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

sub myrun{
...}
my $run = $condition ? 'system' : 'myrun';

[download]

$run @args; or eval {$run @args} did not work like bash do

what's the trick perl use about this?

Replies are listed 'Best First'.
Re: how to assign 'system' to a value, and eval it.
by hippo (Archbishop) on Jun 09, 2024 at 16:33 UTC

    Sounds like a job for coderefs.

    #!/usr/bin/env perl
use strict;
use warnings;

sub myrun {
    print "Yeah, just printing @_\n";
}

sub mysystem {
    system @_;
}

for (0..6) {
    my $run = $_ % 2 ? \&mysystem : \&myrun;
    $run->("echo Number $_");
}

    [download]
    did not work like bash do

    You'll have to give more detail here. An SSCCE would be good.

    🦛

[reply]
[d/l]

      And the google fodder you're (the OP) probably going to want next is "dispatch table".

      The cake is a lie.
      The cake is a lie.
      The cake is a lie.

[reply]
      yeah, thank you.that's the way I want.now I realized the necessity of using reffed subroutine. 
      my %run = (x => \&system, X => \&myrun);
my ($run, @args);
foreach(@ARGV){
if (/^-([xX])$/){
   $run = $run{$1}
}elsif (/^-/){
   push @args, $_
}
$run->(@args)

      [download]
      It's using prepared hash to switch run command, that's the logical way instead of using 'if ($run eq 'x'){system ...}', the ugly way I tried to avoid.
[reply]
[d/l]

        Consider using Getopt::Long instead of hand-rolling your option parsing. Getopt::Long can also set up your callbacks but will handle many more features:

        use Getopt::Long qw(:config pass_through);
my $run;
GetOptions(
    'x|run-using-system'   => sub { $run = \&system },
    'X|run-using-mysystem' => sub { $run = \&mysystem },
);
$run->(@ARGV);

        [download]
[reply]
[d/l]
Re: how to assign 'system' to a value, and eval it.
by soonix (Chancellor) on Jun 09, 2024 at 15:52 UTC
    consider the difference between 
    'system'($whatever);
'myrun'($whatever);

    [download]
    and 
    system($whatever);
myrun($whatever);

    [download]
    • $system is a variable (as you know)
    • system is a function
    • 'system' is a string
[reply]
[d/l]
[select]
      yeah, perl did not try to '$command xxx' like bash do. that's a good behavior.
[reply]
Re: how to assign 'system' to a value, and eval it.
by harangzsolt33 (Deacon) on Jun 09, 2024 at 21:02 UTC
    Personally, I would avoid using eval, but if you're going to use eval, you might as well do it this way: 

    #!/usr/bin/perl -w

use strict;
use warnings;

my $condition = 0;

sub RunProg   # Run program only if it exists
{
  my $CMD = join(' ', @_);
  my $PRG = ($CMD =~ m/^([a-zA-Z0-9_\/\-.~!]+)/) ? $1 : '';
  if (length(`which $PRG`)) { return system("$CMD"); }
  return -1;
}

my @args = ('yad --help');

my $RET = eval(($condition ? 'system' : 'RunProg') . '(@args);' );
print "\nRETURN VALUE = $RET\n";

    [download]
[reply]
[d/l]
        if (length(`which $PRG`))

      Use the core module IPC::Cmd for increased portability and functionality: 

      use IPC::Cmd 'can_run';

my $path = can_run($PRG);

      [download]
[reply]
[d/l]
        I don't know IPC has it.
[reply]
      That helps too.
[reply]

Back to Seekers of Perl Wisdom