http://qs1969.pair.com?node_id=627120


in reply to tar, system() & pipes?

The > /tmp/file is a *shell* directive, but the shell is not invoked when you use system LIST instead of system EXPR. You're passing > and /tmp/file as arguments to tar, and tar doesn't know what to do with them.

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Re^2: tar, system() & pipes?
by Anonymous Monk on Jul 17, 2007 at 20:35 UTC

    Thank you for your reply.

    So there isn't a way to spawn piped commands from within a Perl script?

[reply]

      I think the following is safe on unix platforms: 

      my $q_archive  = quotemeta($ARGV[0]);
my $q_filename = quotemeta($filename);
system("tar $args $q_archive > $q_filename")

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      It can also be written as 

      system("tar $args \Q$ARGV[0]\E > \Q$filename\E")

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      quotemeta (called directly or via \Q..\E) will backslash-escape any non-word characters, so the file names can safely contain symbols and spaces.

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        Thank you! Use of quotemeta appears to work.

        Why is this needed?
[reply]

      If the intention is to read the output file back into your program once tar is finished, you could bypass the filesystem by using a piped-open:

      (See the docs for perlfuncopen and perlopentut) 

      # ..................v  
open TAR, "tar .... |" or die ...;
while( <TAR> {
    ## do stuff with the tar output
}

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      ## do stuff with the tar output could be as simple as print FILE $_;.

      See also IO::Pipe.

      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
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