Re: Filehandles and Input and Output Filters

devarishi:

Here's a trivial example. Suppose you have a program that generates some output, but you'd like the output sorted. You can do it like so:

use strict;
use warnings;
open my $F1, '| sort >t' or die;
while (<DATA>) {
    print $F1 $_;
}
__DATA__
the
quick
red
fox
jumped
over
the
lazy
brown
dog
[download]

This trivial program just writes a few words, and then uses the sort program to sort the output using the sort program as a filter. When you run it, you get this:

$ perl foo.pl
$ cat t
brown
dog
fox
jumped
lazy
over
quick
red
the
the
[download]

...roboticus

When your only tool is a hammer, all problems look like your thumb.

Comment on Re: Filehandles and Input and Output Filters Select or Download Code

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Re^2: Filehandles and Input and Output Filters by devarishi (Initiate) on Nov 03, 2011 at 13:35 UTC
roboticus: Thanks a lot! Based upon my understanding of your program above, I wrote this small one: `#!/usr/bin/perl -w open ($FH,'\| sort -n') or die($!); while(<ARGV>){ print $FH $_; } close $FH;` [download] Thanks again for "__DATA__" as well. There is one thing I would like mention: I used to write FH instead of $FH in open() as the file-handler. But both of them work. I did not know it. Please have a look at this: `[demo@localhost Perl]$ cat bar.pl #!/usr/bin/perl -w open (FH,'\| sort') or die($!); $count=0; while(<ARGV>){ print FH $_; print $count++ . "\n"; } close FH; [demo@localhost Perl]$ bar.pl words 0 1 2 3 4 A ABC a to z Buy Why` [download] The line numbers are being printed out first and then the sorted list of the words. That means (this is what I understand now) that the data are being fed to the "sort" command which returns its result when all the input to it is fed.	[reply] [d/l] [select]
Re^3: Filehandles and Input and Output Filters by roboticus (Chancellor) on Nov 04, 2011 at 00:51 UTC
devarishi: Yes, it sounds like you've got a handle on it, now. Note that you can also have a filter on the input, too. So if you wanted to process the records in sorted order, you could open the incoming data stream with a filter to do so. Regarding the `$FH` file handle versus the `FH` version: Modern perl practice discourages the old style (`FH`) style. The older style continues to work, obviously, but using a file handle in a scalar allows you a bit more flexibility in scoping and a bit more simplicity when passing the file handle to subroutines and such. ...roboticus When your only tool is a hammer, all problems look like your thumb.	[reply] [d/l] [select]