help in opening file with pipe

[uva]

hello monks, what the difference between opening the file with pipe sysmbol and without pipe.where we actually use i mean which one is more efficient in which place and where it is inefficeient. eg:

open(handle,"d:/help.txt |"); and 
open(handle,"d:/help.txt");

[zentara]

When you open the file without the pipe, you are opening it for editing or reading it. When you open it with a pipe, you are doing IPC (see perldoc perlipc ). It means that you are "executing the script". You can put the pipe at the front or the end of the open string. If the pipe is at the front, it means that you can write to the filehandle, and it will be sent to the programs STDIN. If the pipe is at the end of the open string, it means you can read the filehandle, which will contain the STDOUT output of the executed program. It you want to setup a program to execute, where you can manipulate BOTH the STDIN and STDERR, use IPC::Open2 (or IPC::Open3 to include STDERR).

[svenXY]

Hi,
you would only use the pipe if there was some command that produces some output that you want to catch (e.g. open(CMD, 'ls -l |')). If you only want to open a file for reading, you shouldn't use the pipe operator. See open for details.
Regards,
svenXY

[uva]

it means we get the output from the command and we use that output as a filename.right

[blazar]

(Incidentally: s/$/?/)

No, it's not right. It means that a process is forked for that command and that the output of that command, i.e. what that it will inject into STDOUT is returned to you when you read from the opened filehandle, as if it were the content of an actual file.

[zentara]

#!/usr/bin/perl

my $pid = $$;

open (T,"top -d 1 -p $pid b |" ) or die $!;
$|=1;
while(<T>){
  $output = $_;
  $output =~ tr/\n//;
#print $output; 

  my @words=split(/\s+/,$output);
print join "\n",@words,"**************\n";

#  if($words[0] =~ /$pid/){print "$words[4]\n"} 
}

[zentara]

For windows users check out ActiveStates perlipc

Here is a super-simple piped input, using a perl script.

#the Main script to run

#!/usr/bin/perl -w
$|++;
open( H, " | other_script") or die "$!\n";
print H "hi\n";
sleep 1; #let other script print before dieing  
__END__
#####################################
#the other_script

#!/usr/bin/perl
$|++;
my $in = <>;
print "$in\n"
__END__

[mickeyn]

You're missing 'cat' before the file name (or 'type' if you're running on Windows).

open(handle,"type d:/help.txt |");

The pipe as you wrote it doesn't get anything in its STDIN.

Enjoy,
Mickey