http://qs321.pair.com?node_id=699425

sdolancu has asked for the wisdom of the Perl Monks concerning the following question:

I have an executable that outputs to STDERR and STDOUT the following: 
00 0A EF 85 BA 8F AA BC

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(and it keeps going for a while until an end of line character)

I built a perl script I want to pipe this output into. So to run it I would do the

Extractor.exe |& output.pl 
#!/usr/bin/perl
# Name: output.pl
#
while (<>)
  next if !~ m/([0-9a-f])([0-9a-f]) ([0-9a-f])([0-9a-f])/;
  $a = sprintf("%s%s%s%s",$1,$2,$3,$4);
}

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This is so ugly! And to do this for my whole "line" of output, I have to do like fifty captures. I was hoping someone had a more efficient way of doing this. Help please. Thanks, S

Replies are listed 'Best First'.
Re: Help with parsing a string
by moritz (Cardinal) on Jul 22, 2008 at 21:05 UTC
    It seems that you're just trying to remove all whitespaces: 
    s/\s+//g;

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    Of course that doesn't verify your data, so you could use split instead (untested): 

    OUTER:
while (<>){
   chomp;
   my @items = split m/\s/;
   for my $i (@items) {
       last OUTER unless $i =~ m/^[a-f\d]{2}$/;
   }
   print join '', @items;
}

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      If you lines contain other text besides the hex numbers, you can restrict the space removal to just between the hex numbers with: 
       $line =~ s{\b([a-f\d]{2})\s+(?=[a-f\d]{2}\b)}{$1}gi;

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Re: Help with parsing a string
by GrandFather (Saint) on Jul 22, 2008 at 21:38 UTC

    Well, you could:

    use strict;
use warnings;

my $byte = qr/([0-9a-f]{2})/i;

while (<DATA>) {
    my $line = join '', /\b$byte\b/g;
    
    next unless length $line;
    print "$line\n";
}

__DATA__
00 0A EF 85 BA 8F AA BC
Wibble
00 0A EF 85 BA 8F AA BC

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    Prints:

    000AEF85BA8FAABC
000AEF85BA8FAABC

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    Perl is environmentally friendly - it saves trees
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Re: Help with parsing a string
by jethro (Monsignor) on Jul 22, 2008 at 21:14 UTC
    Well, if you want to print those 4 chars, just do 
    print $1,$2,$3,$4;

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    Even better, if all you want is just to eliminate spaces in that string, do 
    s/ //g;
print;

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    If that is not what you want, you have to be more specific.
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Re: Help with parsing a string
by toolic (Bishop) on Jul 23, 2008 at 01:09 UTC
    Yet another way to represent a hexadecimal digit is to use the POSIX character class (see perlre): 
    [[:xdigit:]]

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