I just wanted to know what does this code do?
my $string_1 = "foo bar";
my $val = 3;
if($string_1) {
}
basically what happen if you just use a variable inside an if statement?
thanks
It checks if the value of the variable is true. In Perl, everything is true but the following:
0 and the string '0'
undef
() (the empty list)
'' (an empty string)
This is documented in perlsyn. It also works with any other kind of value. You can also put a string, a function call inside the if condition. The behavior is always the same.
this will check variable '$string' has not null value
Related
I have a hash defined as below:
Hash[String, String] $hashtest = { "abc" => "test1", "xyz" => "test2" },
I have String variable, I need to search for the given key in the hash and if a value is found, I need to assign that value to the variable "result" otherwise I need to assign a default value "test". How can I do this is in puppet? Or only way to do this is using if else condition?
It should be similar like this, but the below code is not working. Kindly correct me what I'm doing wrong.
String $variable = $hashtest[$key] ? { true => $hashtest[$key], false => "test" },
It would be really helpful if someone helps me with this thanks in advance.
I am assuming in your pseudocode you are intending to assign a value with a return from a selector, and not also providing a pseudocode for a ternary-like expression in Puppet. With that in mind, we can achieve this with something similar to Python:
String $variable = $key in $hashtest ? {
true => $hashtest[$key]
false => "test"
}
Note that prior to Puppet 4 you would need the has_key? function (analogous to has_key Hash method in Ruby) from stdlib:
String $variable = has_key($hashtest, $key) ? {
true => $hashtest[$key]
false => 'test'
}
In stdlib there is also a function roughly equivalent to a "null coalescing" operator in other languages (null being roughly equivalent to undef type in Puppet and nil in Ruby) that would provide a cleaner expression:
String $variable = pick($hashtest[$key], 'test')
Similar to the coalescing patterns in other languages, pick will return the first argument that is not undef or empty.
As well as matts answer you can also use the following
$variable = $hashtest[$key].lest || { 'test' }
$variable = ($key in $hashtest).bool2str($hashtest[$key], 'test')
$variable = $hashtest.has_key($key).bool2str($hashtest[$key], 'test')
All of these options are missing the most simple and powerful option that's been available from the core library since puppet 6; the get function.
The get function allows you specify a dot separated path of nested keys to look up as the first argument, and a default value for the second. By default, it will return undef if a value cannot be found, making it ideal for use in conditional expressions since undef is the only value in puppet that automatically converts to false. You can even pass a lambda to it to handle missing values.
In your case, the answer is as simple as $variable = $hashtest.get($key, 'test') or $variable = get($hashtest, $key, 'test'), though I personally find the first option easier to read.
How it will look this using preg_replace_callback?
$str = preg_replace('/\&\#([0-9]+)\;/me', "code2utf('\\1',{$lo})", $str);
If I am not mistaken you want to use preg_replace_callback instead of using the /e modifier.
If you want to pass extra parameters to the callback function you could make use of the use indentifier or wrap the callback in another function.
The second example could look like:
$str = preg_replace_callback(
'/\&\#([0-9]+)\;/m', function ($matches) use ($lo) {
// function body with return statement
}, $str
);
Notes
Your regex \&\#([0-9]+)\; will match a string like 𸽡. I think you don't have to ecape the & and #.
In your code you use return strtoupper($matches[1], $lo); but strtoupper takes one parameter instead of 2 parameters.
If this is what you want to match, then when running your code you could see that $matches[1] contains "233333" so this will be called return strtoupper("233333");
Getting some odd behaviour in a Perl script that I don't quite understand. I'm trying to make some of my magic string literals into variables that can be modified more easily.
I have an argument in my subprocedure called $in_feature. Right now it's value is simply "in_feature". I can print it out and it looks fine. So far so good...
This code fails, though:
if ($in_feature != "" && !$blockModel->is_field($in_feature))
{
print "ERROR: was expecting to find a variable in the block model called $in_feature.\n";
return;
}
If I remove the string comparison and change the method call back to the string literal it works as expected.
if (!$blockModel->is_field("in_feature"))
{
print "ERROR: was expecting to find a variable in the block model called $in_feature.\n";
return;
}
So the variable is somehow a string, that is equal to empty string, and can't be used in place of a string?!? Why's this?
String comparison in perl uses ne and eq instead of != and ==
Replace $in_feature != "" with $in_feature ne "" and it might fix your issues.
Why does this statement,
if (! $ssh_options{user}) {
delete $ssh_options{user};
}
return true, but this statement
if ($ssh_options{user} eq 'undef') {
delete $ssh_options{user};
}
give me the error,
Use of uninitialized value $ssh_options{"user"} in string eq at analyze.pl line 230.
I thought you always had to have something for perl to compare the value of the variable being compared.
** Update **
# Quick Joe Smith
I cannot base my comparison on whether the hash keys exist or not because the values for this hash
sub ssh_connect {
my $host = shift;
my %ssh_options = (
port => shift,
user => shift,
password => shift
);
Come from this function which calls the sub routine
if ((exists $config_file{user}) && (exists $config_file{password})) {
my $vmware_user = $config_file{user};
my $vmware_password = $config_file{password};
ssh_connect($vmware_host, $vmware_port, $vmware_user, $vmware_password);
} else {
ssh_connect($vmware_host, $vmware_port);
}
Perl hash slots have a number of ways they can be false. If the key has never been filled, the exists function will return false. If the key exists but contains an undefined value, exists will be true but the defined function will return false. In normal boolean context, as given by an if statement, a hash key that was never filled, or is undefined, '', 0 or anything that reduces to those will be false.
From your update, it sounds like what you want is to use defined
delete $ssh_options{user} unless defined $ssh_options{user};
Use exists for checking hash keys.
if (exists $ssh_options{user}) {
...
}
However, in your case, it seems as though you're checking for existing keys whose values may be undefined, in which case:
if (defined $ssh_options{user}) {
...
}
The above may be what you want.
As a sidenote, checking to see if the value of any variable is defined in the way you described:
if ($something eq 'undef') {
...
}
Is wrong. You're checking to see if the variable contains the string "undef". What you need in those situations is:
unless (defined $something) {
...
}
But if $ssh_options{"user"} is uninitialized then it it doesn't have a value to compare to.
With Perl, undefined evaluates to false in Boolean context. So your first test 'works' as you expect. However, it might introduce a bug if zero or an empty string is a legitimate value for $ssh_options{user} to hold, if you don't wish to treat that the same as undef. That's because your first test doesn't differentiate between false as a value, and false as undefined. As far as Perl's Boolean evaluation goes, all of the following are "false": 0, '' (empty string), undef, or an empty list.
Your second snippet of code fails because undef should be a bareword, not a quoted string. 'undef' as a quoted string IS a value, which would actually evaluate to 'true' in Boolean tests. Because you're comparing an actual value to your hash element, Perl warns you that you're comparing something to an undefined value. In this case, the undefined value is $ssh_options{user}. It's actually good that Perl is warning you; it's given you a clue as to what you're doing wrong.
If you really want to test whether $ssh_options{user} is defined, use the defined() function. If you want to test whether $ssh_options{user} exists, use the exists() function.
The following script gives me what I want but Perl also throws me a warning saying "Useless use of a variable in void context". What does it mean?
use strict;
use warnings;
my $example = 'http\u003a//main\u002egslb\u002eku6\u002ecom/c0/q7LmJPfV4DfXeTYf/1260269522170/93456c39545857a15244971e35fba83a/1279582254980/v632/6/28/a14UAJ0CeSyi3UTEvBUyMuBxg\u002ef4v\u002chttp\u003a//main\u002egslb\u002eku6\u002ecom/c1/q7LmJPfV4DfXeTYf/1260269522170/3cb143612a0050335c0d44077a869fc0/1279582254980/v642/10/20/7xo2MJ4tTtiiTOUjEpCJaByg\u002ef4v\u002chttp\u003a//main\u002egslb\u002eku6\u002ecom/c2/q7LmJPfV4DfXeTYf/1260269522170/799955b45c8c32c955564ff9bc3259ea/1279582254980/v652/32/4/6pzkCf4iqTSUVElUA5A3PpMAoA\u002ef4v\u002chttp\u003a//main\u002egslb\u002eku6\u002ecom/c3/q7LmJPfV4DfXeTYf/1260269522170/cebbb619dc61b3eabcdb839d4c2a4402/1279582254980/v567/36/19/MBcbnWwkSJu46UoYCabpvArA\u002ef4v\u002chttp\u003a//main\u002egslb\u002eku6\u002ecom/c4/q7LmJPfV4DfXeTYf/1260269522170/1365c39355424974dbbe4ae8950f0e73/1279582254980/v575/17/15/EDczAa0GTjuhppapCLFjtaQ\u002ef4v';
my #raw_url = $example =~ m{(http\\u003a.+?f4v)}g;
my #processed_url = map {
s{\\u003a}{:}g,$_;
s{\\u002e}{.}g,$_;
s{\\u002d}{#}g,$_;
} #raw_url;
print join("\n",#processed_url);
And why this map thing doesn't work if I omit those dollar underscores like so?
my #processed_url = map {
s{\\u003a}{:}g;
s{\\u002e}{.}g;
s{\\u002d}{#}g;
} #raw_url;
When I omit those dollar underscores, I get nothing except for a possibly success flag "1". What am I missing? Any ideas? Thanks like always :)
What you want is...
my #processed_url = map {
s{\\u003a}{:}g;
s{\\u002e}{.}g;
s{\\u002d}{#}g;
$_;
} #raw_url;
A map block returns the value composed of the last statement evaluated as its result. Thats why we pass the $_ as the last statement. The substitution operator s{}{} returns the number of substitutions made.
In your prior setup, you had by itself the following statement. Which is pretty much meaningless and that is what Perl is warning about.
s{\\u003a}{:}g, $_;
You already have the answer you were looking for, but I wanted to point out a subtlety about using the substitution operator inside a map block: your original array is also being modified. If you want to preserve the original array, one way to do it is to make a copy of the array, then modify only the copy:
my #processed_url = #raw_url;
for (#processed_url) {
s{\\u003a}{:}g;
s{\\u002e}{.}g;
s{\\u002d}{#}g;
}
Or, if you only need one array, and you want the original to be modified:
for (#raw_url) {
s{\\u003a}{:}g;
s{\\u002e}{.}g;
s{\\u002d}{#}g;
}