Re^2: Filehandles and Input and Output Filters

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;
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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
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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.

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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]

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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.

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