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System() or the like

by PyroX (Pilgrim)
on Sep 18, 2001 at 02:06 UTC ( #112985=perlquestion: print w/replies, xml ) Need Help??

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

Is there ANY solution to get the text output from system()?

For example:
$run="snmpwalk $host $opt_c ifType.".$thisport; $type=system($run); print "$MAC $type $ifName $vlan $host\n";
As you can see, I want to return the result of an snmp walk, IN A VARIABLE. It obviously returns the results instantly, but I need it in a var, so I can work with it.

Edit kudra, 2001-09-18 Added code tags

Replies are listed 'Best First'.
Re: System() or the like
by blakem (Monsignor) on Sep 18, 2001 at 02:10 UTC
    You can use the backticks (like the apostrophe, but slanted the other way... usually found next to the !/1 key) to capture the output of another process....
    $run="snmpwalk $host $opt_c ifType.".$thisport; $type=`$run`; print "$MAC $type $ifName $vlan $host\n";


Re: System() or the like (code)
by deprecated (Priest) on Sep 18, 2001 at 02:48 UTC
    Um, I am surprised nobody has mentioned qx//. I tend to prefer qx{ foo } over backticks because it is much easier to see at high resolution.

    Also, several shell programming books I have read say that the use of backticks is, er, deprecated. They prefer to use $(), which qx{} somewhat resembles.

    Just my too sense.

    brother dep

    Laziness, Impatience, Hubris, and Generosity.

      I've not heard that Perl's backticks are deprecated. The $() syntax is a ksh feature, which by the way nests very easily, and is not available in sh. I don't agree that $() looks like qx{} but regardless agree that it's a more elegant solution.
Re: System() or the like
by geektron (Curate) on Sep 18, 2001 at 03:17 UTC
    If you're using, there's already a method for doing this:

    From the cpan documentation:

    get_table() - retrieve a table from the remote agent Blocking $response = $session->get_table($oid); Non-blocking $ok = $session->get_table( -baseoid => $oid, [-callback => sub {},] [-delay => $seconds] );
    it might be best to use a module here rather than depending on system commands and/ or backticks.

    i do a fair to large amount of SNMP work at work, and I use for most, if not all, apps that need this kind of info.

      Just to avoid confusion, I think you mean Net::SNMP.
Re: System() or the like
by maverick (Curate) on Sep 18, 2001 at 02:13 UTC
    Try opening the command to a pipe.
    open(PIPE,"$run |") || die "pipe open failed: $!"; while(<PIPE>) { print $_; } close(PIPE);

    perl -l -e "eval pack('h*','072796e6470272f2c5f2c5166756279636b672');"

Re: System() or the like
by VSarkiss (Monsignor) on Sep 18, 2001 at 02:12 UTC

    Use backticks:

    $run="snmpwalk $host $opt_c ifType.".$thisport; $type=`$run`; print "$MAC $type $ifName $vlan $host\n";

    More information at perlfunc:system; in particular, the second paragraph.


Re: System() or the like
by howie (Sexton) on Sep 18, 2001 at 03:13 UTC
    either $type=`$run`; (those are backticks, not quotes) or
    open(OUTPUT,"$run|"); $type=<OUTPUT>; close(OUTPUT);
    should do it. Both are in the 'Social Perl' chapter of the camel book, IIRC.
Re: System() or the like
by cider (Acolyte) on Sep 18, 2001 at 12:57 UTC


    I present thee with hoho_system(), it can be called with the silent option below to not additionally display output to stdout:

  • $type = hoho_system("$run", "silent");

    Or, it can also be noisy, and may be executed like so:

  • $type = hoho_system("$run");

    And for bonus points, I have included support for an optional global $logfile variable, which can be declared as the following optionally:

  • $logfile = "some_file_that_exists";

    # on with the show,

    sub hoho_system { my ($cmd, $option) = @_; my ($returned_result); my $silent = 0; if ( defined($option) ) { if ( $option =~ m/silent/ ) { $silent = 1 +; } } if ( defined($logfile) ) { open LOG, "+>> $logfile"; print LOG "$cm +d: $_\n"; } open CMD, "$cmd |" or die "failure running $cmd: $!\n"; while(<CMD>) { print unless $silent; print LOG "$_"; $returned_result = "$_\n$returned_result"; } close CMD; if ( defined($logfile) ) { close LOG; } return $returned_result; }

    Using arrays instead of scalars in multi-line responses would be advisable, and for such you may change the $returned_result references to @returned_result, and change the $returned_result assignment line to push @returned_result, "$_";

    busunsl: switched pre tag to code tag. htmlism.

      Sorry to spoil that, but I think if you present a solution, it should work:

      running it gives me:

      syntax error at C:\WINNT\Profiles\int5398\src\test\ line 9, near +"if $option " syntax error at C:\WINNT\Profiles\int5398\src\test\ line 19, near + "}"
      The line while () { starts an endless loop.

      $returned_result will be empty.

      And even if it would contain something, it would be in reverse order.

      Please test your code before posting.

DONE: System() or the like
by PyroX (Pilgrim) on Sep 18, 2001 at 20:27 UTC
    Thanks guys,
    It looks like this will work the best for me, thank you everyone.
    $run="snmpwalk $host $opt_c ifType.".$thisport; open(PIPE,"$run |") || die "Failed to get type, stopped."; while(<PIPE>) { $type=$_; } close(PIPE); print "$MAC $type $ifName $iftomodule{$ifIndex} $iftopor +t{$ifIndex} $ifIndex $bridgeport $vlan $host\n";

    Edit kudra, 2001-09-19 Added code tags

      Thank you soooooo much this help a ton! $run="dir.".$thisport; open(PIPE,"$run |") || die "Failed to get type, stopped."; while(<PIPE>) { $type=$_; print($type); } close(PIPE);

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