How to convert single quoted string to double quoted string so it gets interpreted?

For example I have,

my $str = '\t';
print "My String is ".$str;

I want the output to interpret the tab character and return something li开发者_高级运维ke:

"My String is \t"

I am actually getting the value of the string from the database, and it returns it as a single quoted string.

String::Interpolate does exactly that

$ perl -MString::Interpolate=interpolate -E 'say "My String is [". interpolate(shift) . "]"' '\t'
My String is [  ]

'\t' and "\t" are string literals, pieces of Perl code that produces strings ("\","t" and the tab character respectively). The database doesn't return Perl code, so describing the problem in terms of single-quoted literals and double-quoted literals makes no sense. You have a string, period.

The string is formed of the characters "\" and "t". You want to convert that sequence of characters into the tab character. That's a simple substitution.

s/\\t/\t/g

I presume you don't want to deal with just \t. You can create a table of the sequences.

my %escapes = (
    "t" => "\t",
    "n" => "\n",
    "\" => "\\",
);

my $escapes_pat = join('', map quotemeta, keys(%escapes));
$escapes_pat = qr/[$escapes_pat]/;

s/\\($escapes_pat)/$escapes{$1}/g;

You can follow the technique in perlfaq4's answer to How can I expand variables in text strings?:

If you can avoid it, don't, or if you can use a templating system, such as Text::Template or Template Toolkit, do that instead. You might even be able to get the job done with sprintf or printf:

my $string = sprintf 'Say hello to %s and %s', $foo, $bar;

However, for the one-off simple case where I don't want to pull out a full templating system, I'll use a string that has two Perl scalar variables in it. In this example, I want to expand $foo and $bar to their variable's values:

my $foo = 'Fred';
my $bar = 'Barney';
$string = 'Say hello to $foo and $bar';

One way I can do this involves the substitution operator and a double /e flag. The first /e evaluates $1 on the replacement side and turns it into $foo. The second /e starts with $foo and replaces it with its value. $foo, then, turns into 'Fred', and that's finally what's left in the string:

$string =~ s/(\$\w+)/$1/eeg; # 'Say hello to Fred and Barney'

The /e will also silently ignore violations of strict, replacing undefined variable names with the empty string. Since I'm using the /e flag (twice even!), I have all of the same security problems I have with eval in its string form. If there's something odd in $foo, perhaps something like @{[ system "rm -rf /" ]}, then I could get myself in trouble.

To get around the security problem, I could also pull the values from a hash instead of evaluating variable names. Using a single /e, I can check the hash to ensure the value exists, and if it doesn't, I can replace the missing value with a marker, in this case ??? to signal that I missed something:

my $string = 'This has $foo and $bar';

my %Replacements = (
    foo  => 'Fred',
    );

# $string =~ s/\$(\w+)/$Replacements{$1}/g;
$string =~ s/\$(\w+)/
    exists $Replacements{$1} ? $Replacements{$1} : '???'
    /eg;

print $string;

Well, I just tried below workaround it worked. Please have a look

my $str1 = "1234\n\t5678";
print $str1; 
#it prints 
#1234
#     5678

$str1 =~ s/\t/\\t/g;
$str1 =~ s/\n/\\n/g;

print $str1; 
#it prints exactly the same
#1234\n\t5678