Pipe, when this shell command is going to executed ?

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I'm new to Perl, i have a script like this :

#!/usr/bin/perl -w
use strict;

my @word = qw(xxx yyy zzz);
open(PF,"|grep xxx") or die "failed \n";
foreach(@word) {
  print "here \n";
  print PF $_;
}
print "going to close filehandle\n";
close(PF) or die "failed\n";
print "here 2\n";
[download]

I thought i'll get 'xxx' but that's not what i've got. Then i changed print PF $_; to print PF "$_ \n"; and i got the result that i expect.

But i can't explain the real different of these 2 codes to my self.

And i need your help.

It's looks when close(PF) eq to echo xxxyyyzzz |grep xxx.

Thank you

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Re: Pipe, when this shell command is going to executed ? by Skeeve (Parson) on Sep 08, 2006 at 20:51 UTC
You don't output the words in your first version line by line but in one line. In your second you append one line-end to each line and so you get three lines. `s$$([},&%#}/&/]+}%&{});#$&&s&&$^X.($'^"%]=\&(\|?{%` `+`.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e	[reply] [d/l] [select]
Re: Pipe, when this shell command is going to executed ? by derby (Abbot) on Sep 09, 2006 at 10:50 UTC
Well the structure is a bit odd to begin with but basically grep (and most other Unix utilities) is line-oriented. So in your first version, grep sees the input as "xxxyyyzzz" and in the second one, grep sees the input as "xxx\nyyy\nzzz\n". So the first one is similar to `echo -e "xxxyyyzzz" \| grep "xxx"` and the second one is similar to `echo -e "xxx\nyyy\nzzz" \| grep "xxx"` -derby	[reply] [d/l] [select]