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loop inside system command

by DS (Acolyte)
on Jul 17, 2002 at 13:58 UTC ( [id://182428]=perlquestion: print w/replies, xml ) Need Help??

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

Hello , I am using the system command to excute a command inside my script , however I am trying to use an array inside that system command ,,, forexmaple , the command line is : 
my $firstbuild = hi.bld
my @otherbuilds = q( low.bld hello.bld cow.bld ); 
system(qq(C:/execu $firstbuild @otherbuilds file.c));

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knowing that the array @otherbuilds could have more or less builds than three. so I am trying to find a way to do somthing like this 
system(qq(C:/execu $firstbuild low.bld hello.bld cow.bld file.c));

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somehow read the array index and list them in an order .. I tried a loop within that command but system didn't like it . what do yall think .. thanks for hints

Replies are listed 'Best First'.
Re: loop inside system command
by stephen (Priest) on Jul 17, 2002 at 14:14 UTC
    I'd recommend using the multi-argument variant of system(). 
    system("C:\\execu", $firstbuild, @otherbuilds, 'file.c')
   and die "System command failed";

    [download]

    stephen

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[d/l]
Re: loop inside system command
by abaxaba (Hermit) on Jul 17, 2002 at 14:18 UTC
    If I understand your question correctly, you'll need to execute system singularly, and build your loop around it, as opposed to in it 
    foreach ($firstbuild, @otherbuilds)
{
    system (qq(C:/execu $_ file.c));
}

    [download]
    One thing you may consider, esp. if @otherbuilds can grow to be sufficiently large: system is a double fork, in terms of processes spawned. One proc. for the system call, one for the actual command to run. If you're going to be calling system on more than a couple of items, you may consider doing something like so: 
    open (OUT, ">cmd.txt") || die "$!\n";
foreach ($firstbuild, @otherbuilds)
{
    print OUT "C:/execu $_ file.c\n";
}
close OUT;
system ("cmd.txt");

    [download]
    The reason? Instead of spawning 2N processes, you'll spawn only N+1. 3 or 4 system calls probably doesn't warrant the extra work. If you got 100 or so...well, you get the picture.

    ÅßÅ×ÅßÅ
    "It is a very mixed blessing to be brought back from the dead." -- Kurt Vonnegut
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[d/l]
[select]
      thanks to you all :)
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Re: loop inside system command
by cidaris (Friar) on Jul 17, 2002 at 14:18 UTC
    I got this to work: 
    my $command_line = "";
my $first_build = "hi.bld";
my @other_builds = qw( low.bld hello.bld cow.bld );
$command_line = "c:\\execu $first_build";
$command_line .= " " . shift @other_builds while (@other_builds);
$command_line .= " file.c";
print "$command_line\n";
system "$command_line\n";

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    Hope it helps.
    cidaris
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[d/l]
      Interesting, cidaris. But have you ever used the join command?

      It would save you your loop on "while(@other_builds)". 

      $command_line = "c:\\execu $first_build "; # note trailing space
$command_line .= join " ", @other_builds;
$command_line .= " file.c";

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      The only downside here is that you wind up with 2 spaces between $first_build and file.c if there are no other_builds.

      The problem goes away if you do everything in a join: 

      $command_line .= join " ", ("c:\\execu $first_build",@other_builds,"fi
+le.c");

      [download]

      --
      Mike
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[d/l]
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