Date: Mon, 12 Nov 2001 17:15:38 -0800 From: "Christopher R. Maden" <crism@maden.org> To: Chris Aitken <chris@ideal.net.au>, freebsd-questions@FreeBSD.ORG Subject: Re: Perl on FreeBSD Message-ID: <5.1.0.14.0.20011112171053.00a63d90@mail.maden.org> In-Reply-To: <20011113005355.GA36434@mercury.itworks.com.au> References: <5.1.0.14.2.20011113111839.03949520@mail.ideal.net.au> <5.1.0.14.2.20011113111839.03949520@mail.ideal.net.au>
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At 16:53 12-11-2001, Gavin Cameron wrote:
>On Tue, Nov 13, 2001 at 11:19:47AM +1100, Chris Aitken wrote:
> > What I want to be able to do is take the output of a FreeBSD command, and
> > pipe the output to a perl script so I can use that data....
> >
> > For example. If I ran the following at command line,
> >
> > # echo "Blah Blah Blah" | perlscript.pl
>
>#!/usr/bin/perl -w
>
>while (<>)
>{
> print;
>}
>
>Transfers standard input to standard output. Replace print inside the while
>loop to do whatever you want. The line read in is stored in $_ in this
>example.
Unfortunately, this is the obfuscated Perl way, and may not demonstrate
clearly to Chris what's going on.
First, when you pipe data into another process like that, the process sees
the data on standard input, or STDIN.
Perl uses the <fh> operator to read one line from a filehandle fh. STDIN is
one predefined filehandle, so you can use <STDIN> to read one line from
STDIN. STDIN is also the default, so Perl hackers like to just say <>
because it's easier to type. It is not always easier for someone else to read.
The while loop will keep running until its argument is false. The <fh>
operator returns false when there is nothing left to read, so while (
<STDIN> ) { ... } will execute the block until all of the input has been
consumed.
As Gavin notes, the <fh> operator assigns the line read to the $_ built-in
variable. You can print that explicitly with print $_;, or you can use
Gavin's shortcut, which is that print always prints $_ unless told
otherwise. So a more verbose version of Gavin's script is
#!/usr/bin/perl -w
use strict; # always use strict
while ( <STDIN> ) # Read one line at a time from input or console.
{
print $_; # Print the line that was read to stdout.
}
HTH,
Chris
- --
Christopher R. Maden, Principal Consultant, HMM Consulting Int'l, Inc.
DTDs/schemas - conversion - ebooks - publishing - Web - B2B - training
<URL: http://www.hmmci.com/ > <URL: http://crism.maden.org/consulting/ >
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