Shell Programming and Scripting

#!/usr/bin/perl
 
 
my @src=`ls /home/t1/`;
my @dest=`ls /home/t2/`;
 
foreach my $file (@src){
   @match=grep(/$file/, @dest);
   if (@match==0){
      print "Found $file";
   }else{
      print "Not found $file";
   }
}

Found def.txt
Not found $ABC.TXT

#!/usr/bin/perl
 
 
my @src=`ls /home/t1/`;
my @dest=`ls /home/t2/`;
 
SRC: foreach my $src (@src){
   DEST: foreach my $dest (@dest) {
        if ( $src eq $dest ){
          print "Found $file";
          next SRC;
       }
   }
   print "Not found $src";
}

$ cat script.pl
use strict;
use warnings;

my %src = ();
my %dest = ();
map { $src{$_} = 1 } qx{ ls -1 /home/t1 };
map { $dest{$_} = 1 } qx{ ls -1 /home/t2 };

map { print "Found $_"; delete $src{$_} } grep { $dest{$_} } keys %src;
for (keys %src) {
        print "Not found $_";
}
$ perl script.pl
(...output suppressed...)

$
$
$ cat -n cmpdir.pl
  1  #!perl
  2  use Benchmark qw (cmpthese);
  3
  4  my @src  = `ls -1 ./t1/`;
  5  my @dest = `ls -1 ./t2/`;
  6
  7  sub using_grep {
  8    my $found = 0;
  9    my $notfound = 0;
 10    foreach my $file (@src){
 11       @match = grep {/$file/} @dest;
 12       if ($#match == -1){
 13         $notfound++;
 14       } else {
 15         $found++;
 16       }
 17    }
 18    return "$found, $notfound";
 19  }
 20
 21  sub using_loop {
 22    my $found = 0;
 23    my $notfound = 0;
 24    SRC: foreach my $src (@src) {
 25      DEST: foreach my $dest (@dest) {
 26        if ( $src eq $dest ) {
 27          $found++;
 28          next SRC;
 29        }
 30      }
 31      $notfound++;
 32    }
 33    return "$found, $notfound";
 34  }
 35
 36  print "From using_grep, (found, notfound) = ", using_grep(), "\n";
 37  print "From using_loop, (found, notfound) = ", using_loop(), "\n\n";
 38
 39  cmpthese (2, {
 40      using_grep => sub {using_grep()},
 41      using_loop => sub {using_loop()},
 42    }
 43  );
 44
$
$
$ perl cmpdir.pl
From using_grep, (found, notfound) = 10005, 0
From using_loop, (found, notfound) = 10005, 0
 
        s/iter using_grep using_loop
using_grep    148         --       -95%
using_loop   7.27      1943%         --
$
$

$
$ # Elements $C, $$D, $$$E of array @x exist in array @y, but
$ # that is not reported because Perl tries to interpolate
$ # the "$" regex metacharacter.
$
$ perl -le '@x = qw(    B   $C   $$D  $$$E    F );
            @y = qw( A  B   $C   $$D  $$$E      );
            foreach $i (@x) {
              $exists = grep {/$i/} @y;
              printf("%-10s %-20s in \@y\n", $i, $exists==1 ? "exists" : "does not exist");
            }'
B          exists               in @y
$C         does not exist       in @y
$$D        does not exist       in @y
$$$E       does not exist       in @y
F          does not exist       in @y
$
$
$ # Works fine with quotemeta function
$
$ perl -le '@x = qw(    B   $C   $$D  $$$E    F );
            @y = qw( A  B   $C   $$D  $$$E      );
            foreach $i (@x) {
              $exists = grep {/\Q$i\E/} @y;
              printf("%-10s %-20s in \@y\n", $i, $exists==1 ? "exists" : "does not exist");
            }'
B          exists               in @y
$C         exists               in @y
$$D        exists               in @y
$$$E       exists               in @y
F          does not exist       in @y
$
$