Problem with sysread()

  Hi, everyone,

I've met some problem while practice my perl. It seems that in some 
condition,
sysread() doesn't work?

codes here:

--------------------------------------------
#!/usr/bin/perl -w
use strict;
$| = 1;

open my $file, "<", "test.txt" or die;
## if these add these 2 lines, sysread doesn't work ?
## my $first_line = <$file>;
## print "first_line is : $first_line";
my $ctr = 0;
while(1){
    my ($data, $ret);
    $ret = sysread $file, $data, 1;
    last if $ctr ++ >= 20;
    print "ret : $ret, data : ", unpack("H2", $data), "\n";
}
--------------------------------------------

and file "test.txt":

--------------------------------------------
line1
line2
--------------------------------------------

and the output is:

--------------------------------------------
ret : 1, data : 6c
ret : 1, data : 69
ret : 1, data : 6e
ret : 1, data : 65
ret : 1, data : 31
ret : 1, data : 0d
ret : 1, data : 0a
ret : 1, data : 6c
ret : 1, data : 69
ret : 1, data : 6e
ret : 1, data : 65
ret : 1, data : 32
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
--------------------------------------------

which is thought to be correct.

*My question is*: when I unquote the two lines in the code (which I 
think should put
the first line["line1\n\r"] into $first_line, and sysread will only get 
the second line),
sysread() cannot get anything. The output is just:

--------------------------------------------
first_line is : line1
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
ret : 0, data :
--------------------------------------------

Is there anything wrong with my codes ?

Peter

• Problem with sysread() by Peter Xu
• Re: Problem with sysread() by John W. Krahn
• Re: Problem with sysread() by John W. Krahn