[ale] Perl pack question

[Ed Cashin]

These three programs print 12345679 when you pipe packinput to pack to
packoutput as shown in the comment for packoutput.c.

/* packinput.c */
#include <unistd.h>

int main(void)
{
    int i = 0x12345678;

    return write(STDOUT_FILENO, &i, sizeof i) != sizeof i;
}

#! /opt/local/bin/perl -w
# pack

use strict;

&go;

sub go {
    # read "packed" binary data
    my $data = do { local $/; <STDIN> };

    my $i = unpack("i", $data);
    print pack("i", $i + 1);
}

/* packoutput.c
(set -xe
 for i in in out; do
   gcc -Wall -W pack${i}put.c -o pack${i}put
 done
./packinput | ./pack | ./packoutput)
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(void)
{
    int i;

    if (read(STDIN_FILENO, &i, sizeof i) == sizeof i)
        printf("%x\n", i);
    else
        exit(EXIT_FAILURE);
    return 0;
}



On Fri, Feb 15, 2013 at 9:32 AM, Geoffrey Myers <lists at serioustechnology.com
> wrote:

> So I'm trying to modify a binary file with perl. All is going well except
> one issue. I need to change an integer value. I can successfully retrieve
> the value by using:
>
> unpack("S", $var);
>
> I assumed, incorrectly that I could do this to reset the value:
>
> pack("S", $newvar);
>
> Not working. Suggestions?
>
> --
> From my iPhone
> Geoffrey Myers
> _______________________________________________
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-- 
  Ed Cashin <ecashin at noserose.net>
  http://noserose.net/e/
  http://www.coraid.com/
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