Something like this...

if( $string =~ m/MTV\s*=\s*(0x[a-f0-9]+)/i ) {
    print $1, "\n";
}
[download]

It's just a matter of anchoring to something predictable, and capturing the right pattern. ;)

Update: By the way, [a-f0-9] could also be represented by [[:xdigit:]] The POSIX character class for a hexidecimal digit. In that case, the RE would look like this:

if( $string =~ m/MTV\s*=\s*(0x[[:xdigit:]]+)/ ) {
    print $1, "\n";
}
[download]

It's not really gaining anything to spell it that way, but perhaps could be seen as a little clearer reading.

How about:

($num) = $string =~ /\bMTV\s*=\s*(0x[0-9a-fA-F]+)/;
die("Bad Input!") unless defined $num;
print("Found $num (", hex($num), " in decimal)\n");
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my $data = join '', <DATA>;
if($data =~ /(0x\w+)/) {
    print "$1\n";
}

__DATA__
1:05:02.599,xx:MTV = 0x2f7c:COOL_CALL, an option = 11
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$_ = q{1:05:02.599,xx:MTV = 0x2f7c:COOL_CALL, an option = 11};

m/(?<==)\s?(.+)\s?(?=:)/;   # $1 eq 0x2f7c
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Hi, just try this,

my $input='1:05:02.599,xx:MTV = 0x2f7c:COOL_CALL, an option = 11';
my $match;

($match) = $input =~ m#:(?:\w+)?\s*=\s*(0x[a-f0-9]+):#i;
 
print "$match";
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Instead of providing an example string, with some notes, rethink your problem:
- what is the exact pattern my strings follows?
- what are the constant parts, which parts change?
- what rules apply to the changing parts?

You will notice that, ooce you gat the answers to the above questions, you have the solution to your problem

Paul

Tend to agree with most of your points, rev_1318, but having a hard time trying to parse their applicability here... because OP wrote ":COOL_CALL, an option" is static" -- which is pretty much an ironclad (if, 'incomplete')answer for part 2 of your question.

Seems to me that knowing we have a (mutable) hex value followed immediately by a ":COOL_CALL" makes writing a regex perfectly straightforward... at least in the practical world where the string 'colon, COOL, uline, CALL" seems unlikely to appear accidentally.

OTH, and to highlight my general agreement though, OP does NOT say that there will be a desired hex value immediately preceeding ":COOL_CALL" and (ymmv) I can only INFER (from the fact that its variability/non_variability is NOT addressed) that ",xx:MTV = " is potentially variable, and hence, should not be used by the regex.

ie, greater precision in the question from OP can be a big help

TIMTOWTDI

>perl -le '$s="1:05:02.599,xx:MTV = 0x2f7c:COOL_CALL, an option = 11";
+ 
(undef, $s) = unpack "a21 a6", $s; print $s'
0x2f7c
>perl -le '$s="1:05:02.599,xx:MTV = 0x2f7c:COOL_CALL, an option = 11";
+ 
$i=index $s, ":COOL_CALL"; print substr $s, $i-6, 6'
0x2f7c
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Cheers,
R.