If you used warnings, Perl would tell you what goes wrong:

> perl -we "my $filename = qq(d:\Swalpa Development kaliri ....Sir\Wor
+kSpace\Perl\CMD_File.txt);"
Unrecognized escape \S passed through at -e line 1.
Unrecognized escape \W passed through at -e line 1.
Unrecognized escape \P passed through at -e line 1.
Unrecognized escape \C passed through at -e line 1.
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A backslash is a special character in (double-quoted) strings. See perlop.