perl while loop substitution

casperdaghost · 02-19-2012, 12:48 AM

I have a log file which is very dense
You cant see them, but there is a 'CTRL-A' character before each "numeric tag='. The escape character for the CTRL-A is '0001'

Code:

casper@casper-SX280:~$ more dense_file  | head -1
>8=FIX.4.29=027835=834=11605249=NQPX56=S085H652=20120217-14:35:31.191128=S15BX257=6T0050=INET11=6T0010005924641=6T0010005924537=92392017=-11185520=0150=539=5109=MLCO55=NTAP54=538=20032=031=0.0151=20014=06=0.044=42.780040=247=A29=176=INET111=018=N59=558=Replaced10=085
casper@casper-SX280:~$

anyhow I can sed them out with 's/\x01/ /g' - look at those nice spaces in the dense_log !!!

Code:

casper@casper-SX280:~$ more dense_file  | sed -e 's/\x01/ /g' | head -1
> 8=FIX.4.2 9=0278 35=8 34=116052 49=NQPX 56=S085H6 52=20120217-14:35:31.191 128=S15BX2 57=6T00 50=INET 11=6T00100059246 41=6T00100059245 37=923920 17=-111855 20=0 150=5 39=5 109=MLCO 55=NTAP 54=5 38=200 32=0 31=0.0 151=200 14=0 6=0.0 44=42.7800 40=2 47=A 29=1 76=INET 111=0 18=N 59=5 58=Replaced 10=085

So I wanted to write something up in perl - this works

Code:

#!/usr/bin/perl
use strict ;
open (FILE , "dense_file") or die "cannot open up the file";
while (<FILE>) {
        s/\x01/ /g;
        print $_;
        sleep 1;
}

However when I assign a variable to the default varible $_ it stops working.

Code:

#!/usr/bin/perl
use strict ;
open (FILE , "dense_file") or die "cannot open up the file";
while (<FILE>) {
        my $line = $_;
        s/\x01/ /g;
        print $line;
        sleep 1;
}

grail · 02-19-2012, 07:29 AM

I would think maybe it is an order thing, try switching the sed portion and the assignment.

aluchko · 02-19-2012, 02:09 PM

I agree with grail,

Code:

        my $line = $_;
        s/\x01/ /g;
        print $line;

You assign $line to default variable, then perform a substitution on the default variable, which reassigns the default variable to the result of the substitution, but leaving $line with the original value.

Switching the order to

Code:

        s/\x01/ /g;
        my $line = $_;
        print $line;

Will fix the problem

chrism01 · 02-19-2012, 07:07 PM

As aluchko said, you're printing one var, but substituting the other one.
I would use

Code:

my $line;
while (defined( $line = <FILE>) )
{
        $line =~ s/\x01/ /g;
        print $line;

PS This is what I used to test

Code:

$var1="x\x01=dw";
print length($var1)." X${var1}X\n";

$var1 =~ s/\x01/ /;
print length($var1)." X${var1}X\n";

$var1="x\x01=dw";
$var1 =~ s/\x01//;
print length($var1)." X${var1}X\n";

casperdaghost · 02-19-2012, 08:08 PM

Yeah chrism01 I came to a similiar conculsion myself
The latest iteration of this script stops once it reaches a certain time frame
and substutes values.

Code:

#!/usr/bin/perl 
use strict ; 
open (FILE , "roo") or die "cannot open up the file"; 
while (<FILE>) { 
        my $line = $_; 
        if ($line !~ /52=20120217-14:35:31.399*/) {

                $line =~ s/\x01/ /g; 
                $line =~ s/INET/marmaduke/g; 
                $line =~ s/MLCO/peanut/g; 
                print $line; 
                #sleep 1; 
        }
}

notice the marmaduke and the peanut
I dont know why I have to use the matching operator =~ but it works.

Code:

casper@casper-SX280:~$ ./perl_parse3 | head -1
> 8=FIX.4.2 9=0278 35=8 34=116052 49=NQPX 56=S085H6 52=20120217-14:35:31.191 128=S15BX2 57=6T00 50=marmaduke 11=6T00100059246 41=6T00100059245 37=923920 17=-111855 20=0 150=5 39=5 109=peanut 55=NTAP 54=5 38=200 32=0 31=0.0 151=200 14=0 6=0.0 44=42.7800 40=2 47=A 29=1 76=marmaduke 111=0 18=N 59=5 58=Replaced 10=085

i really don't see too many examples of while loop perl substitutions - I thought that this is what perl is for?

chrism01 · 02-19-2012, 08:14 PM

As per my example, no need to copy $_ to $line, just assign it in the while().
Also, '=~' is the 'match' regex operator in Perl; not-match is '!~', see
http://perldoc.perl.org/perlrequick.html
http://perldoc.perl.org/perlretut.html