• String literal "\u6b63" creates the string 6b63 (since \u uppercases the next character). To create the string \u6b63, you need to use string literal "\\u6b63".

• You can't interpolate into the middle of an escape sequence (like "\x{$_}"). Interpolation and escapes occur at the same level.

• You're passing the hex representation of a number to chr, but chr expects a number. You can use hex to do the conversion.

• $_ doesn't contain the hex number of the character as you'd need in the escape sequence. It contains the decoded character already (as returned by chr).

use open ':std', ':locale';  # So stuff you print shows up right.

$_ = "\\u6b63";
print "orig string length is ", length($_), "\n";
print "orig string is $_\n";

s/\\u(.{4})/chr(hex($1))/eg;
print "decoded string length is ", length($_), "\n";
print "decoded string is $_\n";
[download]

orig string length is 6
orig string is \u6b63
decoded string length is 1
decoded string is 正

Update: Added lots