Match over multiple lines perl regular expression

Question

I have a file like this:

01 00 01 14 c0 00 01 10 01 00 00 16 00 00 00 64
00 00 00 65 00 00 01 07 40 00 00 22 68 61 6c 2e
6f 70 65 6e 65 74 2e 63 6f 6d 3b 30 30 30 30 30
30 30 30 32 3b 30 00 00 00 00 01 08 40 00 00 1e
68 61 6c 2e 6f 70 65 6e 65 74 2d 74 65 6c 65 63
6f 6d 2e 6c 61 6e 00 00 00 00 01 28 40 00 00 21
72 65 61 6c 6d 31 2e 6f 70 65 6e 65 74 2d 74 65
6c 65 63 6f 6d 2e 6c 61 6e 00 00 00 00 00 01 25
40 00 00 1e 68 61 6c 2e 6f 70 65 6e 65 74 2d 74
65 6c 65 63 6f 6d 2e 6c 61 6e 00 00 00 00 01 1b
40 00 00 20 72 65 61 6c 6d 2e 6f 70 65 6e 65 74
2d 74 65 6c 65 63 6f 6d 2e 6c 61 6e 00 00 01 02
40 00 00 0c 01 00 00 16 00 00 01 a0 40 00 00 0c
00 00 00 01 00 00 01 9f 40 00 00 0c 00 00 00 00
00 00 01 16 40 00 00 0c 00 00 00 00 00 00 01 bb
40 00 00 28 00 00 01 c2 40 00 00 0c 00 00 00 00
00 00 01 bc 40 00 00 13 31 39 37 37 31 31 31 32
32 33 31 00

I am reading the file and then finding certain octets and replacing them with tags:

while(<FH>){
    $line =~ s/(00 00 00 64)/<incr4>    /g;
    $line =~ s/(00 00 00 65)/<incr4>    /g;
    $line =~ s/(30 30 30 30 30 32)/<incr6ascii:999999:0>/g;
    $line =~ s/(31 31 32 32 33 31)/<incr6ascii:999999:0>/g;
    print OUTPUT $line;
}

So for example, 00 00 00 64 would be replaced by the <incr4> tag. This was working fine, but it doesn't seem to able to match over multiple lines any more. For example the pattern 31 31 32 32 33 31 runs over multiple lines, and the regular expression doesn't seem to catch it. I tried using /m /s pattern modifiers to ignore new lines but they didn't match it either. The only way around it I can come up with, is to read the whole file into a string using:

undef $/;
my $whole_file = <FH>;
my $line = $whole_file;
$line =~ s/(00 00 00 64)/<incr4>    /g;
$line =~ s/(00 00 00 65)/<incr4>    /g;
$line =~ s/(30 30 30 30 30 32)/<incr6ascii:999999:0>/g;
$line =~ s/(31 31 32 32 33 31)/<incr6ascii:999999:0>/g;
print OUTPUT $line;

This works, the tags get inserted correctly, but the structure of the file is radically altered. It is all dumped out on a single line. I would like to retain the structure of the file as it appears here. Any ideas as to how I might do this?

/john

Answer 1

The trick here is to match the class of all space like characters \\s :

my $file = do {local (@ARGV, $/) = 'filename.txt'; <>}; # slurp file

my %tr = (  # setup a translation table
    '00 00 00 64'       => '<incr4>',
    '00 00 00 65'       => '<incr4>',
    '00 30 30 30 30 32' => '<incr6ascii:999999:0>',
    '31 31 32 32 33 31' => '<incr6ascii:999999:0>',
);

for (keys %tr) {
    my $re = join '\s+' => split;  # construct new regex

    $file =~ s{($re)}{
       $1 =~ /\n/ ? "\n$tr{$_}" : $tr{$_}  # if octets contained \n, add \n
    }ge  # match multiple times, execute the replacement block as perl code
}
print $file;