How to properly call a sub by referencing in Perl - perl

Question

I'm working on a dispatching script. It takes a string with a command, does some cooking to it, and then parses it. But I can't grab a hold into the referencing:
Use::strict;
Use:warnings;
my($contexto, $cmd, $target, $ultpos, #params);
my $do = "echo5 sample string that says stuff ";
$target = "";
$cmd = "";
$_ = "";
# I do some cumbersome string parsing to get the array with
# the exploded string and then call parsear(#command)
sub parsear {
my %operations = (
'echo' => \&echo,
'status' => \&status,
'echo5' => \&echo5,
);
my $op = $_[0];
if ($operations{$op}){
$operations{$op}->(#_);
print "it exists\n";
}
else{
print "incorrect command.\n";
}
}
sub status {
print "correct status.\n";
}
sub echo {
shift(#_);
print join(' ',#_) . "\n";
}
sub echo5 {
shift(#_);
print join(' ',#_) . "\n" x 5;
}
I don't really know what the problem is. If the sub does not exist, it never says "incorrect command", and if I call for example "echo5 hello" it should print out:
hello
hello
hello
hello
hello
But it does nothing.
And when I call echo, it works as expected. What is the explanation?
Note: I'm on the latest version of Strawberry Perl

Answer 1

use strict; # 'use' is a keyword
use warnings;
# All these variables are not needed
sub parsear { # Learn to indent correctly
my %operations = (
'echo' => \&echo,
'status' => \&status,
'echo5' => \&echo5,
);
my $op = shift; # take first element off #_
if ($operations{$op}) {
print "$op exists\n"; # Make your status message useful
$operations{$op}->(#_);
} else {
print "incorrect command: $op\n"; # And your error message
}
}
sub status {
print "correct status.\n";
}
sub echo {
# shift(#_); # This is no longer needed, and now echo can be used as a
# normal subroutine as well as a dispatch target
print join(' ',#_) . "\n";
}
sub echo5 {
# shift(#_); # This is no longer needed
print +(join(' ',#_) . "\n") x 5; # Parentheses are needed since x binds tightly
}
Then running:
parsear 'status';
parsear 'echo', 'hello';
parsear 'echo5', 'hello';
parsear 'an error';
results in:
status exists
correct status.
echo exists
hello
echo5 exists
hello
hello
hello
hello
hello
incorrect command: an error
I am not sure what "cumbersome string parsing" you are doing since you did not include it, but if you are parsing a string like
my $do = "echo5 sample string that says stuff ";
where the command is the first word, and the arguments are the rest, you can either split everything:
parsear split /\s+/, $do;
Or use a regex to cut the first word off:
my ($cmd, $arg) = $do =~ /^(\w+)\s*(.*)/;
parsear $cmd => $arg;
You don’t even need the variables:
parsear $do =~ /^(\w+)\s*(.*)/;
Finally, the echo5 subroutine is a bit more complicated than it needs to be. It could be written as:
sub echo5 {
print "#_\n" x 5; # "#_" means join($", #_) and $" defaults to ' '
}

Answer 2

The x command binds differently from how you were expecting; you probably wanted:
print ((join(' ', #_) . "\n") x 5);
Both extra sets of parentheses seemed to be necessary.