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FAQ 5.5 How can I copy a file?
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FAQ 5.5 How can I copy a file? PerlFAQ Server 06-07-2008
Posted by PerlFAQ Server on June 7, 2008, 3:03 pm
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 This is an excerpt from the latest version perlfaq5.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

--------------------------------------------------------------------

5.5: How can I copy a file?


(contributed by brian d foy)

Use the File::Copy module. It comes with Perl and can do a true copy
across file systems, and it does its magic in a portable fashion.

use File::Copy;

copy( $original, $new_copy ) or die "Copy failed: $!";

If you can't use File::Copy, you'll have to do the work yourself: open
the original file, open the destination file, then print to the
destination file as you read the original.



--------------------------------------------------------------------

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Posted by Bill H on June 8, 2008, 7:01 am
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> This is an excerpt from the latest version perlfaq5.pod, which
> comes with the standard Perl distribution. These postings aim to
> reduce the number of repeated questions as well as allow the community
> to review and update the answers. The latest version of the complete
> perlfaq is athttp://faq.perl.org.
>
> --------------------------------------------------------------------
>
> 5.5: How can I copy a file?
>
> =A0 =A0 (contributed by brian d foy)
>
> =A0 =A0 Use the File::Copy module. It comes with Perl and can do a true co=
py
> =A0 =A0 across file systems, and it does its magic in a portable fashion.
>
> =A0 =A0 =A0 =A0 =A0 =A0 use File::Copy;
>
> =A0 =A0 =A0 =A0 =A0 =A0 copy( $original, $new_copy ) or die "Copy failed: =
$!";
>
> =A0 =A0 If you can't use File::Copy, you'll have to do the work yourself: =
open
> =A0 =A0 the original file, open the destination file, then print to the
> =A0 =A0 destination file as you read the original.

What is the advantage of using this over using system("cp $original
$new_copy"); (or system("copy $original $new_copy"); on windows)? Is
it faster or is it just "perlish"? Or am I missing something obvious?

Bill H

PS When did Google Groups drop the captcha?

Posted by Jürgen Exner on June 8, 2008, 9:28 am
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>>     Use the File::Copy module. It comes with Perl and can do a true copy
>
>What is the advantage of using this over using system("cp $original
>$new_copy"); (or system("copy $original $new_copy"); on windows)? Is
>it faster or is it just "perlish"? Or am I missing something obvious?

system() isn't portable.
File::Copy also avoids forking external processes, although the time
savings are probably pretty irrelevant given the nature of the
operation.

jue

Posted by Peter J. Holzer on June 8, 2008, 10:15 am
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>> 5.5: How can I copy a file?
>>
>>     (contributed by brian d foy)
>>
>>     Use the File::Copy module. It comes with Perl and can do a true copy
>>     across file systems, and it does its magic in a portable fashion.
>>
>>             use File::Copy;
>>
>>             copy( $original, $new_copy ) or die "Copy failed: $!";
>>
>>     If you can't use File::Copy, you'll have to do the work yourself: open
>>     the original file, open the destination file, then print to the
>>     destination file as you read the original.
>
> What is the advantage of using this over using system("cp $original
> $new_copy"); (or system("copy $original $new_copy"); on windows)?

I think you just answered your question: The advantage is that you can
just write

copy( $original, $new_copy )

instead of

if (os_is_some_kind_of_unix()) {
        system("cp", $original, $new_copy);
} elsif (os_is_windows()) {
        system("copy", $original, $new_copy);
} else {
        ...
}

and wonder how you can write sub os_is_some_kind_of_unix.

(and you won't make stupid mistakes like system("cp $original
$new_copy"). which won't work if either $original or $new_copy contains
any of a large number of "dangerous" characters)

OTOH, when you use a system-specific tool like "cp", you can do
system-specific things, like preserve permissions or timestamps.


> Is it faster

It is probably faster for small files. It also is more robust (even if
the system has a "cp" command, it may not be in your path).

> or is it just "perlish"?

That, too.

        hp


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