so the posted code works?

my $last, $now)= '0';
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What is this supposed to do? Initialize both $last and $now to '0'? Guess again...

my $last = my $now = '0';
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works better ;-)

btw, what is this supposed to do:

system(`$1`);
return $now;
print "I done $1";
last
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The last two lines will never get executed... never! BTW: why do you use backticks in your system() sub? It's either `$1`, or do{ open(my $cmdh, '-|', $1); <$cmdh> } or system($1)... but combining two of them is probably not what you want to do...
and... you might wanna write those 4 lines in a different order:

`$1`;
print qq{I've done $1};
return $now
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3 lines... does the same thing ;)

cya!