Article 7359 of comp.lang.perl:
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From: Tom Christiansen <tchrist@cs.Colorado.EDU>
Subject: Re: Expanding a string with non-printing characters
Message-ID: <CFLsts.DEB@Colorado.EDU>
Originator: tchrist@wraeththu.cs.colorado.edu
Sender: news@Colorado.EDU (USENET News System)
Reply-To: tchrist@cs.colorado.edu (Tom Christiansen)
Organization: University of Colorado, Boulder
References: <1993Oct28.002016.28662@parc.xerox.com>
Date: Thu, 28 Oct 1993 10:51:27 GMT
Lines: 121

:-> In comp.lang.perl, griswold@adoc.xerox.com writes:
:I can't think of a graceful way of doing this.  (I can think of
:several yucky ways.) I know there shoule be a one or two line
:solution.  It's a common problem:
:
:I have a variable, $foo, which may contain any number of control
:characters.  I want to expand the control characters to their
:string representation: "^A" for control-A, "^[" for ESC, and 
:so forth.
:
:Suggestions? Places in TFM to R? Send me mail and I will summarize
:if interest warrants.

Well, you could do this:

    s/([\0-\37\177])/sprintf("^%c",ord($1)^64)/eg;

Or you could get fancy:

#!/bin/sh
# This is a shell archive.  Remove anything before this line,
# then unpack it by saving it in a file and typing "sh file".
#
# Wrapped by  on Thu Oct 28 04:49:31 MDT 1993
# Contents:  pit
 
echo x - pit
sed 's/^@//' > "pit" <<'@//E*O*F pit//'
#!/usr/bin/perl 

$debug = 0;
&init;
while (<>) {
    print "line is: ", &printable($_), "\n";
    print "\$_ = '", &evalable($_), "'\n";
} 
exit;

###############

sub printable { 
    local($_) = @_;
    $_ = &xlate($_,0);
}

sub evalable {
    $_ = &xlate($_,1);
}

###############
sub init { 

$code = <<'EOF';
    sub xlate { 
	local($_, $evalit) = @_;
	if ($evalit) {
	    s/(['\\])/\\$1/g;
	    s/([\200-\377])/sprintf("\\%03o",ord($1))/eg; 
	} else {
	    s/([\200-\377])/sprintf("M-%c",ord($1)&0177)/eg; 
	}
EOF
$spec_code = "\n";

while (<DATA>) {
    ($char, $xlate, $comment) = split(' ', $_, 3);
    #$char = eval q("$char") if $char =~ /\\/;
    $xlate =~ s/\\/\\\\/;  
    $special .= $char;
    $spec_code .= <<"EOF";
	    s/$char/$xlate/g;
EOF
} 

$code .= <<EOF;
	if (/[$special]/) {
	    $spec_code
	}
EOF
$code .= <<'EOF';
	s/([\0-\37\177])/sprintf("^%c",ord($1)^64)/eg;
EOF
$code .= <<'EOF';
	return $_;
    } 
EOF

print $code if $debug;
eval $code;
if ($@) {
    ($line) = $@ =~ /line\s*(\d+)/;
    die unless $line;
    @lines = split("\n", $code);
    warn "$0: error in compilation:\n\t$@\n";
    for $i ( ($line - 2) .. $line) {
	printf "%3s %2d: %s\n", 
	    ($i+1 == $line) ? "==>" : '',
	    $i+1, $lines[$i]; 
    } 
    die "\n$0: Cannot compile printable functions\n";
} 

}

__END__
\0	\0	null
\t	\t	tab
\n	\n	newline
\r	\r	return
\f	\f	formfeed
\010	\b	backspace
\a	\a	bell
\e	\e	escape
@//E*O*F pit//
chmod u=rwx,g=rwx,o=rx pit
 
exit 0
-- 
    Tom Christiansen      tchrist@cs.colorado.edu       
      "Will Hack Perl for Fine Food and Fun"
	Boulder Colorado  303-444-3212