(perl)- trying to read from file that keep geting input in parallel- help!

sagik · 02-28-2009, 03:04 AM

hey guys,
iv'e been trying for several hours to do a little programm :

Code:

 
$file = $ARGV[0];
open FILE, $file;
while (1)
{
 @array=@array.<FILE>;       #add the lines to array from the file.
 print @array;               #prints it.
}

explanetion :
i have a device that functions like a button , and i've found that if u read the /dev/input/event5 with xxd, i can see that the same values changes when i press the button or moving it clockwise...

my problem is - how to read from this file, and how to get that several values into var's ?

thanks !

sagi.

Telemachos · 02-28-2009, 06:05 AM

What you have up there isn't Perl code. It looks (sort of?) like Ruby or I-don't-know-what. Perl doesn't use the @array.<FILE> syntax.

Here's how to get items from a file into an array:

Code:

#!/usr/bin/env perl
use strict;
use warnings;

my $file = $ARGV[0];

open my $file_handle, '<', $file
  or die "Can't open $file for reading: $!";

my @lines;

while (<$file_handle>) {
  push @lines, $_;
}

print @lines;

sagik · 02-28-2009, 07:16 AM

it's perl ... the "@array.<FILE>" thing is for the lines of the file will be added to the array (using the dot thing in the middle).

thanks anyway!,
one more question, the output that written into the file that i'm reading, is in binary... i red it using xxd. so, how can i split the HEX values and take just the values that i want? cause in this case is just like one line of string and not seperate values.

Ex. of output:
i want to get the bold values to var'!

Code:

0000000:  0807 0308 0701 0807 0008 0100 2800 0fff ..........{...
0000010:  0807 0308 0701 0807 0038 0100 2804 00ff ..............
0000020:  0807 0308 0701 0807 0208 0100 2800 0f1f ..............

Su-Shee · 02-28-2009, 07:57 AM

Use a regex if you want the hex stuff treated as something string-like or use pack/unpack.

Und read this for all the details on slurping "stuff" from files into "something" in Perl.

http://www.perl.com/pub/a/2003/11/21/slurp.html

With smaller files, I prefer the two birds with one stone method:

Code:

sub read_my_file {
    my $filetoread = shift;
    my $filehandle;
    my @filelinebyline;
    my $fileallatonce;

    open($filehandle, "<$filetoread") or die "Can't read $filetoread: $!\n";
    
    if(wantarray) {
        @filelinebyline = <$filehandle>;
    } else {
        local $/; #slurp mode
        $fileallatonce = <$filehandle>;
    }
}

(No, I don't name my vars like this in real code.

If you call read_my_file in an array-context, Perl returns the @filelinebyline, if you need a scalar, you get $filealletonce.

theNbomr · 02-28-2009, 08:12 AM

Quote:

how can i split the HEX values and take just the values that i want? cause in this case is just like one line of string and not seperate values.

You can extract bytes or other chunks of a scalar containing binary data by using the unpack() function.

perldoc -f unpack

--- rod.

Telemachos · 02-28-2009, 10:42 AM

Quote:

Originally Posted by sagik

it's perl ... the "@array.<FILE>" thing is for the lines of the file will be added to the array (using the dot thing in the middle).

I'm happy to admit that I don't know everything about Perl. It's a big language, and there are lots of ways to do things (to mangle a phrase).

Nevertheless, the code you posted originally makes very little sense. Here's what I see:

An infinite while loop with no way to break out of it
An assignment to an array using . which is - I thought - a binary operator to join strings. (I've never seen that used in an @array assignment, and have little idea what it should do in one.)

So, for fun, I rewrite your program to have a finite while loop, and I run it: here's what I have and the output I get:

Code:

telemachus ~/practice $ cat liner 
#!/usr/bin/env perl
use strict;
use warnings;

my $file = $ARGV[0];
open FILE, $file;
my @array;

my $number = 0;
while ($number <= 10) {
  @array = @array.<FILE>;
  print @array;
  $number++;
}

telemachus ~/practice $ ./liner parser 
0#!/usr/bin/env perl
1use strict;
1use warnings;
1
1my %installed_with_deps;
1
1while (<>) {
1    if ( m/^(\S+)\s+has no/ ) {
1        $installed_with_deps{$1} = undef;
1    }
1    elsif ( m/^(\S+).*:$/ ) {

What's happening? Well, every time through the loop, you're assigning this to the array

Code:

@array . <FILE> # concatenate the number of items in @array and one line of FILE

Perl interprets the first bit (@array) as scalar @array which is why it's 0 the first time and 1 every time afterwards. Then, it takes <FILE> also in a scalar context, so it grabs one line from the file each time. The assignment thus gets 0 or 1 concatenated with one line of FILE and assigns that to array. Since you are assigning to the array each time (rather than using push or shift), the old contents of @array are overwritten each time.

So, sure, that's Perl in the sense that it compiles, but it's insane. What are you actually trying to do?

sagik · 02-28-2009, 11:39 AM

first thank you all!!
second,Telemachos, what i've been trying to do is very simple thing - i have a button connected to the computer via usb, it's input written in dev/input/event5.
now, all i want to do is ti create an "Driver" that controls the volume gane of my linux while i'm moving this button clockwise or backwards.

I've discovered that if i read this /dev/input/event5 , i'll see that just the 11th and 12th values in the hex have some changes while playing with the button.

so i want to write a script that allways read the file (and that's way the infinity loop - to keep reading the hex's canges)and with a switch case , check the value and then do it's thing ( in my case, raise up a var with limit of 50 and minimum of 0...consider it the sound volume gane)

Kapish ?

theNbomr · 02-28-2009, 12:16 PM

You probably need to reset the file pointer back to the beginning of the file on each iteration, or close and reopen the file to re-read it on each iteration. The example code shown with 'perldoc -f seek' serves very nearly the same purpose as you require.
--- rod.

Su-Shee · 03-01-2009, 05:20 AM

Quote:

Originally Posted by sagik

first thank you all!!
second,Telemachos, what i've been trying to do is very simple thing - i have a button connected to the computer via usb,

You know about the USB-module...?

http://search.cpan.org/~gwadej/Device-USB-0.28/