PERL question (help needed)

laoisfan · 07-07-2005 02:58PM #1

Hi

I am writing a wee perl script which will do the following on UNIX:

1. ipcs -opq | grep q # grab the message queues.
2. extract the hex value i.e. the 3rd field.
3. convert the hex value to decimal.
4. then use the decimal value as lookup in a c-header file (for some application).

I am doing part 1 as follows:

open(PIPE, "ipcs -opq | grep q |") or die "Can't run program: $!\n";
while(<PIPE>) {
# HELP NEEDED HERE!!
}

How do I extract the hex value? I did try the following but it did not work for me:

open(PIPE, "ipcs -opq | grep q | awk '{print $3}' |")

Can somebody please enlighten me?

Thanks - laoisfan

Syth · 07-07-2005 03:28PM

Regular expressions.

Use a regulat expression to parse each line to get the hex value. Not sure about the hex -> dec, I'm sure there's a function to do it. Then just open the c-header file and use more regex goodness to do the lookup.

hostyle · 07-07-2005 05:32PM

Can you provide an example of the output from "ipcs -opq" ? I should be able to help you then.

daymobrew · 07-07-2005 06:12PM

Here is the output from the command run on a Solaris 9 box:

$ ipcs -opq

IPC status from <running system> as of Thu Jul  7 18:10:51 BST 2005
T         ID      KEY        MODE        OWNER    GROUP CBYTES  QNUM LSPID LRPIDMessage Queues:
q          0   0x61004aa5 --rw-------     root     root     13     1   527   527

I would have thought you could do something like, in shell...

# Backquotes around command
for f in `ipcs -opq | grep "^q" | awk '{print $3}'`
do
    grep "$f" /dir/to/headers
done

hostyle · 07-07-2005 08:54PM

#!/usr/bin/perl -w

use strict;

my @values;

while (<DATA>) {
  if (/^q/) {
    my @s = split /\s+/;
    push @values, hex($s[2]);
  }
}

foreach (@values) {
	print "$_\n";
}

__DATA__

T         ID      KEY        MODE        OWNER    GROUP CBYTES  QNUM LSPID LRPIDMessage Queues:
q          0   0x61004aa5 --rw-------     root     root     13     1   527   527

No need for your grep now either. Hope that helps.

laoisfan · 08-07-2005 08:01AM

daymobrew wrote:
I would have thought you could do something like, in shell...
# Backquotes around command
for f in `ipcs -opq | grep "^q" | awk '{print $3}'`
do
    grep "$f" /dir/to/headers
done

Hi

Yes - I was doing that in shell. Howeve, I could not come up with an elegant way of converting the value from hex to decimal in shell scripting. Perl has a one liner way of doing it as follows:

$dec = sprintf("%d", 0x80);

So I thought I could throw the sprintf in a while loop in perl, convert the hex vale and then do a lookup in the header file.

If anyone knows of an easy way to convert hex to dec in shell...........

Thanks.

laoisfan · 08-07-2005 08:02AM

thanks!! nice one!!

laoisfan · 08-07-2005 08:08AM

#!/usr/bin/perl -w

use strict;

my @values;

open(DATA, "ipcs -opq | grep q |") or die "Can't run program: $!\n";
while (<DATA>) {
  if (/^q/) {
        my @s = split /\s+/;
        push @values, hex($s[2]);
  }
}

foreach (@values) {
        print "$_\n";
}

close DATA;

thanks for all the help guys, much appreciated!!

I can now add in the bits that will lookup the decimal value in the C-header files.

hostyle · 08-07-2005 11:39AM

open(DATA, "ipcs -opq | grep q |") or die "Can't run program: $!\n";

Two things:

1. Don't use DATA as the handle to open(), its reserved for the __DATA__ block (which I was using in my example).
2. No need for your "| grep q " as the below is doing just that - checking for a q at the beginning of a line.

  if (/^q/) {

PERL question (help needed)

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