Passing a variable to a command in a script

Question

I've been searching all over the place and since I'm taking my first steps in PERL this might be one of he dumbest questions but here it goes.

So I'm creating a script to manage my windows and later bind it to keyboard shortcuts, so I I'm trying to run a command and passing some variables:

my $command = `wmctrl -r :ACTIVE: -e 0,0,0,$monitors->{1}->{'width'}/2,$monitors->{1}->{'height'}`;

But I get an error saying I'm not passing the right parameters to the command, but if I do this, everything works great:

my $test = $monitors->{1}->{'width'}/2;
my $command = `wmctrl -r :ACTIVE: -e 0,0,0,$test,$monitors->{1}->{'height'}`;

So do I really have to do this? assign it first to a variable and then pass it, or there's a more elegant way of doing it?

clt60 · Accepted Answer · 2014-07-25 00:21:59Z

3

The backticks operator (or the qx{}) accepts A string which is (possibly) interpolated. So accepts string and not expression like $var/2.

Thats mean than the $variables ($var->{1}->{some} too) are expanded but not the arithmetic expressions.

Therefore your 2 step variant works, but not the first.

If you want evaluate an expression inside the string you can use the next:

my $ans=42;
print "The @{[ $ans/2 ]} is only the half of answer\n";

prints

The 21 is only the half of answer

but it is not very readable, so better and elegant is what you're already doing - calculate the command argument in andvace, and to the qx{} or backticks only pass the calculated $variables.

answered Jul 25, 2014 at 0:21

clt60

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