The read and getc Perl functions correspond to the fread and fgetc C-lib functions. The C-lib I/O functions are buffered. When you ask for X bytes, it might actually read X+Y bytes internally. Subsequent reads will read from the Y bytes first.

This is very good in your case, because you keeps asking for one byte. Most of the time, you'll just be reading from the buffer, which is faster than doing a real read.

How do the C-lib functions get their data? Through system calls. sysread is Perl's interface to the read system call. The system I/O functions are not buffered.

A key difference between read and sysread is that read(FH, $buf, $bytes) will wait for $bytes bytes to be available, whereas sysread(FH, $buf, $bytes) will return as soon as bytes become available. $bytes is simply a maximum for sysread. I took advantage of this to read in more than one byte at a time.

C-lib and system functions should not both be used on the same file handle.

Your usage of getc is incorrect. It returns undef at the end of input, not false.

The select STDOUT; is useless. 

print '
  use warnings;
  use strict;
  $| = 1;
  $_ = "";
  while (defined($chr = getc DATA)) {
      $_ .= $chr;
      next unless $chr =~ /\s/;
      s/' . (quotemeta $password) . '/removed/ig;
      print;
      $_ = "";
  }
  print;
  __DATA__
';

[download]

(Update: Nevermind, next unless /\s/; is buggy.

Probably faster: 

print '
  use warnings;
  use strict;
  $| = 1;
  $_ = "";
  for (;;) {
    sysread(DATA, $_, 4096, length())
      or last;
    next unless /\s/;
    s/' . (quotemeta $password) . '/removed/ig;
    print;
    $_ = "";
  }
  print;
  __DATA__
';

[download]

)

In reply to Re^3: Filtering passwords from the output of a script by ikegami
in thread Filtering passwords from the output of a script by quester

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