But actually I want to find the total number of lines without opening the file

Impossible. Actually, using system or backticks, you are creating a new process and opening more files than you would just using Perl.

Update: But if you insist on forking, how about

sub line_count {
   my ($fname) = @_;
   open(my $pipe, '-|', 'cat', $fname)
      or die("Unable to launch cat: $!\n");
   1 while <$pipe>;
   return $.;
}
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OK Thanks.. But i ll be really surprised if there is no way i can use the output directed to STDOUT by system command within my program.
Gaurav

"Wisdom begins in wonder" - Socrates, philosopher

huh? I've presented two ways of getting a child's output already! (qx// and open '-|')

Update: Here's a third way:

use IPC::Open2 qw( open2 );

sub line_count {
   my ($fname) = @_;
   my $pid = open2(my $fr_child, undef, 'cat', $fname) or die;
   1 while <$fr_child>;
   waitpid $pid, 0;
   return $.;
}
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You may not have noticed the

 qx//
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that ikegami's first response quoted.

That command will capture the output of any system command run. See also the "backticks" operator, which is identical to qx.

     "As you get older three things happen. The first is your memory goes, and I can't remember the other two... " - Sir Norman Wisdom

Why you think so?

my $fileName = '/some/path/to/file.ext';
my $returnVal = `wc -l $fileName`;
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I want to find the total number of lines without opening the file

If you use wc -l, it opens the file, reads through the content (counting newlines), closes the file and returns a count. Whether you do the reading in Perl, or some external program does, it still must occur.

Also, i am keen to learn how can we use the output of system command (that is directed to STDOUT) within our program

  my $file = '/path/to/file';
  my $output = `/bin/wc -l '$file'`;
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Note $file is subject to shell-escaping rules.

Alternatively, you can use the pipe form of open as ikegami has already observed.

-David

Note $file is subject to shell-escaping rules

Easily handled:

my $file = '/path/to/file';
my $output = `/bin/wc -l \Q$file\E`;
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