Finally!!!! it was the space which was creating problem thanks guys below trick is helpful, 
p  "==$string_variable=="

[download]
now I change my ch_dir function to this, 
       my ($cmd,$patch,$step) = @_;
        $cmd =~ s/\s*cd\s* //;
         chdir($cmd) || die

[download]
Cheers!!!

In reply to Re^2: Updates problem with single quote by Sun751
in thread Updates problem with single quote by Sun751

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