printf: hex & octal escapes (#528)

* When testing against bash-builtin and GNU version of printf command, octal escapes allow 3 digits but input >255 are interpreted as mod-256 (e.g. \400 wraps around to \0)
* For hex escapes, only 2 digits are allowed so entering input above FF is not possible anyway
* The hex digits can be mixed case, but the "x" prefix must be lowercase
* test1: terminate word list with NUL: perl printf '%s\0' over here
* test2: windows line-ending string with hex: perl printf 'hey\xd\xa'

bin/printf

@@ -77,6 +77,18 @@ sub parse_fmt {
     }
 }
 
+sub oct2char {
+    my $str = shift;
+    my $n = oct($str) & 255;
+    return chr($n);
+}
+
+sub hex2char {
+    my $str = shift;
+    my $n = hex($str) & 255;
+    return chr($n);
+}
+
 sub escape_str {
     my $str = shift;
     $str =~ s/\\a/\a/g;
@@ -86,6 +98,8 @@ sub escape_str {
     $str =~ s/\\r/\r/g;
     $str =~ s/\\t/\t/g;
     $str =~ s/\\v/\x0b/g;
+    $str =~ s/\\([0-7]{1,3})/oct2char($1)/eg;
+    $str =~ s/\\x([0-9a-fA-F]{1,2})/hex2char($1)/eg;
     return $str;
 }