Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

I am converting a bash script that executes many commands. Each
command logs the stderr and stdout to a file. I intended to use
the system command in Perl to the same effect. Here is a contrived
example to illustrate the problem I am running into.
Why does this not work? Why is >> having a problem?
my $logfile = '/tmp/zzzz';
`touch $logfile` if (!(-e($logfile)));

    if (system( "ls", 
                "-l",
                "/bin/bash",
                ">>",
                "$logfile",
                "2>&1"
              )) {
        print "Nope!\n";
    }

__END__

bash-2.05b$ perl a1.pl
ls: >>: No such file or directory
ls: 2>&1: No such file or directory
-rwxr-xr-x    1 root     root       598580 Sep 18  2003 /bin/bash
-rw-rw-r--    1 nooninmh man             0 Mar 29 18:52 /tmp/zzzz

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Re: system command has problem with '>>'
by JavaFan (Canon) on Mar 29, 2010 at 23:08 UTC
    If you call system with a list of arguments, no shell is involved. And it's the shell that interprets >>. Your way of calling system means ls is called, with >> as its third argument.

    Use: 

    unless (system "ls -l /bin/bash >> $logfile 2>&1") {
    print "Nope!\n";
}

    [download]
    instead.

    Further points: 1) there's no need to first create $logfile. The redirection will create it if necessary. 2) system returns 0 on success, following the Unix convention.

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Re: system command has problem with '>>'
by Anonymous Monk on Mar 29, 2010 at 23:09 UTC
    Its because you didnt read the documentation clearly. The ls program doesn't know what to do with >> or 2>&1, its not sh/csh/perl -V:sh

    Use systemx from IPC::System::Simple 

    use IPC::System::Simple qw[ systemx ]; ...

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      Not true. The shell processes '>>', not 'ls', as can be seen from the pastes below.
      Anyone else have any ideas on this?

      $ rm aa
      $ ls example_file.txt >> aa
      $ cat aa
      example_file.txt
      $ ls exam*
      example_file.txt
      $ ls example_file.txt >> aa
      $ cat aa
      example_file.txt
      example_file.txt
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        Not true. The shell processes '>>', not 'ls', as can be seen from the pastes below.

        Thats what I said.

        Anyone else have any ideas on this?

        Like I said, use IPC::System::Simple systemx, it process >> like the shell without invoking the shell, or like JavaFan said, invoke the shell

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