Minimally: s/\t/\\t/g;

Something more complete:

my %ws = (
    "\x09" => qw( \t ),  
    "\x0A" => qw( \n ),
    "\x0C" => qw( \f ),  
    "\x0D" => qw( \r ), 
    "\x20" => qw( \s ),
); 
while (<>) {
    s/(\s)/$ws{$1}/g;
    print;
    print "\n";    # keep it line for line. 
}
[download]

Note that printing "\s" for a space is pretty contrived... "\s" really only makes sense in the context of a regular expression. It isn't a real escape for a space.

Something like this would be more general...

  
perl -pe 's/(\s)/sprintf"\\x%02x",ord$1/ge;$_.=$/'
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Update: Added \f and more general one-liner.

-sauoq
"My two cents aren't worth a dime.";

use strict;
use warnings;

my $str = "\tthis is a sample string\nwith various white space charact
+ers\n";
my $str2 = $str;
$str2 =~ tr/\t \n/\0\1\2/;

$str2 =~ s/([\0\1\2])/('\t', '\s', "\\n\n")[ord($1)]/ge;
print $str."\n";
print $str2;
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Prints:

    this is a sample string
with various white space characters

\tthis\sis\sa\ssample\sstring\n
with\svarious\swhite\sspace\scharacters\n
[download]

Update: line breaks per sauoq

There are many non-Perl solutions to this problems. For example, you could use od in unix. Also, many text editors (including UltraEdit and Word in Windows) have the option of displaying whitespace.