ooo
 41 
 42 s/o/g/g;print;
 43 
 44 #igmeN hgme gme ggg
 45 
 46 s(gme)(123)g;print;
 47 
 48 #i123N h123 123 ggg
 49 
 50 s(n)(pppp)i;print;
 51 
 52 #i123pppp h123 123 ggg
 53 
 54 (my $copy = $_) =~ s/3\s/__/g;print "$copy$_";
 55 
 56 #i123pppp h12__12__ggg
 57 #i123pppp h123 123 ggg
 58 
 59 #my $copy = $_ =~ s/3\s/__/g;print "$copy$_";
 60 
 61 #i123pppp h123 123 ggg
 62 #2i123pppp h12__12__ggg
 63 
 64 s/(\w*)/\U$1/gi;print;
 65 
 66 #I123PPPP H123 123 GGG
 67 
 68 s/(\w*)\s(\w*)/\l$1/i;print;
 69 
 70 #i123PPPP 123 GGG
 71 
 72 s/(GGG)/\u\L$1/gi;print;
 73 
 74 #i123PPPP 123 spGgg
 75 
 76 print "\u\Lmy name is \Uyy\n";
 77 
 78 #My name is YY
 79 
 80 my @split = split / /,$_;print "@split";
 81 
 82 #i123PPPP 123 Ggg
 83 
 84 my @new_split = split;print"@new_split\n";
 85 
 86 #123PPPP 123 Ggg
 87 
 88 my @new_split1 = split /\s/;print"@new_split1\n";
 89 
 90 #123PPPP 123 Ggg
 91 
 92 my $glue = 'xxx';my $string = join $glue,@new_split;print "$string\n";
 93 
 94 #i123PPPPxxx123xxxGgg
 95 
 96 $_ = 'aaa bb ddd';
 97 my ($next1,$next2,$next3) = /(\S+) (\S+) (\S+)/;print "$next2\n";
 98 
 99 #bb
100 
101 my %hash = ($string =~ /([A-Z]+)([0-9]+)/gi);
102 
103 foreach my $key(keys %hash)
104 {
105     print "$key and $hash{$key}\n";
106 }
107 
108 #PPPPxxx and 123
109 #i and 123
110 
111 $_ = "a\nmmmmmmm\nabc\n\s\s\ssdsfs\n";
112 print "$1\n" if /(.*c$)/gm;
113 
114 #abc
115 
116 my $time = `date`;print "$time";
117 
118 #Sun Jun 23 21:34:46 HKT 2019
119 
120 $^I = ".bak";
121 
122 my $input = <>;

Questions:  1 CAT 1 .txt | perl test.pl  after no backup file 1.txt.bak?