They're unprintable, so you can't see them by definition. You could replace them with some form of representation. For example, 

sub unchomp { $_ = $_.$/ foreach @_ ? @_ : $_; }

while (<$sock>) {
   chomp;  # Don't want to transform the newline.
   s/([^[:print:]])/sprintf("\\x{%02X}", ord($1))/eg;
   unchomp;
   print;
}

[download]
Untested.

Update: Tested. Fixed bugs.

Update: Here's an alternative representation (for charsets based on ASCII): 

sub unchomp { $_ = $_.$/ foreach @_ ? @_ : $_; }

while (<$sock>) {
   chomp;  # Don't want to transform the newline.
   s/([\x01-\x1F])/'^' . chr(ord('@')+ord($1))/
   s/([^[:print:]])/sprintf("\\x{%02X}", ord($1))/eg;
   unchomp;
   print;
}

[download]

The first program outputs
test\x{1}\x{2}\x{1D}test
and the second outputs
test^A^B^]test
for the result of the Perl expression
"test".chr(1).chr(2).chr(29)."test"

In reply to Re: I want to know exactly what comes through a socket by ikegami
in thread I want to know exactly what comes through a socket by ivanatora

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