Did you try with String::Escape?

Ciao, Valerio

    #!/usr/bin/perl -wl

    use strict;

    my %esc = (
               '\0' => "\0",
               '\a' => "\a",
               '\b' => "\b",
               '\t' => "\t",
               '\n' => "\n",
               '\v' => "\013",
               '\f' => "\f",
               '\r' => "\r",
              );


    my $literal = 'aaa\tbbb\nccc\tddd\t\\\\end';

    (my $escaped = $literal) =~ s/(\\.)/exists $esc{$1} ? $esc{$1} : $
+1/eg;

    print $literal, "\n";

    print $escaped;

    __END__
    Prints:
    aaa\tbbb\nccc\tddd\t\\end

    aaa    bbb
    ccc    ddd    \\end
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Backslash has to be escaped in single quoted strings so it doesn't require a substitution.

The escape characters shown are the usual shell escapes. Perl adds a few more such as \e. Note the exists() isn't strictly required.

--
John.

This is a lot more complex than it needs to be, and only recognizes a small subset of possible scapes. Plus, there are escapes with an argument (like \012 or \x0A or \cJ for newline), which would make a very big hash or more complex code.

A regex-with-eval-substitution like the ones below is a better solution.

my $x = '\t\t\n\t\n\n';
eval "\$x = \"$x\"";
print "$x";
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Just for fun, try that with:

my $x = '";warn q[this is code!] for 1..20;"';
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:-)

Hint: Don't use eval() carelessly... your version allows arbitrary code to be placed in the input string, which will get executed

Good point. I don't typically use eval on data that comes in externally -- only on data my program controls.

My first shot at the commandline might provide a start for you:

perl -e "\$test='a\n\nb'; \$test =~ s/(\\\\\\w)/pack(\"h\",\"\$1\")/ge
+;print \$test"
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a

 b
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Update:pure luck that it kind of worked with \n, basically b***sh*t.

Update II:I was asked to beep 'the word' out, so that corporate filters don't choke on this node. I'm in no way expecting anybody in here to be offended by it :-)

regards,
tomte

You are going in the right direction with the evalled substitution, but consider what you end up with: eval "\n", which is much the same as

eval {
}
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The obvious next thing to try is adding the quotes:

  s/(\\\w)/"$1"/eg;
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Adding a second evaluation step is enough to achieve the desired result:

  s/(\\\w)/qq{"$1"}/eeg;
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That contains a bug:

The input string:  \\n should be interpreted as:  \n (as in, the backslash escapes the backslash) but in your case, it becomes a backslash followed by a newline.

The solution is:  s/(\\.)/qq["$1"]/eegs

Btw, the reason "$1"/e isn't sufficient is because when using /e it doesn't interpolate before evaluating, so the expression really becomes "$1" which is identical to $1 - no change happens at all.

With qq["$1"]/ee however it'll interpolate $1 into a double-quoted string the first time, and then evaluates that double-quoted string

•Update: to also support multi-char escapes:

s/(\\(?:\d{1,3}|x[a-fA-F\d]{1,2}|x\{\w*\}|c.|N\{\w*\}|.))/qq["$1"]/eeg
+s
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(not fully tested)

package Escape;
use Exporter;
# simple escape module for html stuff
# use Escape;
# my $data = escape($string_to_escape);
@ISA         = qw(Exporter);
@EXPORT      = qw(escape);

sub escape {
my $data = shift;
$data =~ s/\%/%25/g;$data =~ s/\t/%9/g;$data =~ s/\n/A/g;
$data =~ s/ /%20/g;$data =~ s/\!/%21/g;$data =~ s/\"/22/g;
$data =~ s/\#/%23/g;$data =~ s/\$/24/g;$data =~ s/\&/%26/g;
$data =~ s/\'/%27/g;$data =~ s/\(/%28/g;$data =~ s/\)/%29/g;
$data =~ s/\*/%2A/g;$data =~ s/\+/%2B/g;$data =~ s/\,/%2C/g;
$data =~ s/\-/%2D/g;$data =~ s/\./%2E/g;$data =~ s/\//%2F/g;
$data =~ s/\:/%3A/g;$data =~ s/\;/%3B/g;$data =~ s/\</%3C/g;
$data =~ s/\=/%3D/g;$data =~ s/\>/%3E/g;$data =~ s/\?/%3F/g;
$data =~ s/\@/%40/g;$data =~ s/\[/%5B/g;$data =~ s/\\/%5C/g;
$data =~ s/\]/%5D/g;$data =~ s/\^/%5E/g;$data =~ s/\_/%5F/g;
$data =~ s/\`/%60/g;$data =~ s/\{/%7B/g;$data =~ s/\|/%7C/g;
$data =~ s/\}/%7D/g;$data =~ s/\~/%7E/g;
return $data;
}

1;
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it was pointed out to me that I was way off the mark.. sorry... perhaps this little snippet will give you something to experiment with that may provide you with the insight you are hoping to find

use strict;
#Experiment with commenting out the next line!
binmode STDIN, ":raw";
print "Just hit the enter key!\n";
my $char = <STDIN>;
my $bits = unpack "B*", $char;
print "[Enter]'ed  bits: $bits \n";
my $bits = unpack "B*", '\n';
print "The literal bits: $bits \n";
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Code:

$x = '\n';
print "var  :==$x==\n";
print "eval :==",
      eval( qq{ sprintf "%s","$x" } ),
      "==\n";

Output:

var  :==\n==
eval :==
==

You need double-quotish interpolation *twice*. :)