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

hello wise ones

i had a strange Perl idea but i can get it works: i want a program that can transform itself into another thing on given argouments.
I would like to use it alone:
   me.pl --execute  --key sum
or in a pipeline, like in:
   echo '1 2 3' | me.pl --execute  --key sum | cat

I' m using Getopt::Long as it can grab options that i need in the main program, and can also leave other things in @ARGV..
The below code only works in the case c and not in pipeline:
   me.pl --execute  --key c 1 2 3
Any suggestion or explication are welcome

thanks
L* 

#!/usr/bin/perl
use warnings;
use strict;
use Getopt::Long;

my ( $execute, $key);

GetOptions (
            "key=s"   => \$key,
            "execute"  => \$execute)||die;

my %cmds = ( a => sub {exec 'perl -e "print map {qq!\t$_\n!}"',@_ },
             b => sub {exec 'perl -e "$|++;print qq(ee r r );sleep 5"'
+},
             c => sub {my $res; foreach (@ARGV) {$res+=$_}; print $res
+;exit 0 },


);

if ($execute && exists $cmds{$key} )  {
    print "ole\n";
    $cmds{$key}->(@ARGV);

}
# theoretically never here ..
print "still in \@ARGV: ", (join("|",@ARGV),"\n");

[download]
UPDATE:
on ikegami suggestion i add what i'm getting on tests: echo 1 2 3 | code-dispatch.pl --execute --key c gives something like:"the process proved to write in an unexisting pipe"
ole

Use of uninitialized value $res in print at c:\SCRIPTS\code-dispatch.pl line 14.

echo 1 2 3 | code-dispatch.pl --execute --key a prints:
ole
c:\SCRIPTS>syntax error at -e line 1, at EOF
Execution of -e aborted due to compilation errors.
and program hangs..

L*
there are no rules, there are no thumbs..

Replies are listed 'Best First'.
Re: become another via exec in dispatch table
by ikegami (Patriarch) on Jan 31, 2012 at 10:29 UTC 
    exec 'perl -e "print map {qq!\t$_\n!}"',@_

    [download]

    will fail with ENOENT (No such file or directory) when @_ isn't empty. When using the multiple argument form of exec the first argument is to be the program to execute. There's no file named perl -e "print map {qq!\t$_\n!}", much less a program.

    And when @_ is empty, you have a different problem. perl will run, but the shell will have replaced $_ with something else due to improper quoting.

    The solution to both is: 

    exec 'perl', '-e', 'print map {qq!\t$_\n!}', @_

    [download]

    Are these the problems you were asking about?

    PS — If you had a problem with exec, you should have checked what error exec returned.

[reply]
[d/l]
[select]
      sorry may be i do not explicate well my idea: i changed the b k key of dispatch table as suggested by ikegami:
      b => sub {exec 'perl', '-e', 'print map {qq!\t$_\n!}', @_},

      [download]

      but does not work alone like in:
      code-dispatch.pl --execute --key b   a a a
      nor in pipeline, like:
      echo 1 2 3 | code-dispatch.pl --execute --key b

      theese line only print 'ole' (the check if that key exists in the table) and do not print a column of argouments as intended to do (by me)

      thanks

      there are no rules, there are no thumbs..
[reply]
[d/l]
[select]

        Again, "does not work" is not an adequate description. Specifically, you get: 

        ole
syntax error at -e line 1, at EOF
Execution of -e aborted due to compilation errors.

        [download]

        So lets look at the code: 

        print map {qq!\t$_\n!}

        [download]

        Where's map's list of values?

[reply]
[d/l]
[select]
Re: become another via exec in dispatch table
by ikegami (Patriarch) on Jan 31, 2012 at 10:23 UTC
    You didn't specify what it does wrong and what it should be doing instead.
[reply]

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