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

Hi there , can someone tell me how to pass an array to a script as an argument: I am calling another perl script from my perl script and passing it an array as an argument : 
 
#in my calling script
system(qq(perl script2.pl @theArray));

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#in my reciving script
my @RecivedArray;
if ($#ARGV != 0)
{
die " no argument was passed\n";
}
@RecivedArray = $ARGV[0];

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Can someone tell me what is the problem of the way I am passing the array? thanks

Replies are listed 'Best First'.
Re: Passing arguments
by John M. Dlugosz (Monsignor) on Jan 28, 2004 at 21:50 UTC
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Re: Passing arguments
by Roy Johnson (Monsignor) on Jan 28, 2004 at 22:09 UTC
    First, bypass any shell interpolatation to keep your array elements separate in transit: 
    system('perl', 'script2.pl', @theArray);

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    Then, your second script can just use @ARGV: 
    @ReceivedArray = @ARGV;

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    The PerlMonk tr/// Advocate
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Re: Passing arguments
by Zaxo (Archbishop) on Jan 28, 2004 at 21:56 UTC

    This logic is probably wrong: 

    if ($#ARGV != 0) {
    die " no argument was passed\n";
}

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    I think you want to test equality, and the 0 may be wrong. It might help sort this out if you eliminated the shell by calling the list form of system and checking errors, system( '/path/to/perl', '/path/to/script2.pl', @theArray) and die $?, $!;

    After Compline,
    Zaxo

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Re: Passing arguments
by blue_cowdawg (Monsignor) on Jan 28, 2004 at 21:57 UTC

        Can someone tell me what is the problem of the way I am passing the array?

    Check out this experiment: 

    $ cat argvtest.pl
printf "I saw %d arguments\n",$#ARGV+1; #show how many
@argsin=@ARGV; # Snarf in the argnuments
 
printf "They were \"%s\"\n",join(",",@argsin); # and what

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    a test run shows: 
    $ perl argvtest.pl 1 2 3 4
I saw 4 arguments

They were "1,2,3,4"

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     $#ARGV is the argument count minus one or in other words the last index of the array @ARGV or the list of arguments passed to the script.

    With that in mind your test should look something like: 

    if ( $#ARGV < 0 ) { # NOTE: not != 0 
    printf "I expected an argument not simple refutation\n";
    exit(0);
}

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    UPDATE: Re-reading your original post I picked up on something...

    You tried: 

    @RecievedArray=$ARGV[0];

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    Since @ARGV is an array of scalars you are just referencing the first element of @ARGV which is itself a scalar and attempting to assign that to an array.

    I set up another experiment just to demonstrate what is going on: 

    use Data::Dumper;
 
@ry=qw/ a b c d /;
@ry2=$ry[0];
 
printf "First array:\n";
print Dumper(\@ry);
 
printf "Second array:\n";
print Dumper(\@ry2);

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    When that code is run you get the following: 
    First array:
$VAR1 = [
          'a',
          'b',
          'c',
          'd'
        ];
Second array:
$VAR1 = [
          'a'
        ];

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    As you can see all that gets assigned to the second array is the first element of the first array.

    Hope all this helps.

    Peter L. Berghold -- Unix Professional
    Peter at Berghold dot Net
       Dog trainer, dog agility exhibitor, brewer of fine Belgian style ales. Happiness is a warm, tired, contented dog curled up at your side and a good Belgian ale in your chalice.
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Re: Passing arguments
by monktim (Friar) on Jan 28, 2004 at 21:53 UTC 
    #in my calling script
my @array = ('a','b','c');
system(qq(perl C:\\script2.pl @array));
print "system failed.  [$?]: $!" if ($?);

#if args contain spaces
my @array = ('a 1','b 2','c 3');
my $args;
$args .= '"'.$_.'" ' foreach (@array);
system(qq/perl C:\\Backup\\script2.pl $args/);
print "system failed.  [$?]: $!" if ($?);

# Script2.pl
my @RecivedArray = @ARGV;;
print join(',',@RecivedArray);

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    Update Added a line of code to check the status of the system call. Also added a block showing arguments that contain spaces.
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Re: Passing arguments
by revdiablo (Prior) on Jan 28, 2004 at 21:59 UTC

    To generalize your question, you are looking for a method of Inter-Process Communication. There are many ways to do this, from your method (command line arguments), to a simple text file, to a full blown client-server arrangement. The type of IPC one uses depends on the situation at hand. For lots of documentation on the subject, check out perldoc perlipc.

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Re: Passing arguments
by NetWallah (Canon) on Jan 29, 2004 at 05:50 UTC
    As others have suggested, there are several hazards you will encounter when trying to pass parameters using the shell (system call).

    Some of these are:

    • Spaces in data
    • Binary data
    • structured data (AoA or HoA etc)
    • Special chars in data like < ^ >

    For a more general solution, you may want to consider using the storable Module, which can be used thus: 

        #In Calling program
    use Storable; 
    store(\@array, "filename");

    # later , in Called program ..
    $aref = retrieve("filename");         # Get a ref or
    @array = @{ retrieve("filename") };   # direct into array

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    "When you are faced with a dilemma, might as well make dilemmanade. "
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Re: Passing arguments
by ysth (Canon) on Jan 28, 2004 at 21:55 UTC
    $#ARGV is the last used index in @ARGV. If @ARGV contains 1 element, $#ARGV will be zero. It's -1 if @ARGV is empty. You should use if (@ARGV) instead.
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