On 10/8/18 1:46 AM, Peter Pentchev wrote:
On Mon, Oct 08, 2018 at 01:38:54AM -0700, ToddAndMargo via perl6-users wrote:
On 10/8/18 1:34 AM, Peter Pentchev wrote:
On Mon, Oct 08, 2018 at 01:25:31AM -0700, ToddAndMargo via perl6-users wrote:
Hi All!
Question: I am using `read` to read the first 400 bytes of an unknown file
(could be a binary file). The 400 bytes go into a variable
of type "Buf". This is not a string.
p6 'my $fh=open "/home/linuxutil/To", :r; my Buf $f = $fh.read( 400 );
$fh.close;'
Now in $f, I want to look at each byte one at a time for a
bitwise pattern using bitwise AND.
How do I address each byte?
`dd` seems to get me the information I need, but it prints it:
$ p6 'my $fh=open "/home/linuxutil/To", :r; my Buf $f = $fh.read( 10 );
$fh.close; dd $f;'
Buf[uint8] $f = Buf[uint8].new(87,111,114,100,80,114,111,0,0,0)
An array of bytes would be great.
Point a browser at https://docs.perl6.org/ and click on "Types" in
the top ribbon. You will see a list of all the Perl 6 built-in types;
"Buf" is there near the top. Click on "Buf".
Been there, done that already. No idea what it said.
OK, so for future reference, when you see a reference page for a type
like that, look at the left side to see which roles it implements and
which methods it takes from these roles. As I wrote below, in this case
the Positional role could have been a clue that you can address a Buf
object using [index] (I seem to remember another thread of yours with
people explaining the Positional role).
Also, in the future, take a look at the code in the examples; in this
particular case, the use of "$b[1]" could have been a hint.
Now there are two clues as to what you want: one of them is that
the table of contents on the left has a section "Routines supplied by
role Positional", and the other one is that the very first example
has a line saying "$b[1] = 42".
When I first looked at it, I was trying to convert it
into a latin-1 string. So I skipped over it looking
for Stringy or Str or something similar.
When I posted this, I changed my thinking to "why do I want
it in a string?" I just want an array of bytes. Had I
looked again, "$b[1] = 42" would have made total sense.
So you can use a Buf object as an array of whatever it contains.
G'luck,
Peter
Hi Peter,
Perfect! Exactly what I was after!
Glad it worked out for you!
G'luck,
Peter
Thank you for helping me with this. I can be thick at times.
-T
