in reply to a small doubt

See system. It returns the exit code, which is traditionally 0 for success, opposite to how open returns success. For clearer code, I'd use 
if (0 != ($rc = system 'cp', '-p', $file, $back)) {
    unixerr_function('CP', 'file', 'Partial file may have been copied.
+');
}

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Re^2: a small doubt
by sandy105 (Scribe) on Nov 11, 2014 at 10:16 UTC

    thanks , thats what i wanted to know

[reply]

      Generally speaking, most built-in Perl functions return a value which indicates success, with a non-true value indicating failure (zero, empty string, or undef). Many user-written Perl functions follow the same convention.

      System commands in Unix, Windows, etc., will result in a numeric exit value indicating an error, with zero indicating no error.

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