I have the following variables:
[string]$eth_netmask = "ext_netmask"
[string]$ext_netmask = "255.255.252.0"
$($eth_netmask) is returning ext_netmask. I was expecting 255.255.252.0
What am I doing wrong?
Thanks for the help in advance!
The command $eth_netmask returns the value of the variable named eth_netmask. The expression $(something) has nothing to do with variables, but instead evaluates the contents of the parentheses before evaluating the rest of the statement. That means that the statement $($eth_netmask) will evaluate in two steps:
1: $($eth_netmask) evaluates to the command "ext_netmask"
2: "ext_netmask" evaluates as a command which has the result of printing ext_netmask to the output.
This format is unnecessary since variables are normally resolved before the rest of the command anyway. My recommendation would be to avoid needing to do this at all if there is any alternative. Putting this kind of roundabout referencing into a piece of code can only cause problems. However, if you can't avoid it for some reason, it is possible to reference a variable the name of which is stored in another variable.
[string]$eth_netmask = "ext_netmask"
[string]$ext_netmask = "255.255.252.0"
Get-Variable -Name $eth_netmask -ValueOnly
This is the point at which the $(something) syntax becomes useful. If you need to use the value that you have just returned in another command, such as if the value was an ip that you were trying to ping, you might do something like this:
Test-Connection $(Get-Variable -Name $eth_netmask -ValueOnly)
Related
The problem here is that I do not understand well the difference between statements and blocks in control flow.
Looking the ternary operator I can use it to assign a variable. But this is an operator, so it is like applying a function--isn't it?
> my $variable = True ?? 34 !! 42;
34
since in the raku documentation says:
if documentation
if
To conditionally run a block of code, use an if followed by a
condition. The condition, an expression, will be evaluated immediately
after the statement before the if finishes. The block attached to the
condition will only be evaluated if the condition means True when
coerced to Bool. Unlike some languages the condition does not have to
be parenthesized, instead the { and } around the block are mandatory:
do documentation
do
The simplest way to run a block where it cannot be a stand-alone statement is by writing do before it:
so this should work in both cases:
> my $variable = do {34};
34
> my $variable = if True {34;} else {43;}
===SORRY!===
Word 'if' interpreted as a listop; please use 'do if' to introduce the statement control word
------> my $variable = if⏏ True {34;} else {43;}
Unexpected block in infix position (two terms in a row)
------> my $variable = if True⏏ {34;} else {43;}
as said in the error I need to add the do:
> my $variable = do if True {34;} else {43;}
34
So the if really does not run the block...or what is the real problem here?
TL;DR: The actual difference is between statement and expression, not statement and block. do is a statement prefix that creates expressions.
if actually creates a statement (anything that is run in Raku is), however, what it's not is an expression. do is a statement prefix, and what it does is turn statements into expressions.
However, if is not really a first-class function that you can assign to a variable or handle around. Whenever you find pieces of syntax such as that one (or for, for instance), you need to prefix them with do to "expressionify" them.
say &say.^name;# OUTPUT: «Sub» say &do.^name; # OUTPUT: «===SORRY!=== Error while compiling <tmp>Undeclared routine:...
say &if.^name; # OUTPUT: «===SORRY!=== Error while compiling <tmp>Undeclared routine: if used at line 1»
So if, by itself, does not create a block, it does not create an expression, it simply creates a statement. You need to precede it with do if you want it to actually turn it into a expression. It does run the block that's behind it, however.
Let's go back to the original question, statements and blocks. Blocks are objects, first-class citizens. You can use them, apply them, pass them around.
my &ifs = { if $_ {34} else {43}};
ifs(True).say; # OUTPUT: «34»
Statements are throwaway blocks you simply run. In some cases, they are also expressions: they yield a result which, then, you can assign.
my &ifs = { if $_ {34} else {43}};
my $result = ifs(True).say; # OUTPUT: «34»
say $result; # OUTPUT: «True»
The ifs(True).say statement prints to output, it also produces a result that can be assigned. All three lines are also statements, and as a matter of fact, expressions too.
Some control structures, however, do not create expressions.
Some others do; for creates a expression; while does not.
if is an example of this. They don't produce a result. You use them for the side effects: running a statement (if true) or another (if not). You might turn them into a block, as above, and pass them around. Or you can just precede them with do and make them produce a throwaway result, which you can then use.
So it will very much depend on your actual use case. You can surround the if statement with curly braces and create a block; or you can simply use the result creating an expression. Or you might want to use it just for the side effects, doing nothing.
I am trying to use an if statement with a variable in my expression and I get no results. The variable works when I use the variable on it's own but when used with the if I get no results.
I have tried:
if(OrderQtr='Apr-Jun 2018',$(vAvgOrderCost),0)
if(OrderQtr='Apr-Jun 2018',sum($(vAvgOrderCost)),0)
sum($(vAvgOrderCost)if(OrderQtr='Apr-Jun 2018',0))
Nothing seems to work. Thanks
Variables in QlikView are used as a text replace feature, so be carefull. If your variable hold a value like 1,345 an expression like "if(OrderQtr='Apr-Jun 2018',$(vAvgOrderCost),0)" will be translated into "if(OrderQtr='Apr-Jun 2018',1,345,0)" which by itself will be a syntax error.
Something like :
Num(if(OrderQtr='Apr-Jun 2018','$(vAvgOrderCost)','0'))
would be a safe way to go.
the if() syntax should work like this if(test,true,false)
So looking at your examples I suspect this is what you are trying to do
sum(if(OrderQtr='Apr-Jun 2018',$(vAvgOrderCost),0))
Workfusion I am trying to make two variables through web-element. When running individually its great but when running separately it has problems.
Please see the picture for the same. This doesn't get executed.
If your XPath has any variable then try the giving a value like following:
//*[#id="mv-tiles"]/a[${i}]
and you can keep changing value of i through loop. A variable inside another will throw error in Workfusion RPA Express.
The ${} evaluates the whole it's body.
Does the following, without nested ${} execute OK?
${webrange[countertemp]}
Is there any reason that this syntax shouldn't work in Qlikview load script??
Let v_myNumber = year(today());
Let v_myString = '2017-08';
If left($(v_myString),4) = text($(v_myNumber)) Then
'do something
Else
'do something else
End If;
I've tried both ways where I convert variable string to number and evaluate against the number variable directly and this way. They won't evaluate to equivalence when they should..
Left function is expecting a string as is getting something else as a parameter. As you are currently doing, the function will be called as Left(2017-08, 4) which is unhandle by QlikView.
If you use Left('$(v_myString)',4), it will evaluate as Left('2017-08', 4) as work as expected. Just adding quotes around the variable it should work.
Although QlikView calls them variables, they should really be seen as "stuff to replaced (at sometimes evaluated) at runtime", which is slightly different from a standard "variable" behaviour.
Dollar sign expansion is a big subject, but in short:
if you are setting a variable - no need for $().
if you are using a variable - you can use $(). depends on its context.
if you are using a variable that needs to be evaluated - you have to use $().
for example in a load script: let var1 = 'if(a=1,1,2)' - here later on the script you will probably want to use this variable as $(var1) so it will be evaluated on the fly...
I hope its a little more clear now. variable can be used in many ways at even can take parameters!
for example:
var2 = $1*$2
and then you can use like this: $(var2(2,3)) which will yield 6
For further exploration of this, I would suggest reading this
Why does this fail:
<CFIF isdefined("URL.3dfile")>...</CFIF>
with following message:
Parameter 1 of function IsDefined, which is now URL.3dfile, must be a syntactically valid variable name.
and this won't:
<CFIF structkeyexists(URL,"3dfile")>...</CFIF>
Is the way it get's parsed not much the same? And .. are variables starting with numbers invalid or aren't they?
Seybsen - variables names should not begin with a number. This is likely a legacy of older non-java version of CF Where a variable was not part of an object.
However, in the java world everything IS an object. This leads to a syntactical nuance. If you are using variable names in dotted notation your var name will likely throw an error. But use it in other ways and it will succeed.
So this sort of syntax works
url['33foo']
But setting a variable name directly - 33foo = true - will not work.
Here's a post with a full explanation.
http://www.coldfusionmuse.com/index.cfm/2005/9/8/isdefined%20vs%20structkeyexists